Question about collimated display systems. [Archive]

castle

10-15-2010, 08:22 AM

I'm kind of the same mind set regards a DIY collimated display. BTW the link to the short video was cool.

Part of the problem is in the precision required to shape and hold the Mylar in position, then you need to construct the curved screen on which to back project the image(s), then a projector lens to keep things in focus by accounting for the changes in the throw distance projecting a flat image onto the back of the curved screen. You might be able to use a front projection system -- easier to build a solid opaque curved surface but still need to find an appropriate lens system.

Engineering and building the curved mylar mirror is the greatest challenge. Looking at the video portion showing the mirror was informative as to the shape but very little on the vacuum system. Need to come up with some numbers to describe the mirror's geometry. Also speculating the mylar as to quite flexible to stretch in two directions so as to create a snug fit against the spherical surface. Try wrapping some mylar or any sheet of material around a sphere and you get the idea.

As shown in the video the size of the visual system also requires a little more expertise than simply throwing up a 4x8' white board

Maybe a good project to tackle in 2011....

JW

Mike.Powell

10-15-2010, 10:22 AM

Most cross-cockpit collimated displays are rear projected. Here's a link to a marketing video showing the general layout: http://www.q4services.com/images/supravue001.mov The company hosting the video, Q4 Services, provides maintenance for Mylar mirrors for just about all types of simulators.

RSI Visuals is a small company that offers a front projected collimated display. The projection path uses a spherical-section fold mirror just above the collimation mirror. http://www.redifun.com/r/products.php?product=3&category=14 Front projection has the disadvantage of requiring a second mirror, but can offer higher contrast and brighter images for the same projector light output. Rear projection has significant issues with back surface reflections.

mikesblack

10-15-2010, 07:04 PM

Thanks you castle and thank you Mike. Mike I appreciate the links, especially the "Supraview" movie.

I have perhaps way too many questions. I wonder if either of you or others can address the following.

If one were to start such a project, would it make most sense to first construct the visual mirror with the idea that the other components, be they front or rear projection screen projector/ first mirror, etc, being easier to make the neccessary adjustments . I assume there would be no final adjustments that could be put in place to vary the viewing mirror. So the mirror would have to be done correctly.

I have yet to experiment with N Thusim/ Sol 7, but I can only imagine an image from a parabolic mirror that is not buit with accuracy and neccesary precision could not be compensated with the pre warp process of the 2 d image this software provides.

So then the mirror.
First: Size: I can only afford a 6.5 foot radius. So would the first image need to be created on a 3.25 foot radius spherical screen? Is this even possible with Sol 7?

If this size is not a problem, what must the proper geomety for viwing mirror? I imagine a perfect sherical shape would be constant radius horizontally and vertically? I would want 220 degree viewing and I haven't considered the vertical amount yet.

Orientation of mirror to preimage. It seems there must be some way to prevent the mirror from capturing the simulator shell or any other non image related visual artifact. The examples I have seen so far are of a mirror designed to curve up and out, like a bowl. This way the orrientation is up away from the shell and only on the first projection surface.

Consistancy of mirror surface. Obviously no rinkles. This then is the role of the vacume pump. So some questions about this. Are there any other materials with good mirror surfaces that could be glued on, even painted or moulded so that the vacume pump part could be avoided? Not sure how this was done, but this is an interesting image I found. http://www.dailymail.co.uk/sciencetech/article-1177103/Turning-life-upside-Artist-creates-fantastical-landscape-giant-concave-mirror.html
If not, how would one need to prepare the mylar sheet. Before applying to a vacume box shaped accourdingly. How would the the mylar be cut to accomidate the shape? would it be glued down? Taped? Tacked?

Thanks so much.

Mike.Powell

10-15-2010, 09:00 PM

I've been seriously researching collimated displays for inclusion in an upcoming book on simulator/computer-gaming display systems; however, I don't have all the answers yet. (I sporadically post progress reports on my website.) Here are some thoughts:

The best source of information is searching patents though Google. Patents include a section on prior art to illustrate the shortcoming the new invention is supposed to overcome. Then, of course, the patents describe the new ideas. The writing all seems to be twisted 19th century legalese. Fortunately, there are a lot of pictures. Good search terms are "infinity display", "film mirror", and "collimated display". Check out patents #3,432,219, #3,659,920, #3,785,715, #5,253,116 for starters. There are lots more.

The collimating mirror is a spherical-section of radius R. For proper focus and collimation the image must be located near or on the mirror focal surface which is a spherical-section surface of radius R/2. The mirror focal surface has the same center of curvature as the mirror. The pictures in the sales literature looks otherwise, but they really do have the same center. The odd look is because cross-cockpit collimated displays use off-axis optical paths.

R can be small or huge. Collimated systems have been built for head mounted displays and for wide-body aircraft simulators. You can scale it to meet your needs.

The field of view details can be worked out with ray tracing and high school trig and geometry. Ray tracing with a CAD drawing system works well. I've been using TurboCAD. DoubleCAD XT would probably work and it's free.

Metalized Mylar can be used to make film collimating mirrors. Up to about 40 degrees of vertical field of view, building one is merely difficult. Building one with a 60 degree vertical field of view apparently requires magic. SEOS figured it out a few years ago. Rockwell Collins was so impressed they acquired SEOS in 2008.

I agree. Start with the mirror. If the mirror doesn't work out, nothing else matters.

castle

10-16-2010, 12:31 AM

Some other technique other than a vacuum system to hold the mylar will not work. I tired glue with very poor results.

Built a small frame, 5' radius, 60hx45v degrees FOV, just no way to get a smooth application of glue and no matter how thin I spread the glue, the mylar always had bumps and irregularities, and it was impossible to "stretch" the mylar to make it conform to the surface.

So you need to devise a manufacturing process to precisely create a concave surface that is very smooth and uniform. I imagine you could tolerate some variation in precision but it would not be much. And don't forget the projection screen has to be quite precise as well.

Another problem to solve would be some non-uniformity of the mylar attach points along the edges which will result in variations in the tension applied to the mylar. This would be a problem if the mylar was "free standing" and relying on the vacuum to control the shape. If you suck the mylar onto a solid surface, imagine that should not be a problem.

I don't have the links handy but the technique of deforming mylar and glass mirrors with a vacuum has been used by astronomers to produce optical collection mirrors starting in the '80s. The mirrors were much smaller and they actually used the vacuum as a control function to achieve dynamic focusing of the mirror.

My approach would be to pick some arbitrary size as noted above, maybe even smaller, and focus on the mechanical and manufacturing details. That is one question I'm still puzzling over --- does the vacuum actually shape the mylar attached to a frame or simply suck it onto a surface that defines the shape?

One other consideration I've not researched yet is the lens requirements and what f-stop is required to project the image onto a curved screen that is "nearly" in focus everywhere or some other lens arrangement to handle the problem.

JW

mikesblack

10-16-2010, 03:36 PM

I just bought a roll, so can't wait to experiment.

My thoughts are to use phenolic or other soft flex material cut into long narrow strips that would act to clamp down on the Mylar film. The strips would be set front and back along the edge of the Mylar sheet. I would need to figure out the interval for spacing drill holes. The idea is to not only hold the Mylar in place, but also to prevent wrinkling at the edges, so there would need to be a tight enough, but also fairly uniform holding pressure all along.

These strips would fit into a track that would be set in the semi sphere frame along the mirrors border. I imagine this track would be made of the same material. The track would need to be snug, but also air tight for suction. I imagine perhaps using a router so that a grove can accommodate the phenolic track housing . The track groove would need to be set square and consistent along a precise arc.

The material should slide into place. I would also need to have these strips set along the vertical edge. Perhaps the track groove would be set so that the track would lie into the frame, set back down.

I need to figure out how much play there is in the Mylar and how and how cut and bunch the material prior to affixing the track. From the movie link that I provided, seems the Mylar prior to suction shows wrinkles at 45 degrees to vertical. Sort of reminds me of those old instant popcorn tin tops that were twisted or rotated so that when the tin expanded with the popping it would expand and rotate out. This is an exaggeration as the wrinkles on the mirror are very slight, but perhaps telling none the less.

Lots of unknowns, so I too will start with smaller models, e.g. 1-2 foot radius. Perhaps in time we'll get it figured out. I know that it would be a terrific enhancement. We shall see what challenges lie ahead. I'll keep you all posted as I progress, or not.

geneb

10-16-2010, 10:42 PM

castle

10-16-2010, 11:51 PM

That is one fine pic of one fine piece of work and craftmanship. Yes, drawing the mylar against a solid surface is the way to go. Would be most interested on how you construct the surface and the tolerances you are working with. I guessing that is plywood or some other type of non permeable material.

Hers is a suggestion on "attaching" the mylar.

Rather than trying to pre-measure the material and attaching it, first construct your frame and surface and the vacuum system. get some sort of "referee" material, cut it into sections, turn on the vacuum, and slap the strips in place. Cut an oversized piece of mylar that you know will extend beyond the edges of the frame. Roughly position the mylar against the "referee" material. Once the mylar is sort of in position, remove a section of the "referee" material by sliding it out from under the mylar. Hopefully, the mylar will be drawn against the surface. Continue until all the strips are removed.

If that works and the mylar is in position, simply mark the attach points on the mylar or maintain the vacuum and secure the mylar to the frame, shut down the vacuum and trim as required.

Warning, I've NOT tried this myself. Just a crazy idea.

JW

mikesblack

10-17-2010, 12:28 AM

mikesblack

10-17-2010, 12:36 AM

Thanks castle

Can you explain "referee material"? Not quite sure I understand exactly what you have in mind.

Thanks.

geneb

10-17-2010, 01:12 AM

Great work! Curious about R. I was considering 6 feet and 30 degrees vertical but if there isn,t a disadvantage going to 5 or less feet, it would make for moe space in an already crammed room. Do you have any ideas on this?

Mikesblack, you realize a 6 foot radius will give you an edge-to-edge width of 12 feet, right? The radius of the screen is going to be dictated by the size of the simulator cab. I picked 48" because I can use it with a couple of different cockpits - IF it works. Making even a "good enough" thin film mirror is a brass plated nightmare. :)

BTW - wledzian, I've got the projectors set up and running, so if you want to stop by and see it in action, let me know. I'm going to be taking it down at some point in order to move it, so let me know as soon as you can. :)

Here's what my next step looks like:
http://www.diy-cockpits.org/coll/images/frame_insert.jpg

The gray colored components need to be cut out, but with any luck I'll be able to do that tomorrow.

g.

castle

10-17-2010, 02:12 AM

Referee material --- anything that would block the holes and create a suction and substitute for the mylar. wrapping paper, aluminum foil, 8x11 paper sheets, etc.

Would also be a way to test your vacuum system and seals by blocking air flow through the pin holes and use smoke to see if air is being sucked in from other spots on the frame or joints.

JW

geneb

10-17-2010, 11:20 AM

"Reference" material maybe? :)

g.

mikesblack

10-17-2010, 12:13 PM

Thanks for explaining. I understand what you mean. Makes good sense.

On a separate note, I would love to find some plans or blueprints of these level D C. display systems. That would take out much of the guesswork.

I wonder how helpful the manufacturers would be if someone called over to explain that he or she was a hobbyist, looking for some helpful ideas or information. I wonder if the response would be guarded. Perhaps a manufacturer would be resistant to help someone if they thought by sharing could compromise their competitive advantage.

I have found Mike P. work and links to be a great help, so thank you Mike. I look forward to your new book. I have been reading your second book of late. Very interesting indeed. I'm sure I'll continue to check out your site for updates on this.

I will be happy to share what I find as I gather more information and look forward to exchanging ideas on this. Given that this seems like uncharted waters for the general DIY guy or gal, makes it even more intriguing.

mikesblack

10-17-2010, 12:48 PM

geneb,
My pit is 11.5 ft across at the floor and at the back. I have roughly 2 ft from side of pit to my wall, perhaps a little less on the other side. I am considering that my radius origin is located at the throttles in the center of the cockpit. The widest part of the circle and where I am measuring R is at the top of the Mylar screen, where the angle relative to the floor is 90 degrees.

I'm considering the following.

Angle of arc from bottom to top of screen. Whatever I can do in order to keep the Mylar material wrinkle free. Width based on the arc based on 30 degrees and r= 6 feet is approx. 3 feet assuming my math is correct. ( 2Pi R) = approx. 36 ft diameter. So At 10 degrees of arc( 36/36) = 1 foot. I need to be sure that when I look out of the cockpit window I have enough viewing surface above and below cockpit window so there isn't an interruption to the image. If I bring these elements into consideration perhaps I might get away with 3 feet viewing surface. I need to experiment with curves of various radii and arc to see what will work.

castle

10-17-2010, 01:02 PM

Matt Olieman

10-17-2010, 01:37 PM

Just in case you've not found this site and want more info on concave mirrors and optics..

http://www.physicsclassroom.com/class/refln/u13l3d.cfm

Your instincts are probably correct, no manufacturer is going to supply details, trade secrets, and proprietary data to a voice on the phone no matter how sincere, honest, and trustworthy the caller may be. Afraid we're on our own here. OTOH there are some very bright, intelligent, and creative folks in the hobby side of simming as well as those on these forums.

Plus we're not going for FAA Level D certification. Close enough works for me ;-)

Good link JW. There lies the problem, the technological, know how and the resources for R&D. We can have all the information regarding how it's done, but when it comes down to the bottom line....... it's nearly impossible for one person to take on this task and I'm just talking about the mylar mirror. The overhead rear projection screen is in itself a major or almost impossible undertaking, if you really think about it. Between the two of them, there is no room for imperfection.

I've researched this for over 15 years, I've tried all sorts of mirror setups, I've studied actual mirrors on a level D sim. I've got rolls of Mylar, different thicknesses and qualities. Even to stretch mylar on a flat surface is a feat itself. Try to find an imperfect piece of mylar.... wow, the frustrations.

If some one can find a way of making this happen, this person will be THE hero of our hobby. :)

Matt Olieman

Mike.Powell

10-17-2010, 03:39 PM

There were a series of reports funded by government money all with the appealing title, "Wide Angle Multiviewer Infinity Display Design". So far I've run across abstracts for 3 different reports with this name. They appear to be have been distributed in micro fiche format to a few university libraries. None of the libraries will send micro fiche out as an inter-library loan. It is possible to buy hard copies from the NTIS for $48 to $60 each. Not being able to preview them, I'm reluctant to spend the money, especially because there is no guarantee that the print-on-demand from old micro fiche will be of readable quality. There is also the issue of just exactly what the reports contain. The abstracts sound appealing, but there is no indication of the level of detail or its usefulness.

I've considered driving to UC Davis California to visit the library as the catalog says they have two of the reports, but I haven't gotten there yet.

If any of you gentlemen are located near a good university engineering library, you might check to see if these reports are available there. They might be full of gold plated hand waving, or they might be real gold mines for this project.

castle

10-17-2010, 04:20 PM

Hi Mike,

Were Rhinehart and Shaffer some of the authors of these reports? Any more info such as fiche numbers.

JW

Mike.Powell

10-17-2010, 05:06 PM

Hi Mike,

Were Rhinehart and Shaffer some of the authors of these reports? Any more info such as fiche numbers.

JW

Here's what I've got so far:

Wide-Angle, Multiviewer Infinity Display Design by L.W. Shaffer, J.A. Waldelich; Air Force Human Resources Laboratory, Advanced Systems Division, [1977] NTIS product code# ADA053679, Library call: DOC D 301.45/27:77-67 mf11 [@ UCDavis Shields Library]

Wide-Angle, Multiviewer Infinity Display Design by Robert M Rhinehart; Air Force Human Resources Laboratory, Advanced Systems Division, [1977] NTIS product code# ADA051158, Library call: DOC D 301.45/27:77-71 mf11 [@ UCDavis Shields Library]

Wide-Angle, Multiviewer Infinity Display Design by Ian Whyte, A.W. Zepf; Brooks Sir Force Base, TX. : Air Force Human Resources Laboratory, Air Force System Command, [1982] NTIS product code# ADA116308 , Library call: D301.45/27:81-27/V.1-2 [@ New Mexico State Library] Series: AFHRL-TR ; 81-27 (I-II)

NTIS is the US Department of Commerce National Technical Information Service www.ntis.gov

Doing a Google search on the title turns up various links, but no real content. There's even an entry in Google book scan, but no preview.

Mike.Powell

10-17-2010, 05:48 PM

I found these abstracts listed in the bibliography of the AF Human Resources Lab. http://www.icodap.org/papers/AFHRL/index.html

Whyte, I., & Zepf, A.W. Wide-angle, multiviewer , infinity display system. AFHRL-TR-81-27(I), ADA116 308. Williams AFB, AZ: Operations Training Division, June 1982. Project ILIR, Contract F3361S-79-C-0002, American Airlines. NTIS. This study examined the design specification for a wide angle infinity display system with minimal distortion, convergence, dipvergence, and collimation errors for use on wide-body-aircraft simulators. The report includes a recommended final design specification; a survey of potential fabrication technologies for projector, screen and large mirrors; an approach to fabrication of a large display system; and finally, assembly and alignment techniques of mirror segments for a large display. (Note: Dipvergence refers to vertical movement of eyes up and down as opposed to side to side. (94 pages)

Shaffer, L.W ., & Waidelich, J.A. Wide-angle, multiviewer infinity display design . AFHRL,-TR-77-67, AD-A051 158 . Wright-[Patterson AFB, OH : Advanced Systems Division, September 1977 .Project 6114, Contract F33615-76-C-0064, General Electric Company. NTIS. There has long been aneed in aircraft simulation for a wide angle visual display that will accommodate the entire crew of a large aircraft type such as a bomber or tanker. This study is concerned with the approach and design of a wide angle display for multiple crew members in large aircraft simulators . The study traces the development of a concept from existing simulation methods. Throughout its 180° by GO° field of view which accommodates pilot, copilot, and instructor pilot the final design meets most of the requirements of the original specification . Because of its relatively large optical components the fabrication of the display will be of a developmental nature itself . (116 pp.)

Rhinehart, R.M. Wide-angle, maaltiviewer infinity display design . AFHRL-TR-77-71, AD-A053 679. Wright-Patterson AFB, OH: Advanced Systems Division, December 1977 . Project 6114, Contract F33615-76-G0052, McDonnell Douglas Electronics Company. NTIS. A research design study was undertaken to define an extended field of view (60° x 180°) infinity image display, suitable for multiviewer use on wide-bodied aircraft simulators. Mosaicking of single channel units, both reflective and refractive was investigated, along with extended field, off'-axis reflective systems. Major emphasis was placed on the investigation of extended field of view, off-axis reflective systems. Various figured screen and mirror combinations, ranging from spherical to high order aspherics, were designed and evaluated. Two specific designs were selected, optimized and evaluated over an extended viewing volume. (78 pp.)

Mike.Powell

10-17-2010, 07:27 PM

I found the Whyte & Zepf report for sale in pdf from NTIS. I bought and downloaded it. It is interesting in, shall we say, a historical way. It does not mention film mirrors at all. The optical design reflects very early approaches to the cross-cockpit design goal.

My thought is that information in recent patents is both more detailed and more useful.

castle

10-17-2010, 08:06 PM

Thanks, Mike

I would put my money on the 1982 study. If the abstract is accurate, the phrase "approach to fabrication" might provide some insight. While they all are a bit dated. might still be a good starting point.

You can download an electronic copy of the 1982 Project ILIR study for $15 from NTIS. Catch is that file is reproduced from "best digital master available", that could mean an optical scan of an old micro-fiche. Think I'll give then call tomorrow....

JW

castle

10-17-2010, 08:09 PM

He, he, guess I won't call them.

mikesblack

10-17-2010, 08:15 PM

Mike,

Thank you very much for all of this as well as your insights.

mikesblack

10-17-2010, 08:38 PM

Matt,
Can you say from your experiences what the most demanding element you found was? Sounds like there are a bunch, but at any point did you think there was possibility you might have been close to getting it.
It sounds like you have encountered too many obstacles to feel satisfied continuing or that it may be a further exercise in futility to care to bother with it all. After all, this is supposed to be fun.
That said, I should think that your many years of exhaustive and frustrating experience trying to build this has led to many valuable insights that could be of tremendous value. I wonder if you think that a collaborative undertaking by this community and most especially with your rich experiences could be what it takes to make this at all plausible.
At the end of the day, the technology is there and it is a physically reality practically speaking. I would be most grateful for your insight and experience, so long as you come to find it worth your time to do so. With that and the input of diversity of this interested crowd, who knows, perhaps we'll get there.
Thanks,
Mike

Matt Olieman

10-17-2010, 09:20 PM

Mike (mikesblack), the first question that comes to mind, are we capable to form a cast for the mylar mirror? The answer is yes. Secondly can we vacuum form the mylar to the cast? The answer again is yes. So than where lies the problem, it's the imperfections in the mirror or the mold. First the mold has to be perfectly curved to act as lens and align with the curvature of the rear projection screen. Secondly foremost difficult part is the imperfections in the curve, a slightly flattened portion of the mold (mirror) and the whole mirror is out of whack.

