This has been tested and the gearless system works so far, with no slipping. It is a simple setup:

1.Thread rod
2.Dowl Rod
3.Rubber O-rings
4. 1/4 Inch Bolt with Ball point pen roller
5. 1/2 inch x 1/8 flat aluminum holders- No drilling needed, just use bolts.

Throttle action is very smooth, but the  prop pitch (black) adjustment needs to be more angled, as it does not get enough leverage. Basicly, this thing does work, with out the hassles of gears. The thread rod grips the rubber O-ring very well, and the O-ring allows for some minor imperfections in the Dowl rod wheel when drilling a center hole, (but not much!) The dowl rods are not glued on, just friction fit, so if they wear out they are replacable. The bic pen roller/1/4 bolt is adjustable on the Aluminum mounts. Just the two items hold the mounts together. The switches in the corner are for Mags and Starter Button. Hole in the top of throttle (Grey) is for WEP switch. Now to hook it up for real! Fun fun!! This can be done  for about $50.00 or so..

Very ingenious, and well done! Bet it'd work even better w/rods with parallel grooves, instead of a helical groove (try finding that, though!)...
Only other recommendation I have is that you might try to groove those rollers so the O-Rings can't slip off too easily (or did you? Hard to tell). Or better yet- rubber rollers, with a bearing inside (rubber casters). But what the hell- that's a cool mechanism, built for almost nothing!

I have a few questions. What are you using for an interface? and, how are the dowel-rod wheels held onto the potentiometers? do you think this could be done with slider pots? are you planing on covering it with some kind of box?(just curiouse)

Im seriosly considering building one of these, but for a twin.

This is just the test bed, I will be covering this/better setup. I will post a materials list here soon with some assemble pics.

The dowls are held on by friction only. The hole has to be drilled out from both sides centered. I assume there is a bit of off shoot, and that gives a real tight fit- otherwise you need to glue in a scrap of paper or something.

The interface is a joystick extension. Thats the 'fun part' look up: "How to build a throttle" flightsim.com
They have the great articles on that, you need to  D/L it and save it...

There is a P-51 throttle setup on the 'next page " over.
I dont see why that couldnt be done with this system.

I dont think this will work well table mounted. I think it will need its own "stand" so it can hang off the side like that anyway.  That mixture lever needs to be redone also, -to short.

The shortage of length in the slider pots could be compensated by mounting the thread rods closer to the central axis, thereby reducing the movement on the rods.

but slide pots are much more expensive than regular pots. atleast where I live...

-SAto
http://duckparty.no/pit/

I just found something that could work very well with this kind of setup.

http://www.rdpe.com/displacement/lvdt/lvdt-principles.htm
Apparently these are easy to make yourself are linear and work by movement of the arms directly withouth the hassle of rollers and pots.

Also there is almost no wear on these things and they are very accurate compared to cheap pots.

Mikes Flight deck has some info on building them and circuits to support them as well:
http://www.mikesflightdeck.com/lvdts.htm