Question about collimated display systems.

[trevj]

Hey guys, I am happy to have found this thread via google - some great info here and some great work. One thing I am curious about regarding the rear projection screen: has anyone tried the vacuum method for creating the screen as well? I'm thinking a latex sheet for the membrane, and a glass panel for the back surface could give nice results.

I also wonder also if using some type of cloth which is impregnated with clothing starch in conjunction to the latex membrane might yield a cloth screen that would retain the correct shape when dried even without a vacuum. This might get tricky, although I am betting a similar technique would work really well for creating a front projection solution if you used layers of plaster impregnated cloth and formed it over the membrane. If this has been talked about already, I'm sorry, I haven't gotten through the entire thread yet.

[ts11iskra]

Wayne and Gene,

Like everyone else I'm overly impressed with your accomplishments; simply amazing. Like many others, I too want to build a collimated display for my simulator.

I've quickly reviewed your postings and looked at your videos online but there's a lot to take in. I'd like to reach out to you via email if acceptable?

For the sake of the thread, I am wondering if there is a better method for applying and then holding the vacuum? One of the thoughts I had was to wrap the back of the Mylar mirror structure (the wood and particle board) in Boating Shrink Wrap. I've been watching a few videos and it would seem to me that the material would make an excellent seal. If you wrap the entire mirror structure in this and create a seal all the way around would it hold? The term they use when wrapping boats is to "weld" the joints which can be done by overlapping joints, heating them and running your glove wrapped hand down the seam. Takes seconds. The shrink wrap should give it an excellent seal and professional looking finish. I see you use a shop vac and realize there is a lot of volume of air to remove from your structure but I'm wondering if the seal were 100% would a smaller vacuum pump with ample time do the trick? A simple vacuum gauge with an upper and lower limit switch could be used to maintain it. I had a vacuum pump years ago for automotive air-conditioning work and it was very quiet.

For that matter it might seems to me that the boat shrink wrap could be a good material for building the screen as it is white and will wrap tightly when heat shrunk. The only issues, the unknowns for me at this point is that all the samples I've found so far are glossy and I don't know how that would work or if it would create visual deformities but is still might make an excellent first layer. Perhaps it would take a coating of flat spray paint?

Well, I'm going to follow in the path you guys blazed here.

[geneb]

The idea has merit, but it may be overkill.

I learned in February that the way Wayne & I are doing the mirror is just about dead-on the same way the commercial guys are doing it. The UK simulator manufacturers tend toward a constant speed vacuum source and a bleed-air valve, very similar to the setup we built. (right down to how they detect the position of the mirror!) US firms tend towards a variable speed vacuum source. This is next on the experiment list. I'm hoping the variable speed system works well because based on my fiddling around with a speed controller, it's a LOT quieter than the bleed-air system. I'm hoping it's actually easier to tune the PID for it as well.

As to using the boat wrap for the screen - that might be a pretty interesting thing to experiment with. The only issue I can think of is that because it's heat-shrunk, it will follow every little shape defect in the screen.

Can samples of the material be had fairly cheaply? I've still got the original screen we built for the prototype and it would be interesting to see how it looks on that.

I wouldn't worry about the glossy-ness of the material though. You go over it with some 000 steel wool to roughen the surface, clean it carefully and then shoot it with whatever paint you'd like.

g.

[arnolde]

Hi Guys,

Just imagine, if you could had a supplier for bigger Mylar sheets, what size would you need/want if you wanted to build another, bigger mirror?

regards,
E.

[wledzian]

We have found a supplier. How big are you imagining?

[arnolde]

upto 12 feet wide

[wledzian]

for a 12 foot wide mirror (6 foot radius), you'd need about 24 feet of 82" mylar.

[arnolde]

so does that mean, the largest piece of Mylar you'd ever want is 7x24 feet?

[wledzian]

No - a 6-foot radius mirror would barely accommodate a C172-sized cockpit. If you want to put a collimated display around an airliner cockpit, you're probably looking at ~9 foot radius minimum, or ~36 feet of 120" mylar.

[arnolde]

Which gets very close to a commercial mirror size... and price
Well anyway... if anyone here wants wide Mylar (4-12 feet wide, 20-50 feet long) then feel free to ask me.