Obviously, the mold can not be hand made, there is a tremendous amount of precision involved to make this work, that's the major short fall of a self made collimating mirror.

There is a video floating somewhere, at I saw within the past several years, where they showed to vacuum fit of the mylar to the form (mold). I was surprised how quickly it took place. The tiny holes in the mold has to be 10's of thousands and very small as not to have the slightest imperfection. The mylar is actually glued to the mold.

The development cost of a collimating mirror would be tremendous compared to buying a ready made mirror and screen. Then comes the high resolution projectors and then the special lenses, where talking about thousands of dollars for a single lens.

Mike Powell has presented amazing technical information regarding design of the collimating mirror for a cockpit, it certainly gives you a jump start. Even if you had the exact specifications, the above mentioned obstacles would still be there.

I'm not saying it can't be done, it's a matter of how much money you want to spend. I hope someone does come up with a solution to make an affordable design for a cockpit collimating mirror.

I hope I made some sense out of what I wrote, sometimes a just babble...... :) :) :)

Matt Olieman

mikesblack

10-17-2010, 10:35 PM

Matt,

Not at all. I appreciate your reply and If you don't mind, I have a few questions for you.

You mentioned many things. I'd love to find this video and if you know or find a link, I would be most grateful.

You mentioned here and I believe in another post on this topic that the Mylar is glued to the mold. Are you saying that the suction acts as a one-time process for which it enables the Mylar to be spread uniformly and finally joined permanently by glue? I was thinking that the vacuum was actually part of the set up that was used to keep the Mylar held to the mold and used continuously.

Also, do you have any idea what sort of result one would find using conventional projectors, assuming a good mirror, projection screen set up?

I have no idea the scope and scale of this project, so forgive my naiveté or simplistic thinking. If nothing else, I am always happy to learn new things.

Mike

Neil Hewitt

10-17-2010, 11:36 PM

If you wanted to go for a simpler solution, it might be within a hobbyist's power to create a WAC (Wide-Angle Collimated) window display unit. Older sims used them, before large mirrors were practical, and plenty of sims still have them in today. You can still buy them new, too. Basically they use the same parabolic mirror as the cross-cockpit display but the mirror is sized for the window it's put in front of - the radius of the mirror being just a little larger than the width of the window. Put a half-silvered mirror directly in front of you at 45 degrees, then up top, put a CRT (I suppose you could use a very bright TFT) looking directly down onto the half-silvered mirror. The picture on the monitor is reflected onto the spherical mirror and then back at you, duly collimated. Get the focal length right, position the mirror and yourself in the right place, and bingo.

There are surprisingly few actual pictures of this in the internet, which is annoying... Matt Ford has a good section on his site about his Level D display system salvaged from an old Boeing sim which uses WACs:

http://web.me.com/mattford1/Site/Level_D_Visual_System.html

The key is the mirror. You can get concave spherical acrylic mirrors from science and educational supply outfits, these are sometimes used by people creating solar stoves. I found one with a diameter of 600mm - can't find the link now, unfortunately - and it's possible they may go bigger. At 800mm - 1000mm they'd become useful for front-view windows on a smaller cockpit. Many are not a single mirror surface but made from strips of reflective material with joins, which is OK for a solar stove but not for sim use.

For a fighter pit or any kind of pit with small windows - maybe a GA pit? - this might be a goer. I doubt you'd be able to buy mirrors big enough for a heavy jet simpit without going to custom fabrication. You'd also have a lot of unneeded top and bottom to the mirror which you couldn't just cut off because the mirror would then deform. Probably have to cover the unused bits in black.

It's interesting that it seems very easy to get hold of reasonably large convex spherical mirrors - lots of companies sell big ones you put up in a corner of a warehouse so you can see all around you - but concave mirrors, not so much. Plus of course not just any old concave mirror will do.

I suppose at smaller sizes - up to a meter in diameter - you might get your local friendly plastics company to make you a few as a job lot.

But I think the full-on precision machined mirror you need for a cross-cockpit display is just beyond the capabilities of anyone without a proper manufacturing plant at his or her disposal. I suppose Matt Sheils might be able to manage it :)

castle

10-18-2010, 01:55 AM

I went back to take another look at the "how it's made" video. Somethings to note.

The shape of the mirror section seems to indicate that the top edge starts at a latitude below the equator and and looks to be much closer to the "south pole" wherein the lower circumfernece or line of latitude has a much smaller radius than the upper latitude. Eyeballing it might be something like lat 20 degrees south to say around 50 degrees south.

The vertical curve along the top edge appears to have a rather large radius and is greater than the lower radius. If the person in the scene is 6 feet tall, my guess is that the radius of the sphere from which the mirror section is mapped is close to 15feet or more. Keep in mind the radius of the Artic Circle is much less than the radius of the Equator. Tough to tell as there is probably some distortion with the camera and depth of the image due to the lens. Note how the yellow beams of the holding frame are curved. I'll bet lunch that those beams are, in fact, straight.

The other item to note is the closeness of the projection screen to the mirror as it is visible when the scene shows the mirror moving into position.. Clearly, the projection screen is inside the focus of the mirror which produces the larger virtual image for the OTW. Also the view from inside the cockpit shows the mirror with wrinkles, so that would argue for an active vacuum system. Or did Matt really mean to say "glue" as in the sticky stuff.

Mike, you might want to rethink your calculations as to size, location, and perspective. The projection screen clearly overhangs the cockpit shell and can only be a few feet from the mirror.

Matt is right, It is a tough problem but I always like a challenge :-)

JW

Matt Olieman

10-18-2010, 08:13 AM

Concave spherical mirror. Thanks Neilh, I couldn't think of that term. :)

JW I'm with you, it's a tough problem and a fantastic challenge...... anybody..... GO FOR IT!!!! :)

Mike (mikesblack), The video..... :) I'll do my best to find it. Regarding the Mylar being glued. The vacuum holds it in place for several hours as the glue cures (yes, the sticky stuff :) ). They did not mention what the glue was, but I amagine something that would not cause imperfections.

Regarding the individual Concave spherical mirror, yes, Matt Ford uses it on his cockpit, you can find pics of it in the "March 2010" Builder of the month. Go HERE. (http://www.mycockpit.org/forums/content.php/143-Builder-of-Month-March-2010) Project Magenta's Flight sims use the individual concave spherical mirrors, matter of fact at one time they were selling them for around $4K each (NEW). I considered it. If you ever flew a sim with these type of mirrors it would not take long to be a bit frustrated, particularly if you want to be wrapped with scenery. If you're in the CPT seat, you can't see out of the F/O window, all though you can see out of the side windows. If you were able to see the F/O window, you would see the identical image as the CPT side (they are the same).

There is a GA Sim, I think a C172 that uses the individual Concave spherical mirror. I believe there are some posts here and pics of the sims progress, it was a school project in Europe (I think).

Regarding how close the mirror is to the overhead screen. The first time I walked between the cockpit and the mirror, I was amazed how close they were. First of all, from inside the cockpit, it gives you the impression the mirror has quite a bit of distance.... what an illusion!!! :) I was constantly reminded.... "DON'T TOUCH THE MIRROR!!!!" :)

This is an amazing topic and a fantastic challenge, I know...... I believe in our hobby we've conquered every aspect of building a Flight Sim Cockpit, except the concave spherical mirror, 150 to 180 degrees.

There was a time where builders believed, motion for the sim was not practical to make and was way beyond our budget. Someone in New Zeeland came up with an idea using Automobile axels, starter motors and other parts and made a full motion sim for around $3,000. We've developed further than that, and all sorts of contraptions are available in affordable form.

Our hobby still is not a cheap hobby, but compared to 8 to 9 years ago, you can build a sim for much less, AND it's plug and play. :) :) :) Oh well..... I can go on and on.... LOL.

I see hope for the 150 to 180 degree collimating mirror for the home build cockpit....

Matt Olieman

geneb

10-18-2010, 09:10 AM

geneb,
My pit is 11.5 ft across at the floor and at the back. I have roughly 2 ft from side of pit to my wall, perhaps a little less on the other side. I am considering that my radius origin is located at the throttles in the center of the cockpit. The widest part of the circle and where I am measuring R is at the top of the Mylar screen, where the angle relative to the floor is 90 degrees.

That makes sense. I just wanted to make sure you were aware of the size requirements. :D

I'm considering the following.

Angle of arc from bottom to top of screen. Whatever I can do in order to keep the Mylar material wrinkle free. Width based on the arc based on 30 degrees and r= 6 feet is approx. 3 feet assuming my math is correct. ( 2Pi R) = approx. 36 ft diameter. So At 10 degrees of arc( 36/36) = 1 foot. I need to be sure that when I look out of the cockpit window I have enough viewing surface above and below cockpit window so there isn't an interruption to the image. If I bring these elements into consideration perhaps I might get away with 3 feet viewing surface. I need to experiment with curves of various radii and arc to see what will work.

Keep the mirror as close to the cab as you can without it shadowing the image and you'll be fine. There will be some experimenting for sure though. :)

g.

castle

10-18-2010, 11:58 AM

Mike,

I came up with slightly higher numbers..

If you want a mirror that subtends 45 degrees of arc which seems to be the standard size, ( don't think 30 degrees will provide a sufficient FOV) for mirror with 6' radius

(45.0/57.2957) * 6.0 = 4.712 feet

you might be able to get by with a 5' radius mirror in which case you will need

(45.0/57.2957) * 5.0 = 3.92 feet

Neil Hewitt

10-18-2010, 01:58 PM

I wonder what the effect would be if you took an acrylic mirror sheet and bent it into a parabolic curve just in one direction - horizontally - and then put a similarly-curved and appropriately scaled rear-projection screen at the focal point and projected onto that screen? Would you get partial collimation? What would that look like? I don't know enough optics to really think it through. I'm sure the reflected image would be distorted vertically at the corners, but if you removed that distortion using NTHUSIM what would the end result look like? Would your eye see it at a near focus or infinity or some kind of half-way house? Precisely bending acrylic mirror sheet into a simple curve is well within the capabilities of many people here.

Also - acrylic mirror sheet is basically clear acrylic with mylar on top / underneath. If the curve was gentle enough - say, using a large parabolic satellite dish, if you could get hold of one, as a mould - and you heated the acrylic up enough to be formable, would the mylar cope with the scretching and deforming without cracking or seaming? Could you even get the mylar film up to that temperature without it burning off? Anyone tried that?

I suppose you could maybe make several sectional moulds of an overall mirror shape using heavy-duty polystyrene blocks which are easy to carve and adjust, form acrylic to each one using the heat-it-in-the-oven technique, then look at mylar-covering each segment individually. That'd surely be easier to do? Yes, you'd get a less perfect display, but it'd be better than nothing by a long way.

Just throwing out ideas here...

mikesblack

10-18-2010, 02:55 PM

I like those ideas neilh. I too wonder about the horizontal curve only. At least in terms of simulating paralax and proper runway allignment per Cpt or FO seat. This is something I will experiment with when I start to work with the mylar.

ANDYSMITH

10-18-2010, 06:08 PM

Hi all,
I like the idea of the one dimentional curved mirror(cheap) and the problem I see is that it can not be mounted vertical, as in 90 degrees to your eyes. Because the "screen" must be over your head, you need to tip the mirror back at an angle to see the screen that is above and behind you. This will give your horizon a curve that can be at the right elevation directly ahead but will turn up at the outer edges like a smilley face. So my question for the day is would this "Immersive Display Lite" program that is on the main page be able to un smile the horizon and bend it back so it looks flat? It is only 40 bucks so I think I will buy it and take the mirror off by bathroom door and do some expirimenting. I already have a projector mounted to the cieling in the center of the room and a small mirror on the wall above the overhead so all I need to do is put a piece of white paper over the existing mirror and re focus the image on the paper then mount the large mirror in front of the sim.

Now that I am imagining this what about a curved screen, the one behind you, also bieng tipped at an angle might be able to curve the horizon the other way cancelling out the curved horizon on the big mirror?

My bathroom mirror is only about 18" wide by about 5 feet tall and is glass so I can't bend it much, but enough to test the concept. I will report my results tomorrow.

Andy Smith

Mike.Powell

10-18-2010, 06:09 PM

Neilh has a good point about a WAC style collimating display being easier to make. Here's some hopefully useful information.

WAC stands for wide angle collimating display. The name is something of a misnomer today, but when introduced it was a step up on the competition.

Imagery is produced on a CRT mounted above an angled beamsplitter. Light reflects off the beamsplitter to the collimating mirror before finally getting to the viewpoint.

http://www.mycockpit.org/photopost/data/536/wac.jpg

Depending on design choices, this approach provides on the order of 50 degrees horizontal field of view and 35 degrees vertical field of view. Adjacent units, angled in toward the viewpoint can provide panoramic imagery.

The mirror has a spherical curve. It should be much easier to make (or buy) than the film mirrors used in cross-cockpit collimated displays.

Glass Mountain Optics makes large optical elements for simulators. Several years ago they advertised on their website that they made lower cost mirrors for museums and hobbyists. Since then they were acquired by FlightSafety International. I don't know if GMO still offers products to the general public, but maybe they do.

A few years back I ran across a posting about having a spherical section mirror made by a firm that makes the hallway safety mirrors. It was a special order, but all they did was put the reflective layer on the other side, i.e. making a concave mirror rather than their normal convex products. If I can find more details I post them later. [edit: I think this was the company: http://www.campuscrafts.com/]

US patent #3,549,803 "Virtual Image System for Training Simulator" describes a method for making spherical film mirrors using reflective Mylar, urethane foam and fiberglass.

US patent #4,822,155 "Mirror Assembly with Flexible Membrane" describes the construction details of a large diameter, spherical-section film mirror. University of Strathclyde built a number of these mirrors for their use in research projects. They use reflective Mylar. As Matt pointed out, Mylar is tough stuff that takes a lot of force to stretch. The method of mounting the film is an important factor in the optical quality of the finished mirror. This patent details one approach which has been shown to work well.

It may be possible to use sun control window film as a low cost beamsplitter. A more expensive option is available from Teleprompters.ws They sell properly coated glass beamsplitters with the partially reflective coating on one side and an anti-reflection coating on the other to reduce ghost images.

To avoid image distortion and other problems, the faceplate of the CRT should has a spherical shape of one half the radius (or slightly more) of the collimating mirror. It also needs to put out a lot of light. CRTs of this shape are no longer available. A rear projection screen is the contemporary replacement. If you project on-axis with the proper throw ratio, the majority of the projection-related distortion vanishes.

Because of the multiple reflections and the 50% beamsplitter, at most 25% of the light from the screen makes to the viewpoint. 10~15% is more likely. You need a lot of light. The old CRTs were special units pushing 50 to 100 foot Lamberts. A pico projector won't do, but a regular projector should.

I think the value in a collimated display is the promise for greater immersion. It makes the world outside the sim window look bigger, and adds realism. I think the cross-cockpit off-axis collimated system would be best because it provides an unobstructed view with considerable allowable head movement. The WAC system can provide a panoramic view by sticking multiple units side by side, but this leaves structure in view and limits allowable head movement. That said, the WAC approach may be the best, workable approach available at present.

Mike.Powell

10-18-2010, 06:37 PM

Acrylic mirror material does not tolerate heat well. Once you get it hot enough to bend, the reflective coating is toast. I've tried.

Neil Hewitt

10-19-2010, 06:21 AM

A few years back I ran across a posting about having a spherical section mirror made by a firm that makes the hallway safety mirrors. It was a special order, but all they did was put the reflective layer on the other side, i.e. making a concave mirror rather than their normal convex products. If I can find more details I post them later. edit: I think this was the company: http://www.campuscrafts.com/

Yes - their rectangular convex mirror looks like a section of a sphere; get a 36" one of those and have them silver the other side, you might be in business. That'd create a WAC unit wide enough for one window of a B737 sim. Make the join directly at the edge of the mirror, assemble a few units together, and you'd have something useful. Not much vertical FOV, though.

I'll see if I can find someone similar in the UK. Got to be worth a try, even just as an experiment.

Matt Olieman

10-19-2010, 09:45 AM

Please keep in mind, this works well with curved monitors not flat screen. Flat screen will cause blurry edges. Also, some CRT's do not work well when the screen is facing down.

Matt Olieman

Neil Hewitt

10-19-2010, 10:39 AM

True, but the standard replacement for the CRT in a WAC (or cross-cockpit display) is to use a projector + curved rear-projection screen as the picture source.

Alternatively, perhaps a correctly-focused collecting fresnel lens in front of a TFT could create the same optical effect as having a curved CRT screen.

wledzian

10-20-2010, 06:37 PM

I've been reading through several patents related to design, manufacture and installation of cross-cockpit collimated displays. A few things I've learned:

The mirror is typically made from Mylar film (we knew that already)
The film is held in shape by vacuum. It is supported only at the edges, and is not glued to any backing.
The applied vacuum is typically dynamically controlled via a feedback loop and position sensors located behind the mirror.
A certain amount of distortion will be present due to uneven stress within the mylar film. Most of this distortion occurs near the corners, and can be partially mitigated by methods described in several of the patents.
While high-school level physics usually teaches that "the focal plane of a sphere is at R/2", this only applies for significantly on-axis rays. In a cross-cockpit display, the eyepoint is far off-axis, and aberration must be taken into account. Due to this, the radius of the projection screen is significantly larger than R/2.
Due to the details of the optics, vertical FOV over 40 degrees is difficult to achieve. The vertical FOV distribution (ex. 20 deg up/ 20 deg down or 10 deg up/ 30 deg down) can be set by design choices..
Horizontal FOV can be as wide as you like, limited only by the available width (length is practically unlimited) of the mylar needed for the large mirror.
Mylar film in widths greater than 56" is hard to find.

Matt Olieman

10-20-2010, 07:20 PM

Excellent article by Mike Powell on the home page regarding Collimated Displays.

Thanks Mike :) :) :)

Matt Olieman

Mike.Powell

10-20-2010, 09:56 PM

mikesblack

10-20-2010, 10:13 PM

wledzian,

Great post!

Can you post a link to the patent site that describe the methods for correcting corner distortion?

I'm also interested in the method of vacuum regulation via feedback. I wonder if this is critical for maintaining of the image on a flight on an ongoing on demand basis or for keeping the Mylar tension and thus the image from degrading over a longer time. If it is the later, I wonder if one can build in some mechanism to regulate tension, like tuners on a guitar. I imagine one would need to have an idea of the practical requirements for keeping that Mylar in tune and set these adjustments at the correct intervals.

Thanks,
Mike

castle

10-20-2010, 11:36 PM

Great posts from Mike and wledzian. I was wondering about that R/2 question as well.

The original video from the discovery segment seemed to show a projection screen that was (at least based on a visual observation) larger than the R/2 ratios and extended beyond the top of the cabin windows so as to avoid any shadowing problems.

If you go back to the basic physics of optics and collimated mirrors, anything inside the focal point will appear upright and larger than the object, in this case the projection screen, and will be a virtual image.

As Mike noted, the need to warp the image to handle the distortion requires aspheric lenses and those are not cheap, as in thousands of dollars. This is going to be a major hurdle.

JW

Mike.Powell

10-21-2010, 12:49 AM

I've been using TurboCAD to do ray tracing. It's a little cumbersome, but I believe it to be accurate. I'm not using the paraxial approximations. Rather, I trace reflections based on the law of reflection (angle of incidence equals angle of relfection). The idea is that when a ray hits the mirror surface, I draw a line from the mirror center to the point where the ray intersects the mirror. I then draw the reflected ray to match the incident ray angle. It requires a bit of middle school geometry construction, but it appears to work. The results I'm getting are similar to the optical configuration in the 1982 NTIS report "Wide-Angle, Multiviewer, Infinity Display System".

For an off-axis system, the screen surface shifts closer to the mirror with the top tilting even closer. While a vertical cross section through the screen is still a circular arc, its center shifts toward the screen while the vertical axis of revolution stays with the mirror center, so the screen surface becomes toroidial or oblate (slightly squashed)

As far as image distortion goes, I'm hopeful that image warping software like Nthusim will be the solution. A requirement for color-corrected, aspheric projection lenses would make the project impractical.

