Need some help from clever builders...

[AK Mongo]

I am trying to find an elegant solution to interfacing a rotary pot with a push/pull cable. I am trying to interface a real Cessna Throttle (and Mixture and Prop) cable to a standard 300 degree pot.

Any great ideas how to do this?

Difficulty...I don't have access to a cnc, and tools are limited to basic hand tools. http://i885.photobucket.com/albums/ac52/akmongo/TPMPotinterface.jpg

Rack and pinion seems to be a commont way to translate linear into rotary motion, but how would I do this if it were the rack that had to move?

[Ronson2k9]

Without going into gearing options you could use a bell crank.

http://shop.artspeedequip.com/images/DSC00688.JPG

You could take a look at push/pull throttle group thread. It uses hand made controls but you could adapt the 'back' end to your real controls perhaps.

http://www.mycockpit.org/forums/showthread.php/17515-Push-pull-controls

In your case though as you are using 'Rotational' pots not linear you would need a worm gear to convert the linear movement into rotational movement

Worm Gear
http://chestofbooks.com/home-improvement/workshop/Machine-Shop-Work/images/Fig-272-Simple-Worm-Gear.jpg

You could find the parts you need at a hobby shop as they have quite a bit of that for both model railroading and RC cars.

[AK Mongo]

Without going into gearing options you could use a bell crank.

http://shop.artspeedequip.com/images/DSC00688.JPG

That was my first thought as well. The problem lies in the large angular rotation needed, and the stiffness of the cable. The cable does not want to bend or flex, so I am looking for another way. Thanks for the suggestion though!

[Ronson2k9]

You could always connect another cable (bicycle cable etc) to that cable to make it a more flexible movement.. In any case I'm thinking your best bet is a worm gear. This will let you rotate to get movement as the controls work in that fashion as well. That's what the button is for on the end of the control. It's to make the control locked in linear movement so that rotational movement will move the control. Pushing the button releases the lock and lets you move the control the linear fashion.

I calculated it out for you. You will need a 28mm diameter gear to get 360' travel from a linear 90mm movement.

D = C/pie

You should be able to find something like that at your local hobby shop (Model Railroading / RC Car) they both employ such gearing in various forms for the models. I tried looking up 28mm gear and got a bunch of photography stuff. 28mm is a popular lens size. Model railroading especially uses worm gears. You should be able to adapt a threaded rod for the shaft of your movement. It will need to be long enough to be held in place.

NOTE: The Throttle is reversed to the other controls. That is you PUSH to open. So you will want your pot to rotate in the opposite way to the others. You might be able to map that in FSUIPC perhaps I'm not sure though. I'm thinking though that reversing the direction of rotation could be easier.

[kermit]

Hi,
Why do the hard way?
Just spend a pound/dollar/yen and buy a sliderpot,
its very easy to connect.
If you look at the Simkits website you can see how it is connected.
I have done it myself, only using household tools.
greetz

[AK Mongo]

Without going into gearing options you could use a bell crank.

http://shop.artspeedequip.com/images/DSC00688.JPG

You could take a look at push/pull throttle group thread. It uses hand made controls but you could adapt the 'back' end to your real controls perhaps.

http://www.mycockpit.org/forums/showthread.php/17515-Push-pull-controls

In your case though as you are using 'Rotational' pots not linear you would need a worm gear to convert the linear movement into rotational movement

Worm Gear
http://chestofbooks.com/home-improvement/workshop/Machine-Shop-Work/images/Fig-272-Simple-Worm-Gear.jpg

You could find the parts you need at a hobby shop as they have quite a bit of that for both model railroading and RC cars.

Afraid worm gear would not be the answer, as the cable does not rotate. It goes strictly in and out (left and right in the line drawing). Pretty sure that the answer lies in either a rack and pinion, or in some way to devise a slotted cam that an attaching mechanism could ride in, to spin the pot but allow the cable to have little deflection along any axis.

Any other ideas based on that?

[AK Mongo]

Hi,
Why do the hard way?
Just spend a pound/dollar/yen and buy a sliderpot,
its very easy to connect.
If you look at the Simkits website you can see how it is connected.
I have done it myself, only using household tools.
greetz

I have been thinking about that, and may go that way if need be. I want to be able to use the full range of motion for the controls, which are more than 60mm. I was also worried about durability on the slide models. Mike Powell's pot tutorial mentions that can be an issue. Have you had problems with yours?

[Perik]

Hello

You could take a look at the following threads about String Potmeter
made easy:

http://www.mycockpit.org/forums/showthread.php/14651-home-made-stringpot?highlight=spring+potmeter

http://www.mycockpit.org/forums/showthread.php/15402-String-Pots.....?highlight=spring+potmeter

[Ronson2k9]

Those seem pretty cool to me too. The friction on the control would need to overcome the springs force though. There is probably a way to reduce the spring force so it still moves the pot but doesn't pull on the control and increase the friction a bit so it stays put but can easily be moved.