A possibility is front projecting the screen using a second spherical-section mirror as a fold mirror. Possibly, this would resolve some or most of the projection distortion.

Matt Olieman

10-21-2010, 07:31 AM

Just some pics you may find interesting: :)

Matt Olieman

http://mycockpit.org/images/collomating-mirror/B1sm.jpg
http://mycockpit.org/images/collomating-mirror/http://mycockpit.org/images/collomating-mirror/B1sm.jpg
http://mycockpit.org/images/collomating-mirror/FS drawing Layout.jpg
http://mycockpit.org/images/collomating-mirror/Image Generators floating_collimated.jpg
http://mycockpit.org/images/collomating-mirror/Image Generators retrofit.jpg
http://mycockpit.org/images/collomating-mirror/Image Generators vs_components_cut_away.jpg
http://mycockpit.org/images/collomating-mirror/INTELX_Citation.jpg
http://mycockpit.org/images/collomating-mirror/Jet Sim 3368f2-r.jpg
http://mycockpit.org/images/collomating-mirror/MV-22A_CH-53E_CH-46E_domes.jpg
http://mycockpit.org/images/collomating-mirror/MV-22A_HTI_OFT_dome.jpg
http://mycockpit.org/images/collomating-mirror/NASA rfd7.jpg
http://mycockpit.org/images/collomating-mirror/WIDE Projection System.gif

wledzian

10-21-2010, 10:42 AM

I don't have a list of the patents handy and time is short at the moment, but I'll pull the list together and post it tonight.
The patents don't give any real insight into the shape of the screen. Most of them state something along the lines of "this invention comprises a rear-projection screen of spherical shape, generally 1/2 the radius of the collimating mirror" or similar. Several patents even go so far as to specify non-spherical shapes (sections of ellipse or toroid), but continue to perpetuate the falsehood of a radius substantially half of the mirror.

I've also put together an Excel spreadsheet to play with geometry. In essence, I cast several sets of parallel rays from a prospective eyepoint, and let Excel do the math to see where each set converges. These points form the shape of the mirror surface. Ponts on this line will be collimated at infinity, at the selected eyepoint. Points on a surface of larger radius will appear to be closer to the pilot. As long as the virtual image is more than 30 feet out, monocular depth cues will dominate.

The shape of the screen is strongly defined by the chosen eyepoint and size of the spherical mirror.
The bottom edge (and therefore lower limit of vertical FOV) is limited by the highest sightline from the eyepoint. This is the limiting factor in the restricted vertical FOV.
The TOP of the screen has no such restrictions, and extending the top of the screen allows the pilot to lean forward and look upward. As long as the cockpit structure has a more restrictive lower vertical limit than the display, the pilot won't see the bottom edge of the mirror, and the illusion will be maintained.

castle

10-21-2010, 11:57 AM

mikesblack

10-21-2010, 01:34 PM

"I've been reading through several patents related to design, manufacture and installation of cross-cockpit collimated displays. A few things I've learned:
• The bottom edge (and therefore lower limit of vertical FOV) is limited by the highest sightline from the eyepoint. This is the limiting factor in the restricted vertical FOV." from wledzian

Thanks again wledzian. I really appreciate your insights in this.

In regard to the mirror's bottom edge, I am trying to figure out the radius to use and also the lower edge location. I want to place the lower edge higher than the sim floor, perhaps a foot or so below the cockpit windows. This would set the bottom of the arc, or bottom of sphere above the cockpit floor. The rational is to have the mirror set close to the sim, as space is an issue in my room, while capturing a full range of view.

I have cut a couple of sections of arc, 5 and 6 feet respectively that are 30 degrees each. I want to get a general idea how much space will be used by placing these cut arcs next to the windows, look outside and make sure I don't see the borders.

Given the examples that I have seen on pro simulators, the mirror edge seems close or at cockpit floor level. I wonder if by raising the sphere vertically as I have described, I would be making the mirror unworkable. Best to know ahead of time before plunging in.

mikesblack

10-21-2010, 01:38 PM

Few interesting links:

Matt,
How can I upload an image (jpeg) here?
Mike

http://www.q4services.com/links.php
http://www.simulation.org.uk/register.php

Mike.Powell

10-21-2010, 02:46 PM

Mike,

The image when the object is between the concave mirror and focus is a virtual image formed behind the mirror. Does the program allow you to extend the ray to a point behind the mirror where the image "exists"? Supoose you could do that manually but so much nicer if the program did it. ;-)

JW

TurboCAD allows line extension. Select the line and drag as far as you want. TurboCAD also provides a means to measure the angle between two line segments. It draws a circular arc centered on the intersection point even if the segments have not been drawn long enough to intersect. It's a quick and dirty way to see where the image falls, as well as, what the angular collimation error is.

This is undeniably clumsy, but it seems to work. I've been developing graphical techniques for locating the top and bottom edges of the mirror given the field of view requirements and viewpoint location. It also lets me know where the screen should be and what the shape is. I've been using the pro version of TurboCAD, but I expect the free version of DoubleCAD XT would work as well.

OSLO is a professional optical design tool available in a free student version. It's another possibility, but I haven't taken the time to learn how to use it.

wledzian

10-21-2010, 02:48 PM

Given the examples that I have seen on pro simulators, the mirror edge seems close or at cockpit floor level. I wonder if by raising the sphere vertically as I have described, I would be making the mirror unworkable. Best to know ahead of time before plunging in.

So much to say, so little time during lunch break...

Here's a quick sample from my raycasting simulation.

The dark blue circular line is the mirror. In this case, radius is 48 inches.
Magenta lines represent the cast rays. Vertical FOV is 10 deg up, 30 deg down. Eyepoint is located 20 inches below the center, offset 4" forward to represent the offset of my eyes from the vertical rotation axis of my head. For this simulation, I've used a parallel ray offset of 1". Due to the shape of the mirror generated by these parameters, this geometry may not be achievable for a full 180 degree horizontal FOV unless I can find a reasonable source of mylar film in larger widths.
Black dots represent the screen for convergence at infinity. A screen surface inside these points will not properly form a virtual image when viewed from the design eyepoint.
Blue dots represent the screen for convergence at 30 feet. A screen surface outside these points will produce a virtual image closer than 30 feet, partially defeating the purpose of collimation.
The yellow line represents a spherical screen at the minimum radius required to form an image over the full field of view. As you can see, a screen of this shape would further restrict the achievable vertical FOV and would cause the lower half of the image to appear too close. It also serves to illustrate the oblate spheroid nature of the 'proper' screen shape.

http://www.mycockpit.org/photopost/data/500/raycast.JPG

Given the examples that I have seen on pro simulators, the mirror edge seems close or at cockpit floor level. I wonder if by raising the sphere vertically as I have described, I would be making the mirror unworkable. Best to know ahead of time before plunging in.

The commercial sims typically have a mirror radius between 9 and 11 feet, and have a much larger horizontal offset applied to the design eyepoint. If you provide a bit more information about your sim, I can crunch some numbers for you.

In designing my sim (still in the design phase), I started with the space I could get away with taking up, chose a field of view based on desired over-the-nose visibility in the pattern and on approach, and designed the cockpit interior based on the space remaining. My cockpit will be a single-pilot generic pit, as I'm finding that the bottom edge of the 48" mirror is driving the location of my instrument panel, and would not be usable for a cockpit sized for two pilots.

I won't be home until rather late tonight, I'll get that list of patents put together tomorrow morning.

Matt Olieman

10-21-2010, 03:06 PM

Few interesting links:

Matt,
How can I upload an image (jpeg) here?
Mike

You can either attach it to your post or what would be better; post it in the Photo Gallery and link the image to it there. When you look at a image in the "Photo Gallery" you'll see near the bottom "Direct link:" That would be the link to your image.

Hope that helps. :)

Matt Oleiman

mikesblack

10-21-2010, 07:07 PM

Thanks Matt. That does.

By the way, has anyone seen this ?

http://www.doti-optics.com/PERMA%20%C2%AE%20Mirror.htm

mikesblack

10-21-2010, 08:24 PM

Thank you very much indeed. Your help and advice is most appreciated.

The following are the dimensions that I am working with.

Width of sim at widest point(rear) :11 feet.

Measurement from port rear of cockpit to wall: 23 inches.
Measurement from starboard rear of cockpit to wall: 18 inches.

Sim frame slopes in from rear to nose and so the above measurements are the most restrictive.

Height of sim 73 inches at rear and slopes to 57 inches at the apex of the front windows.
Height from top of sim to ceiling is 41 inches at rear.

Length from back of sim to front( measured at apex of front window) 68 inches.
Length from throttle location to apex of front window : 24 inches
and 48 inches to the most forward part of front window.

- Note the recent photos I just submitted. There is a rope that is attached to the throttle location and held out at 5 feet. The curve that I have in the photos is 30 degrees and 5 foot radius.
http://www.mycockpit.org/photopost/showphoto.php?photo=6196&title=767-update-10-21-10&cat=690

mikesblack

10-21-2010, 08:25 PM

http://www.mycockpit.org/photopost/data/690/0231.jpg

castle

10-22-2010, 12:08 AM

Thought I posted this earlier, but don't see it. Apologies if this winds up as a double post.

In all the discussions on ray tracing and FOV are we actually considering what the pilot will see; i.e., where is the image, amount of distortion, image warping required, and where and how to actually position the mirror and projection screen?

Seems we need to also consider the two rules of reflection for concave mirrors:

Any incident ray traveling parallel to the principal axis on the way to the mirror will pass through the focal point upon reflection.
Any incident ray passing through the focal point on the way to the mirror will travel parallel to the principal axis upon reflection.

In order to do that we also need to specify the principle axis which sets the vertex of the mirror, relative position, orientation, and shape of the object (the screen), and location of the focal point which is on the principle axis at 1/2 the radius.

Need to think about it a bit more....

JW

castle

10-22-2010, 01:08 AM

In addition to the FOV another important calculation is the determination of the image formed by the screen and mirror geometry based on their relative positions to each other, the principal axis of the concave mirror that defines the vertex, the focal point, and radius of curvature.

Beat me up and call me crazy, but don't think the examples shown provide that solution. For that we need to apply the two rules of reflection for concave mirrors and incident rays;

* Any incident ray traveling parallel to the principal axis on the way to the mirror will pass through the focal point upon reflection.
* Any incident ray passing through the focal point on the way to the mirror will travel parallel to the principal axis upon reflection.

Performing that calculation(s) will help determine, in addition, the amount of image warping the software has to handle. Also assuming that the principal axis has to intersect the physical mirror and the horizontal axis will be symmetric for the entire 180 degrees and then one only needs to calculate the geometry for a single set of points on the screen in the vertical.

An important item to define is the vertex of the mirror which, in turn, lays out the principal axis and focal point.

This is really neat stuff. Kudos to mikesblack for starting the thread and to all who have contributed.

JW

Mike.Powell

10-22-2010, 01:26 AM

Film collimating mirrors are spherical-section. Those rules are accurate only for parabolic mirrors or for very shallow spherical mirrors.

wledzian

10-22-2010, 01:37 AM

@mikesblack: (Thanks Mike.Powell for the link to the photos) A full-size 767 cockpit - color me green with envy. When I get to work on Monday, I'll pull up the 767 ops manual and check out the eyepoint locations and field of view definitions. I will say that fitting a wide collimated display around that may not be possible in such a tight space. In the meantime, I'll work with guesstimates and see what I can come up with. ...And I haven't forgotten about the patent list.

@Castle: Those two rules only apply to an optical component that actually has a true focal point. A sphere does not have a focal point. While parallel rays very near the axis will converge to a small region around R/2, this does not hold true for rays significantly off-axis. Rather than a focal point, a spherical mirror has a "caustic focal surface". Parallel rays which are close enough together, say the diameter of your pupil, will converge to a small region somewhere along that caustic surface.
http://upload.wikimedia.org/wikipedia/commons/thumb/4/40/Caustic_of_a_circle.svg/500px-Caustic_of_a_circle.svg.png

Rather than using the simplifying assumptions of ideal optics, my calculations do in fact calculate the reflected ray vectors for sets of parallel rays (from a hypothetical virtual image at infinity), and calculates the focal point to be the average of their intersections. I can also set a specific image distance for the ray sets so that the cast rays from the eyepoint converge, and generate a focal point for a virtual image at a non-infinite distance. Those calculations are used to generate the points for the limiting surfaces for images at infinity and 30 feet in my earlier post.

castle

10-22-2010, 11:19 AM

Dug out my old drafting set and went crazy trying to come up with some diagrams using the aforementioned reflection rules. Nothing seemed to work and what worked wasn't buildable or useful.

So my understanding is you are working from where you want the image to be and then defining the projection screen (location and position) based on the mrror size.

Thank you for the explanation.

JW

wledzian

10-22-2010, 11:45 AM

Some of the applicable patents:

Aspheric screen for collimated visual display apparatus
http://www.google.com/patents/about?id=7zoWAAAAEBAJ&dq=6944581

Method of constructing a thin film mirror
http://www.google.com/patents/about?id=N8cQAAAAEBAJ&dq=6758569

Apparatus for constructing a thin film mirror
http://www.google.com/patents/about?id=orYVAAAAEBAJ&dq=6945659

Collimated visual display with elliptical front projection screen
http://www.google.com/patents/about?id=D3vQAAAAEBAJ&dq=12/273,053

Method and apparatus for modifying aircraft simulator wide-angle infitiy display equipment mirror to enlarge field of vision and for reskinning aircraft simulator spherical mirror cell to minimize mirror stress and distortion
http://www.google.com/patents/about?id=ZOrOAAAAEBAJ&dq=7708561

wledzian

10-22-2010, 11:51 AM

So my understanding is you are working from where you want the image to be and then defining the projection screen (location and position) based on the mrror size.

Thank you for the explanation.

JW

You're welcome.
I'm doing exactly that, point-by-point, for enough points to sufficiently define the screen shape.

wledzian

10-22-2010, 08:53 PM

@Mikesblack:
I took a stab at putting a mirror around your cockpit. I figure you could shoehorn an 84" radius mirror in the space you described, so I started there. I located the eyepoint in a freeware model of a 767 in Sketchup, and set the mirror in place to get a first-shot eyepoint. This first try gives a 180° horizontal FOV and nearly 75 degrees vertical. The mirror geometry intersects the aft windows, so I couldn't swing the HFOV wider.
http://www.mycockpit.org/photopost/data/500/medium/mikesblack_MirrorStudy.JPG
http://www.mycockpit.org/photopost/data/500/Mikesblack_Mirrorstudy_firsttry.jpg

If you're willing to sacrifice some of your vertical FOV (a permanently installed "sunshade" should suffice), you can move the whole mirror assembly aft and get the HFOV to cover all the windows. I haven't worked up the geometry for that yet.

So far, that covers the "is it possible" aspect. There are, however, several large roadblocks:

The forward structure of the cockpit below the windows interferes with the lower mirror edge. This makes mounting of the mylar challenging.
The mirror would require a single piece of mylar sheet over 13 feet wide and almost 30 feet long. I haven't been able to find a supplier willing to sell me less than a full production roll for sizes over 56" wide.
The screen itself is over 10 feet wide, posing its own challenges simply finding raw material for forming.

I can play with mirror placement if you'd like, but the long and short of it is that the optics for a jumbo jet simulator are going to be a bit large to fit in a bedroom.

Mike.Powell

10-22-2010, 09:51 PM

There are a few other issues to keep in mind as well.

Mylar is elastic, but with a high spring constant. To stretch it, you must pull hard, and it will pull back. With a large mirror, you have a lot of Mylar putting stress on the frame. You need a structure capable of accurately maintaining its shape while supporting perhaps several hundreds pounds force.

Mylar is elastic up to a point then it deforms permanently. If the mirror is too deep, the Mylar must be stretched more and is more likely to be pushed outside its elastic region. When this happens, it won't happen uniformly across the film. Over-stretched Mylar has different properties than Mylar that has not. The distribution of tension across the Mylar is very much not uniform, and the shape is no longer spherical. The optical properties of the mirror are damaged. Much of the recent work on film mirror seems to have been focused on dealing with this.

wledzian

10-22-2010, 10:05 PM

That's good info Mike. I'll add a strain estimate to my spreadsheet to display a warning if the strain is outside the elastic region of Mylar's stress/strain curve.

mikesblack

10-23-2010, 01:47 AM

Wow,
That is the most awesome thing you have done. Thank you very much for that. The diagrams are great.

I will need to study the diagrams for a while to get a better understanding and will reply in time.

Also, those patents are most helpful and have provided me with good sense for the construction. I will need to study these further and then will most likely experiment with smaller sections.

Again, most appreciated.

Mike

crashdog

10-23-2010, 09:07 AM

Hi,
didn't see this thread before just now, so I'm still reading through.
I have experimented a lot with plexiglas and mylar to make collimated displays. Some year ago I also made a little beamsplitter visual with a normal plexiglas as beamsplitter and a normal mirror on the backside. That works when it's dark enough in the room. offcourse it will work bether with a real beamsplitter. The best company I found for such mirrors in europe is seco-sign. You can choose how much the mirror should reflect from 5 to approx 20%.

I have also asked several plexiglas specialists here in swizerland if they could form such a spherical shape. The closest I got was one company that makes "bubble-windows" of plexiglass. But they can make max 1m diameters. So to small for a visual. They told me that to make a shape in the magnitude for such a visual plexiglas would be around CHF 20'000.- (that's currently also about $20'000.-) That's just for the form. Mirror coating the formed plexiglas will probalby add another $ 5'000 to 8'000. Each.

So a spherical collimated visual will probably be to expensive or to technical difficult for me. Even just to make the backprojection screen spherical.
What I have started to experiment with some time ago is to make the "collimated" display conical shaped instead of spherical. It's much easier to shape. No heat needed. For the plexiglas mirror and the backprojection screen.
I use an opal white 3mm thik, with 90% light admission as a backprojection screen. The mirror is also 3 mm thik.
http://www.md80.ch/index.php?option=com_content&view=article&id=69%3Avisual&catid=34%3Asimulator&Itemid=1
This setup is still very experimental. Important is that, this will have a horisontal disortion that needs to be corrected. I use NEC NP901w projectors. They have a software to correct geometry dissortions directly in the projector. So no need for extra CPU consuming software on the pc.

I was wondering, has any one ever asked for prices at those companies like q4services or glassmountain ?
Especially glassmountain always stess their low-costnes. But I guess that very relative. But even if just the backprojection screen would be in a payaple price range would help a lot for a real collimated setup. http://www.glassmountain.com/Simulation/DualEyepointDisplays

Cheers,
Gery

geneb

10-24-2010, 11:49 AM

wledzian and I got some good work done on Saturday. We're getting closer. :)

I'm going to try to get the framework I have finished off with interior supports and a sealed back this coming week or so.

g.

Neil Hewitt

10-24-2010, 01:50 PM

So a spherical collimated visual will probably be to expensive or to technical difficult for me. Even just to make the backprojection screen spherical.
What I have started to experiment with some time ago is to make the "collimated" display conical shaped instead of spherical. It's much easier to shape. No heat needed. For the plexiglas mirror and the backprojection screen.
I use an opal white 3mm thik, with 90% light admission as a backprojection screen. The mirror is also 3 mm thik.
http://www.md80.ch/index.php?option=com_content&view=article&id=69%3Avisual&catid=34%3Asimulator&Itemid=1
This setup is still very experimental. Important is that, this will have a horisontal disortion that needs to be corrected. I use NEC NP901w projectors. They have a software to correct geometry dissortions directly in the projector. So no need for extra CPU consuming software on the pc.

So a non-spherical section mirror with correction does work - or at least provides enough focal distance to trick the eye into seeing through the plane. A conical section mirror like that is easy enough to do with acrylic mirror sheet. Fantastic that someone has already done it!

Looks like this may be the way to go with my project - my limited front projection room becomes much less of an issue and I could probably get 140 degrees out of my 16:9 projector.

It'll be fun experimenting :)

castle

10-24-2010, 01:56 PM

56" Mylar would provide a 45 degree FOV for a 6 foot mirror --- (45/57.2957)*72.0 = 56.548

OK, so we're a half inch short ;-) but close enough. You can get that size in very large lengths.

A 7 foot system would provide ~ 40 degrees vertical FOV. Still not bad for a DIY and you can't beat the price.

@wledzian. I would like to try and equip my 747 with a six foot mirror. What would you need from me in the way of data to crunch some numbers. Fortunately, have a little more room and a single available stall in my garage shop, but 6.5 radius is the upper limit and 6 leaves a little wiggle room.

Nice work.

JW

Mike.Powell

10-24-2010, 04:09 PM

Here is a simple graphic approach to designing and analyzing an off-axis collimated display.

A key step is tracing a ray path as it is reflected by a spherical surface. This draws on some middle school geometry and works well with drawing packages like TurboCAD that have line and circle tools with "snap to intersection" options.

1 - Draw a line from the mirror center to the intersection point of the incident ray with the mirror.
2 - Draw a circle centered on that intersection point. The radius is doesn't matter.
3 - Draw a second circle centered on the intersection of the first circle arc and the line from the mirror center. Set the radius at the intersection between the incident ray and the first circle arc.
4 - Draw the reflected ray from the intersection of the mirror surface and incident ray to the intersection of the arcs of the two circles opposite the incident ray.

http://www.mycockpit.org/photopost/data/536/reflect.jpg

Laying out the positions of the collimating mirror, screen, and viewpoint starts with estimates. Because this is an off-axis system we know that the screen will be larger that the textbook, on-axis figure of half the mirror radius. We'll start with 65% of the mirror radius. We'll place the viewpoint directly under the mirror center of curvature down 50% the mirror radius. The viewpoint doesn't have to be directly under the center, but this position provides the most symmetrical viewing for a single person system, and presumably the smallest geometrical image distortion as you turn your head.

1 - Draw circular arcs representing the mirror and screen surfaces.
2 - Draw lines from the viewpoint representing the upper and lower limits on the vertical field of view.
3 - Reflect the lower field of view up to the screen surface. This is where the lower edge of the screen needs to be for the current estimated position of the viewpoint.
4 - If the screen edge is below the upper field of view limit, the viewpoint is too high. Move the viewpoint lower and try again. If the screen edge is far above the upper limit, move the viewpoint higher and try again. If there is enough space between the lower screen edge and upper FoV limit for the screen framework you haven't designed yet, proceed to step 5.
5 - Reflect the upper FoV limit to the screen. If the reflection misses the screen, the upper FoV may not be possible. Before giving up in dispair, move on to screen placement refinement.

http://www.mycockpit.org/photopost/data/536/collimated1.jpg

The screen shape and placement is an estimate. Almost certainly you'll want to tweak it. Do this by using parallel test rays that bracket the viewpoint. Reflect them off the mirror to the screen. Their intersection point should be on the screen surface.

1 - Draw two parallel horizontal lines from the viewpoint to the mirror arc. One line should be above the viewpoint, the other below.
2 - Reflect both lines from the mirror. Extend the lines until they intersect.
3 - Draw another pair of parallel lines bracketing the viewpoint to the mirror. These lines should angle downward at the lower FoV limit. Reflect and intersect.
4 - Repeat the process with lines angled at the upper FoV limit.
5 - These three intersection points define a circular arc which is now a very good estimate to where the screen surface should be. The center of this arc is unlikely to be the same as the center of curvature of the mirror. The new screen center will probably be closer to the mirror surface and higher than before. The net effect is to produce a screen that bulges out more and has a top that leans in toward the mirror.

http://www.mycockpit.org/photopost/data/536/collimated2.jpg

You will probably need to make several passes through the whole process to converge on a configuration that meets your needs.

Once you have a workable configuration, you can ray trace diverging paths from multiple points on the screen surface to check for collimation accuracy.
I used TurboCAD, but I think you can do the same thing with DoubleCAD XT, a free program.

wledzian

10-24-2010, 04:55 PM

@castle -
Could you provide a little more info regarding the numbers in that formula? Do you want a wraparound section of a cone? It's the flattening of the conic surface that pushes an otherwise workable mirror height past the available material width. If the conic surface works well, the issue of a monolithic surface may be moot, as joined gores would suffice without introducing issues of distortion due to uneven stress and potential weak points at the seams.

@crashdog -
I'm intrigued by your use of a conic surface mirror and screen. That would certainly be easier to fabricate than a vacuum-formed spherical surface. The horizontal movement of the camera seems to show a distant image, but I'm concerned that the optical properties of a conic surface would introduce significant astigmatism to the image. How does the effect hold up for vertical movement?

@geneb -
Thanks for having me over on Saturday. I have a sense that as many questions were raised as were answered, but it feels like there's some progress. If we can mange to get a mirror formed to your existing frame, it should work well for a 30 degree VFOV with a couple inches margin left over at the top and bottom to take up any residual distortion in the material (3 inch horiz offset, 18 inch vert offset, 75° top angle, 105° bottom angle, convergence at 30 feet). I have a feeling that the following two patents together may offer a solution for mounting the mylar without having to stretch it in the process.
http://www.google.com/patents/about?id=ipJ7AAAAEBAJ&dq=6050692
http://www.google.com/patents/about?id=orYVAAAAEBAJ&dq=6945659

crashdog

10-24-2010, 05:45 PM

I don't have any math. figures at the moment. The impression I got from my experimental setup is that vertical movement is no problem as long as the angle of the backprojection screen is the same as the angle of the mirror. But the setup has to be dainly precise. Otherweise the picture looks really weird. But I guess the seame issue would be for a spherical setup.

Gery

geneb

10-24-2010, 05:49 PM

It was fun and educational. :)

I'm sure we'll get it sorted - it's pretty much down to a mechanical process right now.

g.

castle

10-24-2010, 06:37 PM

@Mike

Nice diagrams! Not being an optics guy, I'm puzzling over your comment regards the single viewer position and image distortion as you turn your head.

My understanding of a collimated display is that the image viewed is irrespective of position and the sight line from the "lookers eye" to the frame edge of the cockpit window describes the boundaries of the FOV. The image will not "change" if I move from the left seat to the right or get up and walk to the cabin door, just that portion of the image that I see.

If that is true then the purpose of your directions is only to establish a point of reference from which to start the design for mirror/screen geometry and relative placement. Is that correct? And distortion is a property of the projection system, lenses, warping software, geometry tolerances, and other artifacts when moving from the theoretical world to reality.

Perhaps should have asked via PM, but hopefully others will gain from this discussion.

JW

Mike.Powell

10-24-2010, 07:12 PM

Collimation with a spherical mirror is good, but not perfect.

If the viewpoint is directly under the mirror center of curvature, looking left or right makes no difference. The vertical cross section through the viewer, mirror and screen is the same regardless of lateral viewing angle.

However, if the viewpoint has been shifted forward, perhaps to allow greater vertical field of view (or sideways to fit in a copilot), the vertical cross section including the viewer, mirror and screen is skewed when the viewer looks to the side. The optical paths are longer and the angles different. So, collimation is probably less accurate, and the image is more distorted.

Optimizing a wide-angle collimated display is a tradeoff between many factors.

castle

10-25-2010, 11:42 AM

@wledzian
Wasn't quite sure of your question regards numbers in the formula. Could you provide a bit of clarification?

JW

wledzian

10-25-2010, 12:01 PM

56" Mylar would provide a 45 degree FOV for a 6 foot mirror --- (45/57.2957)*72.0 = 56.548

The 45 is obviously 45 degrees. Is that vertical or horizontal?
I'm assuming that 72 is inches, equal to 6 feet.
What do the other values represent?

castle

10-25-2010, 02:47 PM

The 45 is obviously 45 degrees. Is that vertical or horizontal?
I'm assuming that 72 is inches, equal to 6 feet.
What do the other values represent?

The 45 is the vertical and 72 is the radius of curvature ( 6 feet ).

57.2957 is a radian. A constant used to convert degrees of arc to a linear value. Circumference of a circle is pi*diameter.

or 360 degrees = 3.1415 * 2 * radius

rearranging terms 360 / ( 6.283048) = radius or

the distance along the circumference of a circle equal to the radius is 57.29703 degrees of arc.

By the same token 180 degrees horizontal for a 6 foot radius requires 18.849 linear feet of mylar material (180/57.2957)*6

As you noted, this would be slightly off for something of a flattened arc and does not include the margin required to fastened the mylar to the surface.

JW

Mike.Powell

10-25-2010, 03:50 PM

The material when flat takes the shape of a truncated cone which has been unrolled. There is significant curvature to the top and bottom edges. The impact is that the width of the required flat rectangular stock is much wider than the vertical chord of the mirror surface.

One very quickly runs up against limits of available material width.

wledzian

10-25-2010, 05:45 PM

@Mike.Powell, (cc)geneb:
One challenge Gene and I ran into was the vertical pre-stretch required simply to fit an unrolled cone to the 60° frame. We also tried using the vertical arclength instead of the chord; this fit the frame a bit easier, but would still require more horizontal stretching near the mid-lattitudes than is available by cutting across the horizontal chord. Something considered but not yet tried due to lack of time on Saturday was introducing an arc to the vertical edges to take up some of this gap. Even if we can eliminate some of the prestretch by this method, I'm still concerned that the uneven strain in the horizontal direction combined with near zero strain in the vertical direction will prevent the formation of a spherical surface.

In your research, have you come across any mention of ways to mitigate these issues during mirror fitting?

Mike.Powell

10-25-2010, 06:48 PM

There are a few methods mentioned.

The horizontal arc of the framework can be extended with the vertical side made straight so no vertical stretch is required during installation. The extended mirror area is useless optically and is masked off.

The vertical framework sides can be made flexible so that the film can be installed with no stretch. The sides are cranked into a curve after film installation.

Temporary, straight frame extensions can be fastened to the frame for film installation. Once the film is vacuum stretched into shape, the vertical sides of the film are clamped to the curved frame sides, the film is trimmed, and the extensions are removed.

The frame sides can be extended with circular arcs which are on a plane which blends with the unstretched conic section of the film as shown below.
http://www.mycockpit.org/photopost/data/536/pat6050692image1.JPG
This is from US patent 6050692. I think this has the best chance of success of any hobby approach. It appears to not require stretching during installation, only that the film be pulled taut.

The film tension is not uniformly distributed. I don't think you want it to be. The center horizontal band must stretch the most as it is at the deepest portion of the curve. The top and bottom edges have been cut to the correct length to be on the spherical surface without stretching, so you don't want any horizontal tension there. Vertical tension should be uniform across the whole surface, but of course it won't be at the sides, but the circular arc side additions provide a smooth transition from frame side support to active mirror surface.

I think this produces a satisfactory optical surface as long as the film stays in its elastic region. Once the film stretches beyond its elastic limit, it becomes necessary to prestretch horizontally at the top and bottom. I think this was a major issue in developing film mirrors for displays with vertical fields of view greater than 45 degrees. This probably means that DIY mirrors are limited to 40~45 degree vertical arcs if they are to be one contiguous piece. This may not be an issue due to the limitations on the width of mirror film stock.

Jordan Farmer

10-25-2010, 07:05 PM

Hey guys, umm, sorry to butt in here, ive read parts and im extremely confused, i dont understand this stuff, but, i saw on the Simquip website, that 2 collimating mirrors are for sale, i thought that this may be an appropriate place to mention it, if it hasnt been already ;) Heres the link anyway
Simquip Specials Page (http://www.simquip.com/Company/SPECIALS/SPECIALS.html)

Again, im sorry if i missed this before in the post!

Cheers, Jordan

Mike.Powell

10-25-2010, 08:01 PM

Thanks, Jordan.

Both timely and appropriate, IMHO.

mikesblack

10-25-2010, 09:41 PM

Weledzian,

Spent the last few days considering your diagrams and comments. I have also been reading the patents, and also Mike's additions.

While considering these many elements, the first and possibly most important is if I have the space required to do this. The thing I have done so far that gives me some hope is cut 6 curved pieces of plywood that is meant to fit just below the lowest point of my cockpit windows. This is intended to be the lower edge base for the mirror. My goal is to have this curve clear the entire structure to allow the rear windows to have full view. It turns out this curve is 5 feet 6 inches radius.

The arc radius will be greater than this 5ft 6, presumably 7 feet and as much vertical to allow for max 55 inch Mylar width limit. I'm thinking of 30 degrees. I'm considering as much adjustment as I can build in the better. I will use some tracking system that will allow adjustment of the mirror forward - aft and up and down, perhaps by several inches either way. I plan to do the same with the projection screen.

Beside the issues we are trying to better understand, e.g. clamping Mylar, I will need to be sure that I can walk through the narrow gap between the wall and the mirror and that the mirror can be set so as not to reflect the fuselage and but not set at such an angle to restrict passage.

Additionally, I was considering Mylar material. Do you know if there is much variance in quality? I was considering reflectivity and durability( scratch resistant).

Again, I want you to know how much I appreciate your help.

Mike

wledzian

10-25-2010, 10:36 PM

mikesblack,
No problem - this is fun!
I need a few more measurements:
I need to define the vertical axis of the screen and mirror. Where is your eyepoint with respect to the center of the 5'6" curved base?
I need to define the lower eyeline. Measured in a plane defined by the eyepoint and the mirror axis, what is the angle between horizontal and the edge of the lower edge base?

Mike.Powell

10-26-2010, 12:15 AM

I understand that the quality of mirror Mylar does vary. However, I've had very good luck with 2 mil Mylar from Tap Plastics, and I've just received a roll of 1 mil Mylar from Nielsen Enterprises which also looks good. It's coated on both sides and is nicely reflective. I haven't unrolled it, but what I see so far looks to be high quality. Nielsen sells in 56 inch widths.

Mylar as a base material is strong. The coating is rather fragile. If you crease the Mylar, which happens very easily, you get a permanent mark. The surface also scratches very easily. Your best bet cleaning it is with a soft cotton cloth. A paper towel will scratch.

crashdog

10-26-2010, 02:02 AM

just found this document about plexiglas forming.
http://www.plexiglas.com/literature/pdf/135.pdf

and this one
http://www.iss.infn.it/cusanno/public/PerFabio/mirrors.pdf

Gery

Matt Olieman

10-26-2010, 07:43 AM

Your best bet cleaning it is with a soft cotton cloth. A paper towel will scratch.

In addition, do not use cleaning products. If you need to wet the cloth use distilled water.

Matt Olieman

castle

10-26-2010, 12:02 PM

@mikesblack

Some one can check my math, here are a few numbers...

For a base radius of 5.5 feet and a vertical arc of 30 degrees down from the equator requires a radius at the equator of

5.5 / cos(30) = 6.35 feet

increase the vertical arc to 45 degrees and the radius at the equator is

5.5 / cos(45) = 7.78 feet for the same base radius

Working backwards, for a radius at the equator of 7.0 feet if you go down ~38 degrees the radius at this point is 5.5 feet.

Hope this helps you with your sizing.

JW

wledzian

10-26-2010, 12:17 PM

@castle
your math is right, but the geometry is wrong. Your numbers assume the eyepoint is located at the center of the mirror sphere. In the case of mikesblack's cockpit, the eyepoint will be offset both horizontally and vertically, thus my need for this information before I can give an answer.

castle

10-26-2010, 01:08 PM

wledzian

10-26-2010, 02:14 PM

Got it! But for a side-by-side seating you would still have to account for the right seat and make the compromise that both seats would be a tad off and just use the center of the TQ for the horizontal point?? Then vertically, the distance from some "average" eye point to the top of the mirror assuming that is the equator.

Is my understanding correct?

For the most part, yes. There is certainly accounting for the right seat. The center of the TQ does not have to correspond to the center of the mirror, and if space allows, should not correspond to the center of the mirror. Ideally, the eyepoints should be somewhat forward of the axis. This results in reduced distortion for both pilots, but leads to a larger mirror. For a cross-cockpit display on a 767 cockpit, the eyepoint is at least 21 inches off-center horizontally, assuming the mirror axis is directly between the pilots.

Vertically, the FOV is restricted by the optics. If you take a look at the raytrace plots I posted way back on pages 6 and 7, you can see that the lower eyeline in essence defines the upper eyeline by virtue of locating the lower screen edge, and that the upper eyeline does not necessarily correspond to the equator.

In Mikesblack's case, the design eyepoint is fixed by the cockpit. The horizontal offset is fixed by the 5'6" arc he's planning as his lower edge, and the lower eyeline is fixed by the angle to this arc. The mirror radius is a variable, limited by the 7' distance to the side wall, with the vertical offset defined by the selected mirror radius.
Once I have the limiting geometry, I can play with mirror radius to get the maximum vertical field of view. If the geometry allows, I may also be able to assume a larger base radius in order to move the axis rearward.

As you said, this is really neat stuff. Just in passing, looks like a short throw lens for the projection system can be had for around $600 in the el cheapo models. Don't have the numbers as to depth of field, focal length etc. For the really good stuff the price is a bit steeper; from $1700 to $2500 per lens. in either case you still have to deal wth keystoning for off-axis and image merging at the boundaries, front and rear projection systems.

There are short-throw projectors available in the $700 range already that would likely work well for the rear-projected screen. No need to spend $$$ on aftermarket lenses. If you're talking wide-angle (fisheye) lenses, your wallet may be better off projecting onto a security mirror, at least as a first attempt. Keystone correction is best done entirely in software, as correction will be necessary and it's better to do it all at once, rather than run the image through two extra processing steps.

I'm trying to get some estimates for bending acrylic for those of us not as skilled as geneb with tools. Will keep you all informed...

JW

Please do. The topic of forming the rear-projection screen came up on Saturday, and there was discussion of building a forming oven just for that purpose.

@geneb -
If it does come to that, I'd be more than willing to share the cost with you. It's looking like a screen for a 48" mirror could be formed from a single 4x8 sheet of plexi.

geneb

10-26-2010, 03:05 PM

[QUOTE=wledzian;111483
@geneb -
If it does come to that, I'd be more than willing to share the cost with you. It's looking like a screen for a 48" mirror could be formed from a single 4x8 sheet of plexi.[/QUOTE]

Building an oven to evenly heat a 4x8 sheet of material isn't an insurmountable challenge, but could certainly be an expensive one. I think we'd be better off building a three segment screen and have the projector seams align along the screen seams. I'm game either way, but if we're going to build an oven & vacu-forming table to that scale, we'd better come up with a use for it after we pull a pair of 24" radius screens off of it. *laughs*

(Now if I was an Evil Scientist type , I'd be tempted to see how well you can vacu-form people...Muahahaha!)

Oh who the **** am I kidding? Who wants to volunteer? *Evil Laugh*

g.

(mumbles unpleasant things about nanny-ware)

castle

10-26-2010, 03:39 PM

@wledzian

Ahhh! the fog is slowy lifting...

Since discussions seem to indicate that the projection screen is not a uniform sphere might it be easier to use a front projection system. Redifun builds a front projection system and that eliminates the problem of projector seams.

Makes the setup a bit more complex but doable.

JW

ANDYSMITH

10-26-2010, 04:53 PM

@geneb I think there still is a person at Thun Field that vacforms plexi airplane canopies. He has an oven big enough to walk in and the vacuum systems too. He is next to the prop shop and behind Atkins Rotary.

Andy Smith

crashdog

10-26-2010, 05:03 PM

I just got a reply from a professional visual system manufacurer. They told me that "low-cost" systems start at around half a million u.s. $'s. So sure is no option for a hobbyist ;) But at least now we know.

Gery

geneb

10-26-2010, 05:14 PM

That's good to know Andy. When we get to that point I'll have to find out how much he'd rent time on it. I certainly wouldn't need him to build the form. :D

Gery, "low cost" and "collimated display" is like "military intellegence". It's an oxymoron of the most extreme kind. :D

Having said that, keep in mind that with a hobby system, perfection is the enemy of good enough.

g.

mikesblack

10-26-2010, 10:23 PM

Hi wledzian,

The 5 foot 6 inch curved base may be too short in order to allow for adjustment. I may need to expand that by a few inches. I am using aluminum tracks to allow for front to back and up and down travel.
Eyes are 46 inches from the floor. More pictures and measurements to come.

http://www.mycockpit.org/photopost/data/690/031_2_.jpg

Mike

mikesblack

10-27-2010, 05:39 PM

I think I'm going to move my bed to another location. If I have a chance of doing this correctly, I will most likely need to build the mirror without the restriction of needing regular passage.

Check out my latest photos.. The captains front window has a green mark and a string cross between the vertical and horizontal point of view. From that point to the wall measures 48". The height of my eyes is 45-46".

The upper edge of the side window is 53"and 31" for the lower edge. The angle of these windows is measured at 65deg.

I am not sure what I need to do to make sure the lower edge of the image from the mirror clears the side windows and fuselage while looking from inside the cockpit. Any ideas that you think I might consider?

Thanks again.

castle

10-28-2010, 12:27 AM

Hmm, Mike's question on clearances got me thinking.

Have DoubleCAD installed, but not ready to delve in, so got out my trusty old drafting set.