Reduced spring so you don't need so much friction.

Very interesting stuff though just the same..

Rack and Pinion was what I was thinking of I just didn't know the name till I looked it up. I was thinking the worm though from a rotational standpoint but your right about the cable from the control. That worm action must happen up front ?

[Buddym]

There's a thread somplace, I will go find it in a minute.... where a guy built a throttle control with Legos. I kow it sounds funny, but it's very cool! He translated the linear motion to rotational movement by placing a spur gear on the potshaft and used a rack gear mated to it...

LINKL

http://www.simpits.org/articles/lego_thr/lego%20quadrant.htm

[AK Mongo]

Rack and Pinion was what I was thinking of I just didn't know the name till I looked it up. I was thinking the worm though from a rotational standpoint but your right about the cable from the control. That worm action must happen up front ?[/QUOTE]

Correct.

The handle rotation on the Prop and Mixture controls does not cause the working end of the cable to spin, only move in small increments.

[No Longer Active]

To put it simply, just use linear slide pots attached to your levers and leave out the rotational adjust feature to keep it simple!

Cheers,

Alex

[Ronson2k9]

Well Alex as it's happening up front he will get that too. It's already built into the control. Perhaps there is a way to disconnect the cable from the control and use a different one though if space is a problem and the cable doesn't flex that much? I've got my mind on building one myself so it's flooding over from to time time .. sorry.

BTW guys my remade version of the C172 => C185F of the panel drawing is nearly complete. Based on my calculations the 185 pit is about 10 inches smalled then the 172. The MIP is about 31" across. I had thought it would get a bit bigger then the 172 but smaller then the 206. Also Alex you had the prop / engine mix in the wrong place. Prop goes beside the throttle. I think because they are both related to RPM.

The more I dig into Paint.net the more I like it. Especially the bezier curves.

[Westozy]

This is an easy one. I have used this method to interface the slide motion of my rudders to a small 10kohm rotary potentiometer. I would avoid the use of bell cranks as you will end up with a non linear signal. Slide pots are a good option and they can be mounted upside down so they avoid collecting dust in the tracks, they will last quite a while and they are a cheap option.

To connect a slide throttle to a rotary pot there is a simple solution - attach some fishing trace wire to the end of your throttle slide and then wrap the wire around a small drum on the pot (like a cotton reel shape). Wrap it around the drum about three times and then attach the loose end to a fixed point using a light spring to keep the tension on. When you buy stainless steel fishing trace wire it usually comes with small crimps for making loops on the ends for connecting swivels etc.

To calculate the drum diameter it's good old Pi that helps, I will use 3.142 for Pi and explain the calc. A pot needs to rotate about 3/4 of a circle, usually pots need to rotate about this much to utilize it's maximum efficiency so we need to work out what size circle has 3/4 of it's circumference equalling 60mm.

4 x 60 = 240, 240 / 3 = 80mm (You need a circumference of 80mm)

To find the diameter - 80 / 3.142 = 25.48

You need a drum diameter of 25.48, this is close enough to 1 inch in that measuring system created in the dark ages lol

This will provide a true linear signal from a rotary pot and the wire won't slip if it's wrapped around the drum about three times.

Hope this helps!!!

Gwyn

[AK Mongo]

"To connect a slide throttle to a rotary pot there is a simple solution - attach some fishing trace wire to the end of your throttle slide and then wrap the wire around a small drum on the pot (like a cotton reel shape). Wrap it around the drum about three times and then attach the loose end to a fixed point using a light spring to keep the tension on. When you buy stainless steel fishing trace wire it usually comes with small crimps for making loops on the ends for connecting swivels etc."

Gwyn,
I love this idea...it is thrifty and clever, exactly what I was looking for! Has the advantage of being able to use parts I have lying about instead of using more cash. Would the "pulling" force from the spring or wire cause the pot to fail due to sideload? Can't imagine those things have substantial bearings. Any thoughts?

[Westozy]

[QUOTE=AK Mongo;102105
Would the "pulling" force from the spring or wire cause the pot to fail due to sideload? Can't imagine those things have substantial bearings. Any thoughts?[/QUOTE]

There will be no load on the pot, the light load from a fine spring will all be inline with the wire! The only load on the pot drum will be the wire itself gripping it!


I---------_____________O___________ /\/\/\/\/\/\/\/\/o

Throttle......................Pot........................spring


(how's that for a quick sketch!!!)
Gwyn

[flatlandpilot]

is it possible to make something like this:
http://flatlandpilots.nl/coppermine/albums/userpics/10002/normal_DSCF1536.jpg

travel_dist. = (300/360) * 2 * pi * r

btw if you use 2 pot meters, but only connect 1 electracally,
than you only have to find 2 knobs with the right diameter. (or a little bigger)

potmeters with a metal shaft are bit more durable.

[AK Mongo]

Another great idea! Knew this was the right forum for creative mayhem!