Starting with a 6 foot radius set the eye point down 3 feet and in 6 inches, think I got a workable solution for a FOV of +25 and -20 except

1) the top edge of the screen is 20 degrees below the equator
2) the lower edge is 60 degrees down
3) which provides 40 degrees of mirror to view or a width of ~ 50 inches for the mylar
4) the approximate radius of the projection screen is 4 feet

but the radius of the lower edge of the mirrot is 6*cos(60) = 3 feet which is inside the cabin :-(

Going to have to go back and reread Mike's tutorial in msg #78

@mikesblack
you might consider a projection screen that overhangs the top of the cabin and build a mirror accordindly

wledzian

10-28-2010, 02:29 AM

@mikesblack
Is your cockpit a to-scale representation of a 767? It looks to me like 5'6" doesn't fit.
I've got the sketchup model, I can trace the eyelines to locate the bottom edge of the mirror. So far, the best I've been able to match castle's geometry puts the eyepoint about 5" off-center from the mirror axis; the 767 eyepiont is at least 21" offset.

I'd like to give a more encouraging response, but I need to rebuild the geometry and play with it a bit, I won't be able to give it any real attention until Saturday evening, I'll let you know what I come up with.

mikesblack

10-28-2010, 02:29 PM

I believe my cockpit is close to scale, but I'm sure there is quite some error considering that angles used have been created using multiple photos and not from plans. So while I believe there is error, and also a degree of asymmetry, I wouldn't think there was a significant difference. I'll elaborate a little and ask some questions to follow, so to make sure we both understand and are discussing the same things.

Can you explain what you mean by the "eyepoint offset" from the mirror axis? My understanding as of now is that the mirror axis is the center of the mirror sphere, situated in the center of the cockpit, located adjacent to the pilots' eyes, and set at 90 degrees to the cockpit floor. With this assumption, the Captains eyes are 1' 6" from this point.

The 5 foot 6 inch circle that I cut was based on what could fit just below the lowest edge of the cockpit windows, so that it would miss intersecting the rear windows. Other than that, it is an arbitrary figure. As it is now, this ring just fits as intended, but I believe in order to get more adjustability, up/ down or back and forth, I will extend this radius.

If there is any measurement, you need that I have omitted, please let me know and I'll let you know.

Thank you very much again for your expertise and your time helping me solve this. Please do take your time and convenience. Again, I must say I am greatly appreciative.

Thank you too Castle for your help and input.

By the way, moved my bed, so have tons more room forward of the cockpit, but still have to deal with those side walls. My wife has been great allowing me to do this, but I doubt she would be so if I suggested, tearing down these walls.
:lol:

wledzian

10-28-2010, 03:20 PM

767 Airplane Characteristics for Airport Planning (http://www.boeing.com/commercial/airports/767.htm)
See section 4, page 109. In my early model, I used this information to derive an eyepoint. I found a to-scale model of a 767 in the Sketchup library and took a section cut through a vertical plane offset 21 inches from centerline per the Boeing document. From this section cut, I extended the upper and lower eyelines through the window edge intersection with the section cut and took their intersection as the eyepoint.

The mirror axis for a cross-cockpit display should be set at 90° to the floor at some point along the aircraft centerline. In a full-scale cockpit with the mirror axis directly between the pilots, the minimum offset would thus be 21 inches. If the axis is located behind the pilots, the offset would be larger.

So far, my optical calculations have been based on a symmetrical field of view, centered around the mirror axis. My cockpit will be single-seat, and the only horizontal offset I'm allowing is to account for my eyes being forward of my neck. In that case, the optics are consistent throughout the horizontal field of view. In a two-seat cockpit, these optics calculations only hold true along a plane defined by the eyepoint and the mirror axis, and in your case would correspond to looking 90° left. I haven't fully worked out the raytrace algorithm for off-plane viewing to see if the focal surface still lines up. The math is not undoable, I just haven't taken the time to do it yet.

As things are going, I think we may not be too far from having a functional prototype mirror, which should at the very least give us a good idea of the feasability of this project. If you can wait a few more weeks before cutting parts, I think we'll have a lot more to report.

Oh, and your wife must be very understanding to go along with having your simulator take up so much of the bedroom.

mikesblack

10-28-2010, 08:05 PM

Thanks for pointing out this document. I understand the meaning of offset. I did re measure this point and rather than 18 inches as I had written, I think I am closer to the 21 inches as per the real aircraft.

If you could explain, I am not totally sure I understand this?

"My cockpit will be single-seat, and the only horizontal offset I'm allowing is to account for my eyes being forward of my neck. In that case, the optics are consistent throughout the horizontal field of view. In a two-seat cockpit, these optics calculations only hold true along a plane defined by the eyepoint and the mirror axis, and in your case would correspond to looking 90° left."

wledzian

10-28-2010, 09:08 PM

I am not totally sure I understand this?

Me neither.

The raytracings I've done to determine the screen shape are for rays in-plane with the mirror axis. A ray in this plane stays in this plane from the screen to the eyepoint, so my calculations are relatively simple. I cast a ray to the mirror, determine its intersection point and angle, and calculate the reflected ray. Doing this with several parallel rays produces an intersection point which defines a point on the screen. It doesn't matter that the eyepoint is offset from the axis, as the rays are still in-plane. Since I'm not worried about a second crewmember, this works well for me. A small offset to allow for my eyes being forward of my neck (the rotational axis of my head, assumed to be coincident with the center of the mirror) has no effect on the raytrace calculations.

For more significant offset, it cannot be assumed that the cast rays will be in plane with the mirror axis. I now have to cast the rays in a plane defined by the mirror center (not the axis) and the ray itself. This requires transforming the coordinate system to the new plane, casting the rays, determining the intersect, re-transforming the screen point to the original coordinate system, and finding a clean way to visualize the new screen points in relation to the in-plane surface.

Visualize if you will, the mirror around your cockpit. If the center of the mirror is directly between captain and copilot and you look directly to your left (as captain), you'd expect to be looking at a reflection of some point on the screen directly above your line of sight. On the other hand, if you look directly forward, you'd expect to see what is directly in front of the aircraft. This image, if properly located on the screen, will be directly over the cockpit centerline. Your line of sight is directly forward to the mirror, but the reflected ray is up and to the right, to intersect with the centerline of the screen.

The problem is that the collimation is not perfect. The directly-forward eyelines for the captain meet the screen slightly to the left of forward, and for the copilot, slightly to the right of forward. The offset is significantly less than if you were looking at a real image on a surface a few feet away, but it is real. The effect is lessened by the use of larger mirrors.

I haven't done the math yet, so beyond the concept I don't have an idea about the magnitude of the distortion or whether it will be acceptable or absolutely horrible. Once we have a working prototype, we'll be able to tell you more.

mikesblack

10-28-2010, 11:57 PM

Thanks. Have to say that I'm very impressed by your level of understanding and detailed knowledge of this subject.

There is definitely quite a bit to it, and for me, without the good fortune of this site and more specifically folks like you who have been most generous with sharing knowledge, I would be lost and without hope of even being close to getting this done.

I am looking forward to the process, and even if not successful, I still think learning this has been worth the effort.

Cheers!

castle

10-29-2010, 01:08 AM

Your wife has to be one fine lady!

4405

Bit fortunate here, have an extra stall in the garage, but it is a bit tight. Starting to build the shell and already seeing that it is not going to work if and when the mirror system is installed.

4406

I jokingly suggested pehaps the wife would like to park her car outside and along with an icy stare she suggested maybe I wouldn't mind sleeping in my truck. ;-)

All kidding aside, gotta love them, amazing how they tolerate the kid in us and all our crazy hobbies

mikesblack

10-29-2010, 01:46 AM

She says she loves me for that quality, of course that's until I start really start acting like a kid or perhaps I should say childish. Then she gets annoyed.

castle

10-30-2010, 12:34 PM

While I've gotten some prelim numbers that suggest you might be able to fabricate three acrylic forms for around $2K (does not include first surface mirroring) and wanted to use those on a vacuum system instead you would have to drill a gazillion tiny holes to suck up and stretch the mylar. So here is a crazy idea..

Going back to the idea of building a more conventional frame; use a multilayer approach for the concave surface. Base layer is strips of conventional peg board, cover that with a coarse cloth, apply a top layer of felt. Use two sided carpeting type in horizontal and vertical strips to hold the sandwich together and bonded to the board surface.

JW

crashdog

10-30-2010, 02:43 PM

Don't know if this vid has been shown before it's one year old. But I just stumbled upon it. You can see the mounting of the collimated visual from day 9 to day 11. Enjoy :)

http://www.youtube.com/watch?v=Wqq4-XC5f8U&feature=related

Gery

mikesblack

10-30-2010, 03:39 PM

crashdog,

That was great. Thanks for bringing this up. I have been looking for something like this.

Fantastic,
Mike

Matt Olieman

10-30-2010, 03:56 PM

Gery, FRIGGEN FANTASTIC!!!!!!

I haven't seen this one, good find and THANKS!!!!! :) :) :) :)

Matt Olieman

wledzian

10-31-2010, 10:58 PM

Gery -
That's awesome! Day 10 is exactly what I've wanted to see - very helpful!

marito

11-03-2010, 11:36 PM

Hi guys

My first post here,and just come to bring some hope for all of homebuilders..
Im from Argentina,and not able to find mylar here,so I do my test about collimating mirror with mirror film for window's cars,an air compressor and fiberglass resin,and i get good results,here are some pictures...sorry,don't know how to put thumbs here :-?

http://img27.imageshack.us/img27/3106/p8293929.jpg

http://img189.imageshack.us/img189/61/p8293930.jpg

http://img600.imageshack.us/img600/7712/p8293942.jpg

http://img97.imageshack.us/img97/4084/p8293950.jpg

http://img339.imageshack.us/img339/6541/p8293954.jpg

http://img834.imageshack.us/img834/6262/p8303980.jpg

http://img109.imageshack.us/img109/3470/p8303986.jpg

http://img708.imageshack.us/img708/2085/p8303987.jpg

http://img5.imageshack.us/img5/2936/p8303989.jpg

wledzian

11-07-2010, 03:48 PM

Progress on Saturday -

Gleaning a bit from the CAE video, we built up some ears for the prototype 60° mirror frame. We still need to build extensions for the top and bottom edges to act as gluing surfaces and install a vertical brace or two, but as the hour was late and all were tired, that will have to wait until next week. Once that is complete, we should be able to mount the mylar for a test run.

http://www.mycockpit.org/photopost/data/536/IMG_3599_small.jpg

Matt Olieman

11-07-2010, 04:16 PM

Thanks for the pic, it put's a smile on my face. WOW, nice work and wish you all the luck and I wish I was there with you. I want it to work!!!!!!!

Matt Olieman

wledzian

11-21-2010, 02:29 AM

Update Saturday 11-20-2010, 10:30 PM:

IT WORKS!

(details to follow later...we're having too much fun actually USING it!)

geneb

11-21-2010, 04:42 AM

Why yes. Yes it does. :D

http://www.youtube.com/watch?v=8yaDnXYlf8k

Couple of things to note - the screen we're using is made of paper. Imagine your average guy wrapping a christmas present - a BASKETBALL shaped present. Yeah, it's got LOTS of wrinkles, but for a proof of concept screen, it does the job handily.

I suspect Wayne & I will write more about this in the upcoming week, but it's 12:41am and we're tired. *laughs*

Thanks all!

g.

crashdog

11-21-2010, 04:50 AM

Fantastic proof of consept ! Looks already really cool !

geneb

11-21-2010, 12:14 PM

More video - with extra cheesy narration included free!
http://www.youtube.com/watch?v=ywEtU7VnzPc
http://www.youtube.com/watch?v=2lZLTY021VQ

The setup under vacuum:

http://www.diy-cockpits.org/coll/images/mirror_drawn_down.jpg

wledzian and I are still in shock. :) (You have _no_ idea how undignified it sounds when two grown men giggle like school girls)

g.

Matt Olieman

11-21-2010, 12:37 PM

WOW!!!!!!!!!!! CONGRATULATIONS, what a feat!!!! THIS IS THE MOST AMAZING FEAT IN OUR HOBBY!!!!!!!

This is a major break through!!! You've changed our hobby to the ultimate level!!!

You guys have just made history!!!!!

I LOVE IT!!!!

Matt Olieman

Joe Cygan

11-21-2010, 01:39 PM

Yes, this is very good to see. It certainly keeps the "spirit" up in the home builder scene. This is obviously not new technology by any stretch of the imagination, but it is nice to see it finally show up in this regard.

geneb

11-21-2010, 02:14 PM

Thanks guys. While not "new" technology, it's not exactly simple either. :) Your average jigsaw jockey is not going to build one of these any time soon. The parts that make up the framework have to be very, very, very accurately cut.

Now if you guys think THAT was cool, wait till you see what we do next. :DDD

g.

Matt Olieman

11-21-2010, 02:26 PM

Gery, looking forward toward "NEXT" :)

Matt Olieman

wledzian

11-21-2010, 02:32 PM

First application of vacuum. We weren't sure what was going to happen; we were all pleasantly surprised.
http://www.youtube.com/watch?v=y67TAo9Lv5g

Display in use. Notice that as the camera is moved, the image stays still, WAY off in the distance.
http://www.youtube.com/watch?v=qJkZTvMfZac

geneb

11-21-2010, 02:46 PM

*raises hand* Who's Gery? *laughs*

BTW, when all the leaks were sealed, the mirror did properly form a spherical section! I used a Fein Turbo III dust collector for the vacuum source.

g.

Mike.Powell

11-21-2010, 02:47 PM

Congratulations, guys. Fantastic work.

geneb

11-21-2010, 02:54 PM

Thanks Mike! You provided very valuable insight and inspiration to us!

g.

Joe Cygan

11-21-2010, 03:52 PM

Now if you guys think THAT was cool, wait till you see what we do next. :DDD

g.

Can hardly wait. Should be very interesting.

Joe

Hessel Oosten

11-21-2010, 05:43 PM

OOOOOOOHHHHHH !

(that's Dutch for OOOOOOOHHHHHH !)

Great guy's ! Thanks !

Hessel Oosten

Jordan Farmer

11-21-2010, 06:48 PM

What a massive breakthrough guys! Hopefully, it shouldnt be too long until these start cropping up all over the place! I still dont understand how it works, but at least it does! Great work,, and im looking forward to seeing more about it!

Oh, one more thing, i think you are the most envy'ed guys in the simming community now :p

Jordan

ivar hestnes

11-21-2010, 09:07 PM

Very impressive work guys!!
I am sure you have spent huge amounts of time to figure it out. Looks very promising so far. keep up the good work:)
Love the videos!!

Neil Hewitt

11-21-2010, 10:35 PM

Fantastic achievement, guys! Presumably with a powerful enough vacuum source this could scale up to a full-sized wraparound for a 737-sized sim - I guess you'd do it in segments with a separate vacuum source in each? Although I guess you've got to find some way to mask the noise long term ;)

You could build these and sell them for serious money - I'm sure there's plenty of folks here who'd be willing to fork out a small fortune for the ultimate display.

Just wow.

NH

wledzian

11-22-2010, 12:28 AM

Fantastic achievement, guys! Presumably with a powerful enough vacuum source this could scale up to a full-sized wraparound for a 737-sized sim -
It doesn't take a tremendous vacuum to draw down the curve. The major limits to size are:

Amount of stretch required. To go beyond about 40° vertical field of view, more than 2% stretch is required, which runs dangerously close to Mylar's yield strain point. Do that, and the mirror goes *pop*.
Width of available Mylar sheet. Since the flat-pattern of an unformed mirror is a flattened conic surface, increasing the horizontal field of view increases the vertical width of the mylar sheet. To go big, you need a really wide piece of Mylar.

I guess you'd do it in segments with a separate vacuum source in each?
We had originally considered segments as an easy way to go wider, but upon seeing the degree of distortion at the edges, this is pretty much a non-option. If you look carefully at the photo in post#128, you'll notice a line of distortion running vertically where the 'ear' meets the center section. In this case, the mirror is barely touching the underlying structure, and is being distorted by less than 0.01" judging by the known depth of the imperfections in that part of the frame (that piece of structure just happens to be faceted). That distortion disappears when the pressure is backed down a little bit, but it would be extremely difficult to build a segmented mirror without very distracting distortion at the edges.

Although I guess you've got to find some way to mask the noise long term ;)
That's probably not a huge issue - my plan is to build my sim in my office and keep my shop-vac in the garage, with a small vacuum line running through the wall. I'm confident that anyone determined enough to do this would find a way to get the vacuum out of the room.

You could build these and sell them for serious money - I'm sure there's plenty of folks here who'd be willing to fork out a small fortune for the ultimate display.
Unfortunately, that's NOT going to happen. Many of the techniques required to build this mirror are covered by active patents. To build this for ourselves for the purposes of recreational use or satisfaction of curiosity (to see how it really works) is generally OK, but we'd be opening ourselves up to some serious legal trouble if we tried to make a business of it.

Just wow.
We had the same thought. And believe me when I say that the photos and videos do NOT do it justice. When the mirror hits the right curvature, the image just jumps out into the distance - your eyes instantly relax, and everything just looks so real. It's freaky.

benjaminransom

11-22-2010, 12:42 AM

glad to know it....it always be having nice with display systems.....

mikesblack

11-22-2010, 04:11 AM

:pCongratulations! Must bee a hopeful moment. It has been fun watching this concept evolve to a real model. Keep the pictures and commentary flowing. I look forward with to start experimenting with great inspiration. Thank for that guys.

jackwall

11-22-2010, 07:30 AM

Way to go fellas .... trail blazing stuff. These first 'fire it up, let's see what it does' moments are the elixer of innovation and motivation. To echo Jordan above, alot of positive envy I'm sure going around.

jack

Matt Olieman

11-22-2010, 08:06 AM

I went to bed and woke up this morning thinking about Gene and Wayne's accomplishment and what it means to our hobby. I'm so excited about this and YES I believe in the near future this will be a common device within our community of Flightsim builders. :) :) :)

I can't begin to tell the countless hours I've spent over a 15 years trying to accomplish the same thing, of course most of that time I didn't know what Mylar was. It's thanks to internet and people like Mike Powell who presents us with all sorts of technical information and points us to the right direction, that helps make this possible.

This topic has been discussed, as far back as I can remember, where there was a forum to discuss flightsim building in (that's beginning of time) :) The same questions and same outcome every time. I thought the same thing, as every time when this topic started, here we go again. BUT with Gene and Wayne's determination, they made it work, truly AMAZING.

I realize this is not a new technology, but in our eyes, as builders, it was an impossible technology and cost prohibiting feat for our builders, Gene and Wayne proved that wrong. :) :) :)

Thank you again Gene and Wayne and Mike Powell for providing such pertinent technical information.

WOW!!!!

Matt Olieman

vybhav

11-22-2010, 11:11 AM

Well summed up Matt, couldnt agree with you more.

Regards

geneb

11-22-2010, 08:13 PM

Here's a walk-around video I did a little while ago.

http://www.youtube.com/watch?v=zogFny49zrI

Enjoy!

g.

AK Mongo

11-22-2010, 08:31 PM

That video really helped those of us who had never thought twice about a collimating display to understand how one works. How are you going to cover the display? Mylar again?

geneb

11-22-2010, 08:43 PM

That video really helped those of us who had never thought twice about a collimating display to understand how one works. How are you going to cover the display? Mylar again?

I'm not quite sure what you're asking. Are you refering to enclosing the mirror?

g.

AK Mongo

11-22-2010, 08:50 PM

Probably used the wrong terminology, but I meant the part you have covered with paper.

Joe Cygan

11-22-2010, 09:09 PM

Here's a walk-around video I did a little while ago.

http://www.youtube.com/watch?v=zogFny49zrI

Enjoy!

Great job Gene! Looking forward to future updates.
Joe
g.

Great job Gene! Looking forward to future updates.
Joe

geneb

11-22-2010, 10:33 PM

Probably used the wrong terminology, but I meant the part you have covered with paper.

@AK Mongo - The full sized screen will be 180 degrees wide (the test screen is 60 degrees wide). The spaces between the ribs will be filled with foam and then hot-wire cut to shape. It'll then be smoothed out with bondo. At that point we'll either skin it with a high-contrast commercial screen material, or we'll shoot it with the type of Glidden paint that Mike mentions in the display chapter of BRFS.

@Everyone: Thanks for all the kind words! This has been an incredible project - and I'm really looking forward to the next steps. The only sad thing is that I won't be able to use it on the F-15. Collimated displays and bubble canopies don't get along well. :)

(but it's a GREAT excuse to build Ricardo's Embraer-like cockpit if it'll fit within the screen radius. :D )

g.

geneb

11-22-2010, 11:24 PM

For those that are interested, here's what the rear-projection screen for a 737 FFS looks like:

http://www.diy-cockpits.org/coll/images/rearprojectionscreen.pdf

g.

yoss

11-23-2010, 10:54 AM

For those that are interested, here's what the rear-projection screen for a 737 FFS looks like:

http://www.diy-cockpits.org/coll/images/rearprojectionscreen.pdf

g.

Lol , i remeber this item was for sale some two years ago for 500 euro or so...
Of course , local pickup had to be arranged ....

choffmann

11-23-2010, 04:27 PM

geneb

11-23-2010, 04:41 PM

I must admit I haven´t read this whole thread, and maybe I am a little dim, but what I´m not sure about yet is:
With a 180 degrees screen, how do you set up your projector(s)? You would obviously need more than one, probably three. I ask this with special attention to the focus issues, that Mike pointed out in his tips "depth of field". What I mean is, the projector setup in your system to me seems much more tricky than in a direct beam system, like the one e.g. Ivar Hestnes uses.
Any hints?

Chris

Oh, and BTW: thanks very very very much for your work!

Chris, the 180 degree version will indeed use three projectors. There will be some slight focus issues for sure, but I don't anticipate that they'll be that bad. Keep in mind that to get it "perfect", you've got to spend some serious coin on optical correction.

I don't know about Wayne, but I really didn't notice any focus issues at all with the test rig. The extremely low resolution could be a contributing factor as well. The projector being used has a native resolution of 800x600 and it was interpolating an 1024x768 input signal. We'll have to see how it looks when tried with an HD projector, but I don't anticipate any insurmountable issues.

g.

Matt Olieman

11-23-2010, 05:18 PM

Regarding three projectors, or may be more? Early versions of the collimated display systems had up to 5 projectors, these were CRT's (three tubes) to keep things in focus and get a higher resolution. The projectors were mounted on the outside of the sim (keep the heat out) and a small portion of the front of the projector was inside the rear display unit. Although the 5 projector sim I flew, when you looked around the edges, the edges were out of focus.

With today's technology, projectors have more of a depth of field ration then earlier models, also the resolution has increased dramatically. Let's not forget about the size of the units. My first projector, NEC 1200D (I think), it took two people to pick it up.

There are Level D's with 180+ degree using 3 projectors today.

Matt Olieman

wledzian

11-23-2010, 05:28 PM

I didn't notice any focus issues either, and I was specifically looking for them. In particular, there was a bit of a screen-door effect due to the small gaps between pixels. I expected that if there were significant issues due to a shallow depth of field, there would have been enough blurring to make the screen-door difficult to see at either the edges or middle of the screen. I noticed no such issues, so the defocus was significantly less than a single pixel.

As gene said, we'll most likely be using three projectors. 3 HD projectors would be ideal, but I don't think that is supported by TH2Go or by DirectX (4096-pixel max horizontal resolution - correct me if I'm wrong). Two HD projectors may get the job done, if there's enough depth of field to front-project onto a 100-degree section of the screen.

geneb

11-23-2010, 05:39 PM

There are folks using the Digital version of the TH2G running horizontal resolutions higher than that - think three 1900x1200 displays. It may be more effective to just add two more GTX260 video cards to the system - there's certainly enough CPU in there and the power supply is 1KW.

g.

Matt Olieman

11-23-2010, 05:52 PM

I would think 2 projectors would be stretching it, BUT, who knows, you guys just worked out a miracle. LOL :)

Matt Olieman

Joe Cygan

11-23-2010, 06:11 PM

This picture might make it a little clearer on how the collimated screen works for multi projectors. I have been working on this subject with my wife for a very long time and I will try to contribute to this thread.
http://i56.tinypic.com/331hveu.jpg

Joe

brianwilliamson

11-23-2010, 08:23 PM

Great news and a big congratulations for all the great work and success you have achieved. I am very interested in anything to do with improving visuals, as I have just re-arranged the Airbus and the 3 projectors with a little better resolution and FOV. I am now using 180 degrees on nthe Triplehead with FSX. I have had to back off quite a bit on the graphics as one would expect, using that sort of screen size (3x1280x720), but it is working very well. Can even use YMML from Orbx, but need to taxi at a reasonable pace !!

Keep up the great work...............Brian W.

Bernie

11-23-2010, 11:45 PM

Hi,

This is a wonderful step in the developement of the perfect home simulator. Now don't shoot me down in flames here, but while the Milar is in the stretched form, is it possible to spray the rear surface with some type of product (Who Knows What) to make the shape permanent. Is there anyway this could be layed on it's back and filled with a product such as foam to form a permanent mould to which could be sprayed with a refective product (Who Know What). These are just thoughts buzzing through my head and feel, as silly as they sound, there might just be something that is useful for further progress.

Kind Regards

Bernie.

Mike.Powell

11-24-2010, 12:16 AM

Bernie

11-24-2010, 12:22 AM

Actually, yes.

US patent #3,549,803 describes making a curved mirror by coating the back of a Mylar mirror with multiple layers of urethane foam and fiber glass.
Hi Mike,

Does this mean that it can't be done by a hobbyist?

Kind Regards

Bernie.

Mike.Powell

11-24-2010, 01:19 AM

That particular patent was issued December, 1970. I'd be surprised if it were still in force. You can check it out at http://www.google.com/patents/about?id=Z2ViAAAAEBAJ&dq=3,549,803

geneb

11-24-2010, 12:53 PM

The trick is, how do you apply the foam & fiberglass while the mirror is under vacuum? :)

g.

Jordan Farmer

11-24-2010, 01:05 PM

Well, this has been onmy mind too. All i could come up with is to make a negative mould. then you could create as many mirrors as you want. So, you turn on the vaccum, then apply whatever you want to the outside, and then, when you take this shape away, you will have a master mould, and you can then make the mirror from that. Its the same process as making resin moulds from silicon, only on a much larger scale!

Let me know what you think

Jordan

Mike.Powell

11-24-2010, 01:17 PM

The trick is, how do you apply the foam & fiberglass while the mirror is under vacuum? :)

g.

The trick is that you don't. You flip things over so you can pressurize the Mylar from the reflective side. It means building a totally different frame for holding the Mylar.

Matt Olieman

11-24-2010, 01:20 PM

http://mycockpit.org/images/collomating-mirror/NASA%20rfd7.jpg

This is a 180 degree system (a very old one). This system has 4 projectors and the projectors are out of the sim or rear display compartment. Projecting at a angle downwards. The 5 projector system I mentioned earlier was similar to this one, except it was level D.

Matt Olieman

rjvcarvalho

11-24-2010, 01:20 PM

How curved glass is made:

http://www.youtube.com/watch?v=1tcXCfDzCjY

geneb

11-24-2010, 01:45 PM

@Jordan - any mold has to have a surface that is mirror-perfect. That's, really, really hard to do.
Commercial flight simulators use thin film mirrors because they're very light and compared to the same size in glass, dirt cheap to make.

@Matt - was that sim built that way or was it on a motion base at one time? I've never seen a static sim with a collimated display and no base. It's weird. :)

@Mike - Smart aleck. :D

g.

Matt Olieman

11-24-2010, 02:16 PM

@Matt - was that sim built that way or was it on a motion base at one time? I've never seen a static sim with a collimated display and no base. It's weird. :)

g.

I don't recall this particular one.... :(

I used to travel quite a bit (cross country), I'd try to hit every Flight Sim School there was. I do remember seeing static sims with a collimated display.

Matt Olieman

makoy

11-24-2010, 05:47 PM

What about if not sucking air out from backside of mylar, but pushing air in front side.
I think it will make same thing to mylar and you can add something urethane foam etc to backside.

wledzian

11-24-2010, 07:06 PM

What about if not sucking air out from backside of mylar, but pushing air in front side.
I think it will make same thing to mylar and you can add something urethane foam etc to backside.

I believe the patent Mike Powell mentioned specifically states that the first layer should be some sort of uniform material (a few coats of plasticized primer should do), as the voids in foam result in an imperfect surface. Otherwise, you've got the idea.

Bernie

11-24-2010, 07:51 PM

What about applying the material to the rear surface while not being stretched and then using the stretching process to pull it into shape giving the first layer time to set.

Kind Regards

Bernie.

Mike.Powell

11-24-2010, 08:11 PM

What about applying the material to the rear surface while not being stretched and then using the stretching process to pull it into shape giving the first layer time to set.

Kind Regards

Bernie.

Mylar takes a lot of force to get it into the proper shape. I doubt a single layer on the back would hold the proper mirror shape. I think you would need to apply multiple layers and let them all cure and gain strength if the finished mirror is to be useful.

SU-Medo

11-25-2010, 07:51 AM

Hi Guys ..

Congratulations , this is a historical moment in our hobby !! cheers :D

you made a great step guys , who believed it's possible to make a DIY collimated mirror display system for our replicas !! , So we can modify & discover ways to solve the distortions in the view that appeared in the videos ..

I'm so sorry my english isn't well btw it was so tiring to translate words in your last 169 posts :| .. I have read all posts as i can & I have already got the general idea ... I'm trying to make a frame from wood with a vertically - horizontally FOV 40 - 180 degrees , & I'm going today to a mirror factory to ask them if they can made a mirror that can be formed on the wooden frame form .. but in all your posts you were talking about "Mylar" and you didn't talk about making the mirror at a factory or a workshop .. whatever .. is it expensive to order a mirror by the shape we want ?? or they can't do it in an accurate optical properties ??

another question .. how the vacuum form the mylar ?? please explain because i didn't get how it form the shape of it ..

Thanks for your nice thoughts & posts ..

Matt Olieman

11-25-2010, 08:37 AM

SU-Medo

11-25-2010, 12:32 PM

Did you look at all the videos? Gives you a good idea how this is done and the genius of it all. :) :) :) It's not as simple as to ask a mirror company to build this, there's a bit more to it than just that.

Most of your questions will be answered in this thread. It's quite informative.

Matt Olieman

Thank you Matt for your post ..

I watched all the videos , but I didn't understand how the vacuum form the Mylar on the frame !!!
but i noticed that the rear-projection screen isn't uniform & a bit distorted .. is this the reason why the picture on the mylar isn't uniform ?? or the reason is that the mylar itself ??

I went to the factory , they can do it .. but the cost made me Deaf !!

Plz tell me the theory of using a vacuum .. ( what it do )

Thanks

Matt Olieman

11-25-2010, 12:37 PM

Thank you Matt for your post ..

I watched all the videos , but I didn't understand how the vacuum form the Mylar on the frame !!!
but i noticed that the rear-projection screen isn't uniform & a bit distorted .. is this the reason why the picture on the mylar isn't uniform ?? or the reason is that the mylar itself ??

I went to the factory , they can do it .. but the cost made me Deaf !!

Plz tell me the theory of using a vacuum .. ( what it do )

Thanks

@ SU-Medo, The questions you are asking are all answered in this thread. I understand the difficulty with the language barrier, but it's here. Please try to translate using Google translator, perhaps that will help.

Also read Mike Powell's articles related to collimated displays: HERE (http://www.mycockpit.org/forums/content.php/151)

Matt Olieman

geneb

11-25-2010, 12:57 PM

Quick summary - The frame forms the outline of a a spherical section and when the mylar is properly placed on the frame and you apply a vacuum source to it, it pulls the mylar into the spherical section shape that the framework "describes".

This is what it looks like as a "solid":
http://www.diy-cockpits.org/coll/images/60h40v_model.jpg

As soon as you turn off the vacuum, the mylar "relaxes" and no longer forms the mirror. This is shown especially well in the first video that Wayne posted that shows the first time we applied vacuum to the mirror.

Also, we're not using rear-projection. :)

The majority of the weirdness you see in the videos is the result of the kraft-paper wrapped screen. It will get MUCH better when skinned with material that's not doing its level best to fold, crease, wrinkle and tear itself while being wrapped around the screen framework. :)

g.

SU-Medo

11-26-2010, 12:57 AM

Matt .. thank you for Mike Powell's articles , I appreciate that for you .. :):)

Quick summary ..... The majority of the weirdness you see in the videos is the result of the kraft-paper wrapped screen. It will get MUCH better when skinned with material that's not doing its level best to fold, crease, wrinkle and tear itself while being wrapped around the screen framework. :)

Thank you so much for the summary , I got it now .. :)

Whatever the type of projection ( rear or forward ) , I saw a big ball from white acrylic in a shop , It's used for containing a lamp for lighting in streets .. It was big enough ( by guessing it has a radius about 3' feet ) , I think we can cut a part similar to the curvature of the Mylar mirror's frame to use it as a rear/forward-Projection screen .....

Matt Olieman

11-26-2010, 09:41 AM

castle

11-26-2010, 05:46 PM

I wondered about using something like SU-Medo mentioned (the acrylic white ball).

Rear projection would still be a preference, well, for me, anyway..... :)

I've played around with sheets of Lexan, forming shapes. Lexan is easy to form and takes a little heat, it's also easy to repair when scratched. Anyway, I thought about this when I saw the forming of glass video, with lexan it's the same method, but less heat.

Matt Olieman

Here is some info on paints for front projection systems you all might find useful for the collimated projection screen or any DIY front projection system for that matter

http://myplace.frontier.com/~vzepdzse/behr_paint_test%20screen.htm

I'll be using it on my 180 wrap around, not collimated but okay for now. Playing with mirrors geometries to shorten throw distances, idea is to bend a surface into shape with something like Lexan then skin it with a one mil mylar sheet to create a FS mirror. The amount of bending is amazingly little in the vertical, radius of curvature on the order of 15 to 17 feet Haven't tried it yet, but with a conventional mylar mirror was able to cold bend it to produce the following mesh pattern shown,, this is with a VERY rough first order mesh distortion program which will be fine tuned and enhanced to handle localized warping as needed and edge blending

JW

Bernie

11-26-2010, 06:33 PM

Here is some info on paints for front projection systems you all might find useful for the collimated projection screen or any DIY front projection system for that matter

http://myplace.frontier.com/~vzepdzse/behr_paint_test%20screen.htm

I'll be using it on my 180 wrap around, not collimated but okay for now. Playing with mirrors geometries to shorten throw distances, idea is to bend a surface into shape with something like Lexan then skin it with a one mil mylar sheet to create a FS mirror. The amount of bending is amazingly little in the vertical, radius of curvature on the order of 15 to 17 feet Haven't tried it yet, but with a conventional mylar mirror was able to cold bend it to produce the following mesh pattern shown,, this is with a VERY rough first order mesh distortion program which will be fine tuned and enhanced to handle localized warping as needed and edge blending

JW

Hi,

Here is a link to the use of a curved Sintra sheet and a mirror. The information may be of interest to you if you haven't already seen it.
http://www.biagettis.com/737simproject/737simproject_008.htm
Kind Regards

Bernie.

Mike.Powell

11-26-2010, 07:22 PM

....I'll be using it on my 180 wrap around, not collimated but okay for now. Playing with mirrors geometries to shorten throw distances, idea is to bend a surface into shape with something like Lexan then skin it with a one mil mylar sheet to create a FS mirror. The amount of bending is amazingly little in the vertical, radius of curvature on the order of 15 to 17 feet Haven't tried it yet, but with a conventional mylar mirror was able to cold bend it to produce the following mesh pattern shown,, this is with a VERY rough first order mesh distortion program which will be fine tuned and enhanced to handle localized warping as needed and edge blending

JW

Nice work!

castle

11-26-2010, 08:31 PM

Hi,

Here is a link to the use of a curved Sintra sheet and a mirror. The information may be of interest to you if you haven't already seen it.
http://www.biagettis.com/737simproject/737simproject_008.htm
Kind Regards

Bernie.

Yes, I saw that. Thank you.

Two aspects of that approach I'm trying to improve on. First, using a curved mirror and screen rather than a flat acrylic provides 180 degree with a screen radius of six feet (~2M) This allows you to increase the FOV in the vertical; important for the side view where the side windows are closer plus by placing the mirrors at the edge of the cabin, you reduce or eliminate the problem where the cabin edge might shadow the reflected image, second FS mirrors to eliminate image ghosting can be expensive in larger sizes and customized curved ones can be very expensive. You can create a FS mirror from a conventional mirror by removing the protective backing. It can be done with some care, but that will be a flat surface.

If using a thin mylar skin stretched on a concave surface works, it opens the door for an effective DIY low cost solution and also one to customize a mirror shape. And then create the appropriate distortion mesh designed for the precise arrangement of cameras, mirrors, and screens.

Cheers
JW

geneb

11-27-2010, 12:28 AM

Wayne stopped by for a bit today and we were able to get some "pre-saturday" work done. :D

These parts....
http://www.diy-cockpits.org/coll/images/screen_frame_parts.jpg

Will combine to build this...
http://www.diy-cockpits.org/coll/images/screen_assembly.jpg

The rendering above is the 225 degree screen for the new mirror. The spaces between the ribs will be filled with 2" insulation foam that's been hot-wire cut to shape. The framework is made from 7/16" plywood and the thin ribs are to be cut from 1/8" hardboard. Not shown in the drawing is the supporting structure that will be on the top & bottom of the screen.

It turns out that my original screen design will work out with 56" wide mylar, so the new mirror will cover a vertical FOV of 40 degrees and right around 220 degrees or so horizontally. The diameter remains the same at 8 feet.

The screen as designed is about 52" or so across at the widest point of the base ring. It's a bit wider than that overall because of the ribs - but not large enough to properly do rear projection using a vacu-formed screen.

More tomorrow!

g.

geneb

11-29-2010, 12:03 PM

Here's a link that shows what we got done this past Saturday:

http://www.diy-cockpits.org/coll/collimated_display_page2.html

Hopefully the server won't fall over again today. (motherboard is fading I think)

It turns out the only active patent we have to worry about covers the "ears" that help form the mirror. I don't know that there is a practical way around that one, but we'll look into it further at some point.

g.

Mike.Powell

11-29-2010, 12:50 PM

Thanks for the link and pix, Gene. GREAT work!

geneb

11-29-2010, 01:19 PM

Thanks Mike. I've been looking into 1200x800 projectors and boy... ka-ching! :(

g.

Matt Olieman

11-29-2010, 01:34 PM

Yes Gene, thanks for the pics. :) I tried to look for more, but you've got them well hidden :p

Projectors.... I don't know which ones your looking at, but they've come done quite a bit from a few years ago. Yes, I know, still a bunch. I thought they would be coming down quit a bit more by now. :(

I'm amazed at your workmanship..... WOW, you've got the touch!!!! I can't wait for more pics.

Matt Olieman

rjvcarvalho

11-29-2010, 02:11 PM

geneb

11-29-2010, 02:12 PM

Thanks Matt. I'm looking at the Epson EX7200 right now. They can be had as low as $650, but it's still painful, specially if I need to throw in a new TH2G as well. If it turns out two more GTX260 video cards are cheaper than one TH2G.... :)

I'm going to start the design work on the 225 degree mirror framework this evening. I'm going to be puzzle-piece'ing quit a bit of it. The design needs to be both portable and easily to assemble on-site at Wayne's house. It won't be nearly as deep as the 60 degree frame though. I'm going to design it so that the base is between 2 and 4 inches deeper than the spherical arc in order to keep it as small as possible. The back will be round instead of squared off like it is and there will be a couple of different vac points as well as a panel that I can access the interior with. I'm going to be experimenting with controlling the vacuum by Arduino and a barometric pressure sensor (did I mention this already?!). I'm also going to try a much smaller vacuum pump that has a very small CFM rating (cubic feet per minute) flow, but can draw down a higher vacuum. The Arduino would control the power to the pump via relay as well as a solenoid driven vacuum valve.

g.

Joe Cygan

11-29-2010, 02:59 PM

castle

11-29-2010, 03:13 PM

Fry's had a sale on two months ago on some Viewsonics PJ-551Ds for $495.

Resolution is 1280x1024, so I picked up two. Should check, but think that is native res and thery are DLPs, still in the boxes. Once I get the mounts and mirrors up and the mesh software working will fire them up. Maybe before Christmas..

Not fair you have all those neat tools like a CNC and cutting table to work with ;-). I'm stuck with a table and band saw and a drill press..

Marvelous work, Gene

JW

geneb

11-29-2010, 04:28 PM

Castle, the native resolution of that projector is 1024x768. It make take a high resolution input signal, but it'll scale it down to fit. You'll get the highest image quality if you feed it at its native resolution.

Here's the stats from the Projector Calculator:
http://www.projectorcentral.com/ViewSonic-PJ551D-projection-calculator-pro.htm

The screen was Wayne's trial by fire with AutoCAD. He did good. :D

g.

geneb

11-30-2010, 12:18 AM

Just a quick update - this is what the mirror "solid" looks like;
http://www.diy-cockpits.org/coll/images/mirror_frame_solid.jpg

This will be cut apart into the bits needed to make it into a framework. The top is 4" wide and the gap is about 68" wide. The mirror frame covers 225 degrees.

[Update! I screwed up - the arc should only be 190 degrees.]
g.

SU-Medo

11-30-2010, 04:30 AM

Here's a link that shows what we got done this past Saturday:

http://www.diy-cockpits.org/coll/col...lay_page2.html

Hopefully the server won't fall over again today. (motherboard is fading I think)

It turns out the only active patent we have to worry about covers the "ears" that help form the mirror. I don't know that there is a practical way around that one, but we'll look into it further at some point.

WOW Gene , nice work and a great approach ..
I liked the picture of the mirror in the previous link , it's so pure & really can be called a mirror ..
Thank you so much Gene for your work ..

Just a quick update - this is what the mirror "solid" looks like;
http://www.diy-cockpits.org/coll/images/mirror_frame_solid.jpg

This will be cut apart into the bits needed to make it into a framework. The top is 4" wide and the gap is about 68" wide. The mirror frame covers 225 degrees.

g.

I'm working now on a 180 degrees frame , But do you think by your experience that the 225 degrees frame can shape the Mylar easy ?? I think it ll lost its horizontal tension .. Plz correct me if I'm wrong ..

another thing , If we minimized the frame from its down-sides , the Mylar would require a less vacuum power to get shape , because by this way we minimize the total space that the vacuum has to work in ..

http://www14.0zz0.com/thumbs/2010/11/30/08/680130421.jpg

( Sorry for editing your Picture ) ..

geneb

12-01-2010, 08:48 PM

This shows a wireframe of the mirror at it's correct 190 degree layout.
http://www.diy-cockpits.org/coll/images/mirror_frame_wireframe.jpg

g.

HansJansen

12-04-2010, 07:59 AM

I saw this yesterday on discovery, did not know that the projector had a mirror between it and the screen that reflects to the vacum mirror.

http://science.discovery.com/videos/how-its-made-7-flight-simulator.html

I tried to view the video, but after the commercial for a very expensive car which I'm not at all interested in, all I got to see was a message stating "this video is not available in your area"!

(Booh!)

Babeloe

12-04-2010, 11:30 AM

rjvcarvalho

12-04-2010, 01:53 PM

I tried to view the video, but after the commercial for a very expensive car which I'm not at all interested in, all I got to see was a message stating "this video is not available in your area"!

(Booh!)

http://videos.howstuffworks.com/science-channel/40328-how-its-made-flight-simulator-video.htm

As it turns out, there are 2 versions of this video, one with a female voice, the one that is here, and one that i have just watched on tv with a british accented male voice that shows an animation of how the projection works just before the scene where the guy is working on the throttle.

This version here does not have that scene... don't know why.

marito

12-04-2010, 03:12 PM

http://www.youtube.com/watch?v=_1889jWwHUc

SU-Medo

12-06-2010, 04:49 AM

From where I can buy the "Mylar" ( Packaging paper or what ! ) ??? and what are the features that's recommended required ??

Hessel Oosten

12-06-2010, 05:12 AM

Hi (sorry don't know your name),

Search Google for Polyethylene terephtalate
or try: http://en.wikipedia.org/wiki/Polyethylene_terephtalate

It most found on the net in rolls of ~150 cm (or slightly more) width.
Search in the agriculture sector, it's also used in greenhouses to reflect the light (hmm, not necessary in Egypt I presume...).

As you did read before .., it's "coated" with aluminium for the mirror effect.
In Europe about 10 euro per 100 cm (width above).

But before searching too much ...:

Wait for more results of Wayne and Gene.
Without hopefully coming specific information / education (calculation method) it's not doable by trial and error.

Hessel Oosten

Neil Hewitt

12-06-2010, 08:14 AM

http://videos.howstuffworks.com/science-channel/40328-how-its-made-flight-simulator-video.htm

As it turns out, there are 2 versions of this video, one with a female voice, the one that is here, and one that i have just watched on tv with a british accented male voice that shows an animation of how the projection works just before the scene where the guy is working on the throttle.

This version here does not have that scene... don't know why.

"How Stuff Works" (like lots of Discovery programmes) is made with different voiceovers for different regional markets. Quite often the US TV version is not the 'original' voiceover (which can often to be found in the Canadian broadcast instead) because quoted measurements generally need to be converted to Imperial (aka 'English') from metric for US consumption. The UK usually gets a version dubbed with a British speaker and metric units.

So the version you saw was probably the UK version. The US version most likely had a few seconds edited out to fit the slightly shorter US half-hour slot (which has more commercials than you usually get on UK channels).

NH

Neil Hewitt

12-06-2010, 08:24 AM

BTW, if you happen to have access to a VPN service which has an US-based endpoint, you can get around the geo-ip restrictions and watch the video. Not that I would ever condone doing anything so evil and wrong, of course <g>.

NH

Babeloe

12-06-2010, 12:17 PM

How about one of these space blankets? If you don't know them see http://en.wikipedia.org/wiki/Space_blanket.

I don't know if they are actually made of mylar, but they are often called 'mylar blankets'. And they are pretty cheap, and you can get them in a lot of outdoor stores and on the internet.

The downsides I can see is that they are folded very tightly because you need to be able to put it in your First Aid kit, so they will have some pretty sharp folds of witch I don't know if you can get them out with the vacuum or any other way. And it might be a problem with the size, but I think they should be big enough to cover a person's body so a small display should work.

I don't know if it works, but is nearly too cheap to not try this. You can buy these blankets for about 4 euros I think.

Just an Idea

Babeloe

Babeloe

12-06-2010, 02:24 PM

How about one of these 'space blankets' they're made of mylar and pretty cheap. http://en.wikipedia.org/wiki/Space_blanket The only downside i see is that they are folded.

SU-Medo

12-07-2010, 06:26 AM

Hi Hessel ..

It's "Mohammed" you can call me Medo if you like :)

I appreciate for you your reply .. Thank you so much !
The wikipedia link about "Polyethylene terephtalate" that you provided me is so useful , I don't like just following steps without knowledge , I like to understand everything about what i plan to do ..

Thanks Hessel

riche543

12-07-2010, 06:44 AM

ricardos link worked for me here in oz.
Great vid but she makes it sound so simple..lol
Cheers..

Atomic_Sheep

12-10-2010, 11:24 AM

Sorry to butt in with noobish questions but I've got 2:

1.)
Metalized Mylar can be used to make film collimating mirrors. Up to about 40 degrees of vertical field of view, building one is merely difficult. Building one with a 60 degree vertical field of view apparently requires magic. SEOS figured it out a few years ago. Rockwell Collins was so impressed they acquired SEOS in 2008.

What makes 60 degrees so much harder than 40 degrees?

2.) lets talk resolutions or maybe more appropriately aspect ratios? But I haven't really started thinking about the displays of my simulator yet so I don't quite know how to talk about in a way other than layman terms. So, lets take 800x600 resolution and let's take the 40 degree by 60 degree 48" section that geneb has taken for his display. First, how can you display a square image on something that isn't of the same circumference at the top and bottom? Second, the 40 degree (height? wise) and 60 degree (horizontally? wise) gives us a viewing area of approximately 3:2 ratio? The closest one that I see to this would be 16:10 i.e. something like 1280x800 so essentially widescreen? As I said, I don't quite know how displays work so I could be totally wrong in what I'm saying but I hope I've but my question across with enough clarity.

EDIT: Just some additional information, when I tired the SAAB and Airbus simulators, I distinctly remember distortions in the image but they were generally down the bottom and off to the sides. You had to strain/be stand upish to see them so professional displays aren't as perfect as you guys might think (for those who haven't been in the real thing that is). In fact, when you find out the price, you're almost disappointed!

Mike.Powell

12-10-2010, 12:15 PM

geneb

12-10-2010, 12:16 PM

All commercially produced collimated displays have a distortion band around the perimeter edges of the mirror. Those bands are typically masked by physical structure. That's why the only way you'll ever see them is if you move your head to see over/around those masking elements. The only time you'd ever do that is if you're doing it on purpose, which is your own fault at that point. :)

The 60x40 mirror was a proof of concept device. I was using an 800x600 projector because that's all I had available. The full system we're working on now will cover 190 degrees of "intentional" mirror, and out to about 225 when you include the "ears". The video will be provided by three Epson 705HD projectors that run at 1280x800 (and thanks to the kindness of Matt O., I'll be able to run them at that res instead of 1280x768 due to the limitations of the analog TH2G.)

Constructing a 60 degree vertical FOV mirror is mechanically tricky I suspect. Note that the current FAA Level D certification requirement is only 36 degrees. :)

g.

castle

12-10-2010, 01:03 PM

The Mylar initially is a flat sheet and must be stretched into a spherical-section shape. Beyond about 40 degrees vertical arc the stretching exceeds the plastic range of the Mylar. Because its properties change, it's more difficult to make the sheet form a spherical-section surface of a quality suitable needed for the application.

When projecting onto a spherical-section surface there will be geometical distortion. It's compensated for using image warping software like Nthusim.

Agreed, collimated displays are not perfect. The designs tradeoff collimation effectiveness, view box size, distortion, and so on.

Just wondering, can you apply a little "slack" when installing the mylar; you know the radius of the desired shape, compute the arc distance say for 40 degrees at 6 feet requires (40/57.29) * 6.0 = ~4.188 linear feet of mylar in the vertical when the mirrot is formed. The chord distance between the upper and lower frame is something less, but say the mylar is attached with a 4 foot width, will it stretch uniformily to form the mirror, and if that is the case would reducing the amount that the mylar has to stretch allow for a greater vertical FOV.

JW

Mike.Powell

12-10-2010, 01:40 PM

Just wondering, can you apply a little "slack" when installing the mylar; you know the radius of the desired shape, compute the arc distance say for 40 degrees at 6 feet requires (40/57.29) * 6.0 = ~4.188 linear feet of mylar in the vertical when the mirrot is formed. The chord distance between the upper and lower frame is something less, but say the mylar is attached with a 4 foot width, will it stretch uniformily to form the mirror, and if that is the case would reducing the amount that the mylar has to stretch allow for a greater vertical FOV.

JW

I don't know, but I'm inclined to think doing so would introduce unacceptable distortions.

When flat, the Mylar does not have straight sides. The full sheet is actually a broad arc. If slack is added, the edge dimensions must change somehow. Somewhere you'll end up with extra material and wrinkles when fastening the Mylar to the frame.

Build a scale model and experiment with poly drop cloths.

737NUT

12-10-2010, 02:41 PM

Anyone tried Chrome monocote? When heated it becomes drum tight and is fairly strong. Also can be attached to itself to make bigger sheets.

Atomic_Sheep

12-10-2010, 08:38 PM

Hi Geneb, I didn't really pay attention to the resolution of the projector that you were using so I wasn't criticising your setup, I was just trying to figure out what aspect ratios were and how they fit on a spherical display. I just read the wiki page on aspect ratios and my wild stab in the dark in relation to my assumptions as to the relationship between viewing angle and resolutions proved correct or at least I think so. The question that I'm still mulling over in my head though is the whole issue of different circumferences at the top and at the bottom and how an image which is 800 pixels (or 853.3 to be exact) can fit on something that is lets say 100cm up top and 80cm down the bottom or does it simply get scaled due to the ?refraction?/?defraction?

In relation to building a 60 degree vertical field of view. After getting into the topic of cullimated displays just yesterday (just to give you guys an idea of how little I know and how totally not based on any experience my thinking is but)... I was thinking that the only real restriction that I could figure out that made the 60 degree version nearly impossible to make was just the nature of materials and the fact that it would be more difficult to get a nice spherical shape after applying the vacuum as there are essentially 4 points of contact... well... 2 if we're talking about the vertical plane... so in other words, with 40 degrees, it's not very far off the back plate that it needs to vacuum to but with 60 degrees, there's a much bigger space behind it so I was thinking along the following lines:

We know the properties of the Mylar (at least I'm guessing the specfications of the stuff would tell it's elasticity per square cm or inch or meter or whatever... I'm assuming that whoever designed it, knows such properties...). If that's the case, then let's assume the 40 degree version uses a stupid method of calculating the right size material i.e. we take the vertical distance between the two mounting points and the circumferences and then simply attach it, vacuum it and we're done. With the 60 degree version, due to the greater amount of stretch required (based on absolutely no experience remember)... the Mylar would stretch at a much greater range... if that makes no sense, then hopefully this will clear it up. If you stretch any material, the way I see it, it stretches unequally, in some spaces it stretches a lot, in some not so much and I'm guessing it stretches the most right in the middle of two points holding the material in any given lateral direction (I could be wrong here and it might stretch the most at the points of contact and least in the centre but I hope I've made my point clear). SO! What we need to figure out is how much stretch is happening at the different parts of the Mylar on the 40 degree one and then scale it up to the 60. In other words, we need to basically create a piece, which if vacuumed, will have similar amount of stretch at similar places to the 40 degree one.

In the image below, I'm showing my train of thought.

4547

The smaller the vertical field of view, the more we can get away with a simple rectangular piece, the larger the vertical field of view, the more we need to make it bend. I'm not accounting for the fact that the circumferences are different at the top and bottom which would I assume, make the shapes a little bit more funky around the sides but I hope I made my point clear. Perhaps those more in the know might be able to correct what I'm saying and totally discredit it :).

EDIT: Just found this in a patent document:

"It is known for typical wide-bodied cockpits that a 40 degree vertical field of view may satisfactorily be achieved with a spherical mirror of about 3m radius and a spherical screen. A vertical field of view of 50 degrees may be achieved with the same radius mirror, but the screen must become aspheric. For a 60 degree vertical field, not only must the screen become aspheric, but also the mirror radius must increase to about 3.3m."

wledzian

12-12-2010, 03:04 PM

I don't have my raytracer handy, or I'd make some good illustrations for you. I'll include them in a later post.

If the design eyepoint is very near the center, the field of view is limited to about 40 degrees. This is partially due to material limitations - when the mylar is stretched from a conic shape developable from a flat surface into the spherical shape, the arc defined by about 40 degrees produces a stretch very close to the material limits of the Mylar. If you try to stretch more than that, and you pass over the peak of the stress-strain curve and the mylar pops.

There is also the choice in vertical positioning of the eyepoint. If you move the eyepoint downward, that same 40 degrees of arc can cover more than 40 degrees of vertical FOV, because you're physically closer to the bottom of the sphere. Because of the extreme off-axis eyepoint, spherical aberration comes into play more strongly, and the required screen shape gets weird. The volume in which the collimation effect is acceptable shrinks. The distortion band around the bottom edge also increases in width, just due to the varying amount of stretch. Since you're further down in the sphere, the entire sphere has to be enlarged in order to fit the cockpit structure. Also because you're so far down in the sphere, the shape of the unrolled film becomes more curved, leading to a requirement for an even wider sheet.

There is also the choice of horizontal eyepoint position. If you move your eyepoint towards the mirror, the usable portion of the mirror in front of you fills a larger vertical FOV, but the portions to the side fill a smaller vertical FOV. One solution for getting a big vertical FOV is to make a big mirror and sit closer to it. This works well for large commercial sims, as the cockpit structure and windows does a good job of cutting the FOV to the sides anyway. In fact, with each pilot shifted foward and outward from center, each pilot has the largest FOV just outboard of the main windows, just as in the actual aircraft. The screen design gets more challenging, but by no means impossible. Again, though, to fit the cockpit structure within the mirror, the mirror needs to be rather large. As I still haven't found a source of mylar in sizes larger than ~56" without requiring the purchase of an entire 10,000 lb production roll, that is the main limiting factor at the moment.

mikesblack

12-12-2010, 09:05 PM

wledzian,
Sending you a pm.
Mike

geneb

12-13-2010, 04:39 PM

Wayne & I got a lot of really good design work done this weekend - when I've got time to re-create the model in Inventor, I'll post pics. (I should note that he DOES know how to use AutoCAD! *laughs*)

The big win this weekend was a solid grasp of the geometric limitations of the simulator cab. Because we're limited to the size of mirror we can make with a 56" wide roll of Mylar, that kind of dictates what cockpits can be built for use in the system. Right now the tiny GA 2 placers are an easy fit. The Cessna 152 has got tons of room and the 172 will fit as well. Both wouldn't be good choices because they're high-wing and the mirror goes from 0 to 40 degrees, which is far less than what you can see out the side windows. Any one of the "standard" low-wing GA aircraft should work though (Piper, Mooney, & Beechcraft are the popular ones). Wayne even managed to squeak a King Air 200 into the space available. It would require a special 3D model in order to show the wing & nacelle on each side, but that's fairly easy to do.

We also were able to cost-reduce the framework quite a bit. This is a Good Thing(tm). My original design was to use 12mm Baltic Birch throughout with 3/4" plywood partial width doubler layers in specific places.

We backed off the 190 form to 180 in order to make it break down to three sub-assemblies that would be easier to manage - the design goal is to create no component too large to navigate the interior spaces of Wayne's house. :) The new design uses 7/16" OSB for the top, bottom and end plates and 3/4" plywood for interior screwing rails. Each segment will bolt to one another using 1/4-20 bolts. The center segment and "interior" ends of the left & right segments will be under-sized along the mirror arc in order to prevent any contact with the mirror as it forms. The segments will also use two 1/32" rubber gaskets in order to prevent leaks.

The segments will have multiple coats of paint in order to make them as leak-proof as possible. (A high vacuum will actually pull air through OSB and some other materials like MDF)

When I post pics, a lot of my rambling will make more sense I think. :)

g.

Atomic_Sheep

12-13-2010, 10:34 PM

Wow, Quite disappointing in regards to the 56" maximum size. I've got a got a feeling that cullimated guys should come together and purchase the big roll and then use what we need and either try to sell the rest to farmers or something, or simply keep it and sell it as other guys decide to get into cullimated displays.

Sounds good geneb, can't wait to see your progress. I'm probably going to do something similar to your desing i.e. build it in 3 parts for some flexibility if moving is needed. I've just got one question, I can't remember reading your solution to the back of the frame i.e. when you create the vacuum, do you have some sort of flat backing that you have attached to the formers to which the mylar conforms when the vacuum is created or do you simply create a vacuum and use whatever shape the mylar naturally forms? I was thinking making the whole thing out of fibreglass but I then realised that fibreglass isn't exactly flat and finishing it off to make it flat would be a nightmare. I then thought of simply creating a large number of formers such as the ones that you have and simply sticking them together side by side and creating a solid wooden spherical strucutre type backing but then I realised it would be insanely heavy and totally not appropriate for me considering I want to in the long run create a motion platform. Carbon fibre would just be too expensive so that's not really an option either. Any ideas in this regard?

wledzian

12-14-2010, 12:02 PM

When I say "full production roll", I'm talking the full, ten-thousand-pound spool.

The vacuum is used to form the mylar. It is not used to hold it to a surface. The volume behind the mirror is hollow. That being said, you can build your frame from whatever material will be strong enough to stand up to the loads without significant flexing. Fiberglass would be a good choice, if you're comfortable working with that material. The required stiffness could be achieved fairly easily by making it a foamcore structure.

Atomic_Sheep

12-14-2010, 12:27 PM

When I say "full production roll", I'm talking the full, ten-thousand-pound spool.

Yep, I understand which is why I said we needed to pool resoruces to get it. Sure, that's a lot of people! But still :P. Not totally serious about that, I'll admit.

Do you think that the guys in the video (forgot which company they were from) who were doing the 777, do you think/know their mylar conforms to the backing material? I've still got a lot to learn about Collimated displays, I've only recently started reading about them so I don't know quite a lot of basic stuff. I remember there was mention of this in the earlier threads but I didn't find a subsequent response which I thought answered that question. I suppose the fact that there was talk of a feedback loop indicated that indeed, they were calculating some sort of optimal value for the amount of volume of air/pressure in the 'vacuum' to which the system tried to revert back to throughout the operation but I'm not sure.

wledzian

12-14-2010, 01:45 PM

The mylar does not conform to a backing material.

The mirror frame is hollow. The mylar is stretched into final form by the vacuum. Except for the the edges where it attaches to the frame, the mylar does not touch anything.

For the prototype mirror, we used an adjustable bleed valve on the back of the frame. This was adequate for our purposes, as we haven't used the mirror for any long period of time. We've had to slightly adjust the valve each time, and this would be very inconvenient once the final version is built. A feedback device that operates purely on pressure differential may not work adequately, as mylar does return to its original form somewhat, but not completely, and has the odd property of slowly stretching back to its final shape over time. That is to say, if the vacuum has been turned off for a while and turned back on, it will require a stronger vacuum to draw it down initially, but will continue to stretch a little bit and require that the vacuum be relaxed a little as it stretches. Gene's got a concept for a contact position sensor based on a fine copper tinsel. I've got a concept for a contactless optical sensor based on phototransistors. Both concepts will modulate the vacuum pump and a small bleed valve in order to maintain the mirror at the proper position.

geneb

12-14-2010, 03:01 PM

The cool thing is that both systems could co-exist and might even be able to work together. I suspect that the robot builders have a lot of experience with using photo transistors and could be of some help in perfecting the concept you want try out.

I checked out using the little ultrasonic sonar units the robot builder types use, but the ones I found didn't appear to have the resolution we'd need. I should check with the Arduino guys and see what they'd recommend for very precise distance-to-surface measurement. I'm going to need to find a solenoid valve too - that silly thing I bought from Surplus Center.com was waaaay to tiny to use for anything. Although, if the pump has a check-valve in it, we might not need the secondary valve - the pump itself would prevent vacuum loss when it was turned off.

Lots and lots of fun stuff to think about.

g.

Jordan Farmer

12-14-2010, 03:30 PM

Hi guys, just to have my say on the vacuum side of things! Im a farmer, as you may have probably guessed, and use vacuum pumps on a daily basis for the milking machine. We have now got 2 robotic milking units, which use a variable pressure pump, which basically pumps ata much higher rate while pulling the desired vacuum, and then when it has the pressure, it slows down, until it will just maintain that pressure, its also extremely quiet, i often dont realise its going, so n a small box, it would be almost silent.

This may help you, it may not, but do look into the vacuum pump solutions that us farmers use, theres been alot of development into this area, and im sure you will benefit from it!

Jordan

geneb

12-14-2010, 04:02 PM

That's an interesting idea Jordan. The only issue I can think of is that the required stop point would change over time, but a differential feedback mechanism might solve that.

The pump I bought is small enough to fit in the palm of my hand. It's 110v AC and doesn't have much of a volume rating, but I'm hoping it can pull at least 6 PSI.

g.

Atomic_Sheep

12-15-2010, 01:44 AM

I'm no expert in physics but based on my limited knowledge, I've got a feeling that no sonar based solution will work (but I'm basing that off the fact that mylar is quite thin. Maybe this is what you were referring to when you said sonar has inadequate resolution but I'm no exper in the area)... well at least no sonar based solution that is cheap. Pretty sure optical solutions are on the right track and I think it's easier to get right also or maybe I'm just more comfrotable with this tech. Either way, this vacuum revelation has just made me realise that this collimated screen will be much harder to make than I first anticipated.

The other question that I've thought of in light of this information is, is it possible/advantageous to have mutiple vacuum sources i.e. you have pumps in various locations? The way I see it, where the mylar is attached, it will not stretch at all, so there will be differences in tension in the mylar. The only simple solution that I see to this would be to approximate where the mylar should be stretched to from the begining and then attach it in a stretched state. Based on the CAE video, I cant help but feel that this is what is happening when the guy goes over the whole screen on the ladder. You can see distinct vertical lines in the mylar that are equally spaced which to me indicates that the material has been stretched at predefined intervals. So if this is the case, then I suppose basically one vacuum source will be enough but maybe distributed sources would allow greater control over the shape of the mylar?

vyper883

12-15-2010, 04:33 AM

I've been thinking about this nasty problem for the last three weeks. So much so that I didn't do a thing with it today - I gave my poor IBM 5160 some quality time instead. *laughs*

First, you need one of these...

http://www.diy-cockpits.org/coll/images/mirror_frame.jpg

...but that's not all. :)

I'm going to try to get a frame that will fit into the one shown above to retain a solid skin - hopefully I'll get to it tomorrow.

One thing I noticed about the video from How It's Made - the mylar _crawls_. I've only seen that when a material is being drawn against a solid surface. I strongly suspect there's either a solid skin with a Metric Buttload(tm) of tiny holes, or there's a gas permeable solid like MDF there. Fortunately, I've got me a little gadget that's perfect for drilling holes in Metric Buttload quantities. :D

I should note that the frame in the picture above is a 60 degree wide slice of a 48" radius circle. It's 40 degrees high. The top is at zero degrees. This is a good size for a practical test. It also means that if it works, I only have to build two more to get 180 degrees. :)

g.

Hi Gene :)

Up until now, I've been lurking here for a long time, and I have followed the collimated topics from the very beginning. I'll introduce myself officially in the proper thread later. Great job on your prototype !

I've watched the how it's made video dozens of times, and that JUST what I was thinking too. It crawls as if it was being drawn onto a surface. However, I highly doubt that there are any permeable materials into play. IMO, even the slightest of pin holes would probably show up as some kind of distortion on the mylar surface. I think what is happening is:

The mylar has the greatest slack in the center. That would allow the center of the mylar to get drawn down onto the surface FIRST once vacuum is applied, and gradually get drawn down until it reaches the outer edges. That way, there would be no air pockets trapped underneath the mylar. Also, there may be a possibility, that the frame that holds the mylar, might be adjusting the rate of tension somehow, via an automated, or passive mechanism, during the vacuum stage, to allow said gradual contact of mylar, from the center to ouside edges. Of course, this is JUST my theory, but one that may fit the facts.

On the other hand, the mylar itself, may just be thick enough NOT to distort, if there IS some kind of perforated forming block with very tiny pinholes on it's surface. The only thing I TRULY believe after watching that video over and over, is that the mylar ultimately is being drawn onto some kind of surface. As you've said before, the properties of mylar itself, do form a great image, but in time as it is streched and released, it starts to develope more and more slack, that would cause undesired geometric changes in the image over time. To get a constant image every time, it would only make sense to me, to have a permanent forming block behind the mylar. Just my opinion though.

wledzian

12-15-2010, 01:27 PM

The other question that I've thought of in light of this information is, is it possible/advantageous to have mutiple vacuum sources i.e. you have pumps in various locations? The way I see it, where the mylar is attached, it will not stretch at all, so there will be differences in tension in the mylar. The only simple solution that I see to this would be to approximate where the mylar should be stretched to from the begining and then attach it in a stretched state. Based on the CAE video, I cant help but feel that this is what is happening when the guy goes over the whole screen on the ladder. You can see distinct vertical lines in the mylar that are equally spaced which to me indicates that the material has been stretched at predefined intervals. So if this is the case, then I suppose basically one vacuum source will be enough but maybe distributed sources would allow greater control over the shape of the mylar?

You are right, there are differences in tension along the edges. There is reasonably even stretch perpendicular to the edge, but almost none at the edge. In fact, this is the main cause of the edge distortion which forms the unusable "dead band".

The vertical lines are just a result of being slightly unevenly stretched during mounting. It's got nothing to do with intentionally stretching at predefined intervals. He's going over the whole mirror with a ladder bit-by-bit to get it as even as he can. If you just attach one edge first, it is very difficult to get the film to lay right, Gene and I ran into that issue if one of us got even a couple inches ahead of the other when attaching the film. If you look at the video of the first application of vacuum on the prototype, you'll see a similar pattern of wrinkles. Distributed sources of vacuum would require separate sealed zones, and would produce more distortion.

Atomic_Sheep

12-15-2010, 08:55 PM

Thanks, very helpful. I'm seriously contemplating purchasing some mylar in the very near future to start experimenting with it a little bit.

SU-GGG Dispatcher

12-15-2010, 09:41 PM

I was doing some mathematical calculations (Pythagoras) yestarday to design a frame suitable for my cockpit , and i discovered a big barrier , it's the "huge Space" .. but i think it would be a great way for the design if we all recognized the validity of it ..

I'm not sure if those calculations are correct or not , but they seems so logic .. correct me if I'm wrong ..

well , my Cockpit width is 165 cm ( Sorry for the non-US unit ) , so this is the idea of the calculations :-

1- Forward- Projection screen's radius
- I began by the base of the Forward-Projection screen , I planned to be as width as the cockpit .. plus say 5 cm , so the light rays would be free of hitting the cockpit , because it's the first task to guarantee that all light rays from the Forward-Projection screen would hit the whole of the mirror totally , and after i guarantee that task , i can plan the mirror radius / widths / etc according to those calculations .. See Picture below !

http://www.mycockpit.org/photopost/uploads/11597/Radius.jpg

2 - Mirror's Radius
- After i calculated the Forward-Projection screen's radius , I then calculated the Radius of the Mirror .. The idea is the Screen would be in a distance from the Mirror less than the focal length , So i first assumed the screen would be 20 cm in front of the focal point , so the focal length would be [ screen's radius - 20 cm = 249 - 20 = 229 cm ] , Now I could calculate the Mirror's radius by multiplying the focal length by 2 [ 229 x 2 = 485 cm ] , See Picture below !

http://www.mycockpit.org/photopost/uploads/11597/Mirror.jpg

3- Mirror's Lower ( Bottom ) width
- The triangle of the lower width , it's base would be the Mirror's lower width that we aim to calculate , as we know the total sum of any triangle = 180 degrees , so as the base angle = 40* , so both the other angles = [ 180 - 40 / 2 ] = 70* .... & see the Picture below !!

http://www.mycockpit.org/photopost/uploads/11597/Bottom.jpg

4 - Mirror's Upper width
- see the picture , i guess it's now clear !!

http://www.mycockpit.org/photopost/uploads/11597/Upper.jpg

Remarks
- The first 30* angle , to draw a latitude of 30 South ( If we looked to the screen as the earth )
- The 2nd 40* angle , because our Field of View ( FoV ) = 40* .. drawing latitude of 70 South .
- The opposite side is the same as above .
- As the half circle = 180 degrees , so the remain angle ( Mirror's Lower width's angle ) would equal [ 180 - {(30* x 2 ) + ( 40* x 2 )} ] ...

Looking forward for your thoughts

Mohammed Sayed

castle

12-16-2010, 01:24 PM

For those who have been following this discussion or anyone for that matter ;-) here is a link to an excellent set of tutorials on how image warping works and techniques for projecting flat images onto curved screen surfaces

http://local.wasp.uwa.edu.au/~pbourke/miscellaneous/stereographics/cylinder/

For the more adventurous, there is source code on the OpenSceneGraph website (http://www.openscenegraph.org/) detailing the mathematics.

JW

Hessel Oosten

12-16-2010, 06:58 PM

And here ....

On this site:

http://www.mod-gmbh.com/Collimated-Display.48.0.html

is an interesting paper about the collimated display principles:

http://www.mod-gmbh.com/fileadmin/user_upload/website_dateien/projects/display_systems/Coll-Sale-Paper.pdf

Hessel Oosten

vyper883

12-17-2010, 07:23 AM

Hi Guys :)

Forget mylar.....
Get a load of this: http://www.youtube.com/watch?v=HIqxdLJo0_Q&feature=related

And THIS: http://www.anishkapoor.com/works/gallery/2007ccurve/index.htm

If you want even more info, just do a google search for "Anish Kapoor C-curve" This guy is a sculptor, so how did he make this? If we find out, then things get a bit simpler. ;)

Matt Olieman

12-17-2010, 07:31 AM

Hessel, Thanks for the links. The last link is VERY interesting. :)

Matt Olieman

SU-Medo

12-17-2010, 09:30 AM

Hessel, Thanks for the links. The last link is VERY interesting. :)

Matt Olieman

I was doing some mathematical calculations (Pythagoras) yestarday to design a frame suitable for my cockpit , and i discovered a big barrier , it's the "huge Space" .. but i think it would be a great way for the design if we all recognized the validity of it ..

I'm not sure if those calculations are correct or not , but they seems so logic .. correct me if I'm wrong ..

well , my Cockpit width is 165 cm ( Sorry for the non-US unit ) , so this is the idea of the calculations :-

1- Forward- Projection screen's radius
- I began by the base of the Forward-Projection screen , I planned to be as width as the cockpit .. plus say 5 cm , so the light rays would be free of hitting the cockpit , because it's the first task to guarantee that all light rays from the Forward-Projection screen would hit the whole of the mirror totally , and after i guarantee that task , i can plan the mirror radius / widths / etc according to those calculations .. See Picture below !

http://www.mycockpit.org/photopost/uploads/11597/Radius.jpg

2 - Mirror's Radius
- After i calculated the Forward-Projection screen's radius , I then calculated the Radius of the Mirror .. The idea is the Screen would be in a distance from the Mirror less than the focal length , So i first assumed the screen would be 20 cm in front of the focal point , so the focal length would be [ screen's radius - 20 cm = 249 - 20 = 229 cm ] , Now I could calculate the Mirror's radius by multiplying the focal length by 2 [ 229 x 2 = 485 cm ] , See Picture below !

http://www.mycockpit.org/photopost/uploads/11597/Mirror.jpg

3- Mirror's Lower ( Bottom ) width
- The triangle of the lower width , it's base would be the Mirror's lower width that we aim to calculate , as we know the total sum of any triangle = 180 degrees , so as the base angle = 40* , so both the other angles = [ 180 - 40 / 2 ] = 70* .... & see the Picture below !!

http://www.mycockpit.org/photopost/uploads/11597/Bottom.jpg

4 - Mirror's Upper width
- see the picture , i guess it's now clear !!

http://www.mycockpit.org/photopost/uploads/11597/Upper.jpg

Remarks
- The first 30* angle , to draw a latitude of 30 South ( If we looked to the screen as the earth )
- The 2nd 40* angle , because our Field of View ( FoV ) = 40* .. drawing latitude of 70 South .
- The opposite side is the same as above .
- As the half circle = 180 degrees , so the remain angle ( Mirror's Lower width's angle ) would equal [ 180 - {(30* x 2 ) + ( 40* x 2 )} ] ...

Looking forward for your thoughts

Mohammed Sayed

SU-Medo

12-17-2010, 09:37 AM

I was doing some mathematical calculations (Pythagoras) yestarday to design a frame suitable for my cockpit , and i discovered a big barrier , it's the "huge Space" .. but i think it would be a great way for the design if we all recognized the validity of it ..

I'm not sure if those calculations are correct or not , but they seems so logic .. correct me if I'm wrong ..

well , my Cockpit width is 165 cm ( Sorry for the non-US unit ) , so this is the idea of the calculations :-

1- Forward- Projection screen's radius
- I began by the base of the Forward-Projection screen , I planned to be as width as the cockpit .. plus say 5 cm , so the light rays would be free of hitting the cockpit , because it's the first task to guarantee that all light rays from the Forward-Projection screen would hit the whole of the mirror totally , and after i guarantee that task , i can plan the mirror radius / widths / etc according to those calculations .. See Picture below !

http://www.mycockpit.org/photopost/uploads/11597/Radius.jpg

2 - Mirror's Radius
- After i calculated the Forward-Projection screen's radius , I then calculated the Radius of the Mirror .. The idea is the Screen would be in a distance from the Mirror less than the focal length , So i first assumed the screen would be 20 cm in front of the focal point , so the focal length would be [ screen's radius - 20 cm = 249 - 20 = 229 cm ] , Now I could calculate the Mirror's radius by multiplying the focal length by 2 [ 229 x 2 = 485 cm ] , See Picture below !

http://www.mycockpit.org/photopost/uploads/11597/Mirror.jpg

3- Mirror's Lower ( Bottom ) width
- The triangle of the lower width , it's base would be the Mirror's lower width that we aim to calculate , as we know the total sum of any triangle = 180 degrees , so as the base angle = 40* , so both the other angles = [ 180 - 40 / 2 ] = 70* .... & see the Picture below !!

http://www.mycockpit.org/photopost/uploads/11597/Bottom.jpg

4 - Mirror's Upper width
- see the picture , i guess it's now clear !!

http://www.mycockpit.org/photopost/uploads/11717/Upper.jpg

Remarks
- The first 30* angle , to draw a latitude of 30 South ( If we looked to the screen as the earth )
- The 2nd 40* angle , because our Field of View ( FoV ) = 40* .. drawing latitude of 70 South .
- The opposite side is the same as above .
- As the half circle = 180 degrees , so the remain angle ( Mirror's Lower width's angle ) would equal [ 180 - {(30* x 2 ) + ( 40* x 2 )} ] ...

-- Those calculations for explanation only , but of course as the upper curve’s latitude increases , the radius increases ….

Looking forward for your thoughts

Mohammed Sayed

Snovadnb

02-28-2011, 04:52 AM

Hello, i read this thread all - cool! I have question:

how did you control vertical mirror radius and horizontal mirror radius ? I construct analog your system, but i can't make vertical radius equal horizontal radius =(

how did you control sphericity?

thanx!

http://www.mycockpit.org/forums/attachment.php?attachmentid=4880&d=1298884381

http://www.mycockpit.org/forums/attachment.php?attachmentid=4881&d=1298884381

http://www.mycockpit.org/forums/attachment.php?attachmentid=4882&d=1298884381

http://www.mycockpit.org/forums/attachment.php?attachmentid=4911&d=1299057594

wledzian

02-28-2011, 11:01 PM

The design geometry is defined by the frame shape, which must lie entirely on the surface of the sphere. When the mylar is first installed, it will have the shape of a cone, and will deform into the spherical shape when the proper vacuum is applied. Until the vacuum is at the right level, the horizontal curvature will be larger than the vertical curvature.

How have you attached the mylar to the frame? Is it just clamped in place? If so, the extra material on the edges may stretch inward unevenly, creating an unacceptable amount of distortion.

For the prototype, we know the vacuum is correct when the mylar makes contact with the internal ribs. Once we see the distortion from the ribs (clearly visible in the photo on page 13, post#128), we reduce the vacuum just until the distortion disappears. For the full-size version, the ribs have been set back, and will not touch the mirror. Instead, we've developed an optical sensor based feedback system controlling a valve box to keep the mirror in the correct position. We'll need to install a temporary "indicator block" on one of the ribs to find the correct sensor reading when the mirror is in position, but once we've established that value, the indicator block will be removed.

Snovadnb

03-02-2011, 05:42 AM

We attached mylar to the frame without adhesive tape or glue.
Only still strip.
It is no good - we understand now =)

Snovadnb

03-02-2011, 05:55 AM

So well, we have two different problem: distortion and sphericity.

wledzian

03-07-2011, 08:22 PM

I just found some great photos - they appear to be of the same CAE sim installation shown in the earlier video.

http://www.fotothing.com/B0B/photo/4920602806627da215d989d52150212c/

vyper883

03-09-2011, 03:05 AM

I just found some great photos - they appear to be of the same CAE sim installation shown in the earlier video.

http://www.fotothing.com/B0B/photo/4920602806627da215d989d52150212c/

You know Wayne, looking at some closeups of those photos (TY BTW-great hi res pics!) I would almost swear, that the mylar absolutely gets stretched across the back surface of the frame when it's under vaccum. There doesn't appear to be much of a cavity for the mylar to to be drawn into, as opposed to your original prototype. (speaking of which I'm awaiting anxiously to see new pics your current iteration )

Seeing it up close in those hi res photos, make my brain think that it makes perfect sense for the mylar to actually be drawn onto a surface, rather it being suspended in a void. In one of the pics, I can judge no more than maybe 2 inches of the relaxed mylar from the back surface of the frame. I could be wrong, and I probably am, and I'm OKAY with that lol. But after seeing those photos, I just can't help thinking it is so. EDIT

mikesblack

03-09-2011, 04:19 AM

Hi-

Thought I'd chime in here.

The mylar material needs to be optically near perfect as it is becoming a lens. Having a surface "push through" would distort the image.

Think of a mylar balloon, forgetting the wrinkles near the edges, the surface is perfectly smooth and so too is the CAE flight simulators as per these photos. The vacume pulls the mylar, or rather the pressure differential allows the mylar to " ballon" out from the rail frames that drape the material.

wledzian

03-09-2011, 03:40 PM

There's not much of a cavity behind the mylar, but the mylar touches only the frame. The structure is spherical as well, probably only larger than the mirror by a couple of inches as you said. As mikesblack mentions, contact with the back surface would produce optical distortion.

The stretched mirror forms what is essentially a big drum head. With mirrors that large, the 'drum' can vibrate at a frequency which produces visible effects. One design goal is to minimize the space behind the mirror, in order to keep the resonant frequency as high as possible. With our prototype (and we hope, with the larger version as well), the mirror is too small to resonate at such low frequencies, so the large cavity is not a problem.

In other news, design work is all but finished, the frame and table parts are all cut. We need to polish some details on the screen design, but the remaining work there is little. I've got other business keeping me from the sim this weekend, but I expect we'll begin assembly on the 19th.