Anyone familiar with desktop flight simulator hardware will no doubt be aware that commercially available throttle quadrants are seriously overpriced, unless one is ready to make do with a cheaply made unit that falls apart in short order.

After drooling over images of real Boeing 767 throttles shown in the website Airliners.net, I decided a few moons ago to try and make a rugged, life-sized throttle quardant whose levers moved with the right tactile feel, to enhance the realism quotient beyond what is on offer with those commercially produced units out there.

The hardware for my home-built twin-engine jet throttle was constructed by a local machine shop owner, whose main source of income comes from repairs done to ancient farm tractors, which explains the, ahem agricultural look of my rough-hewn prototype. Since I am after realistic feel and response to begin with, polishing the apperance of this unit will come later after the bugs have all been ironed out.

All levers are connected to 100Kohm potentiometers, via slotted retaining nuts. The pots are fitted to brackets made of thin and flexible squares of cut tin-can, so that imperfections in the rotary assembly do not transmit stress on the pots themselves, but rather defelect the flexible brackets to which the pots are mounted, which are shown in the closeup photo.

The rust and dust in these pictures comes from this project sitting on the machine workshop table for a few months, while other priorities placed this project on hold.

Now, to the meat and potatoes of the design. From left to right, the following flight control levers are connected to a 100K pot each: Elevator(Stab) Trim, Rudder Trim, Speed Brakes, Left Engine Throttle, Right Engine Throttle, Flaps Selector Lever. Piggy-backed on each of the engine throttle levers are the left and right thrust reverser levers, which actuate momentary-on buttons, thus giving a total of 6 analog axes, and two switches, which is the maximum number of axes that Windows can handle.

Now, since those 6 levers only rotate through about 30 degrees at the most, I expected the wipers to traverse only a hopefully useable fraction of the resistance available on the 100K rotary pots, and from tests, I found out that there was on average a 200mV voltage deflection at the potentiometer outputs, using a 5 volt power supply. To obtain the 0 to 2-volt deflection I would need to feed into the USB interface board that I ordered for this task, I utilized a non-inverting opamp amplifier with a gain of about 11 for each lever, as shown in the attached image.

The USB interface board is chose is the nanoboard from UltiMark, which seemed ideally suited to the task. The problem I am having is that the output from the pots has been erratic, and so far I have only been able to get one of the axes to produce the response I expect to see in my computer’s game controller calibration screen. I didn’t include any caps from Vcc to ground on my LM2902 opamp chips, since this is a simple DC amplifier setup, where noise should be of little concern.

With this buggy behavior so far, though, I am beginning to wonder if there is something fundamentally wrong with the circuit I put together. I was initially so sure this idea would work that I even went ahead and ordered up a batch of 3 PC boards from Express PCB. Now I am not so sure, and so I thought I’d go ahead and let the experts here look over what I’ve cobbled together so far, in the hopes that someone far more knowledgeable than me might be able to spot the error or errors in this setup. Any pointers would be much appreciated. Thanks in advance.

PS I have so far been unable to find a way to show here the PCB layout I had made by Express PCB. I'll keep trying to solve that, in case there is an error I missed in that step.

 

My first thought is dirty pots, considering the gunk on the rest of it. A shot of good pot/tuner cleaner is in order.

I would also put the decoupling/filter caps on the supply.

Is the cat for instrument flight? (They always land with their feet down )

Nice project.

 

Thanks for the quick reply John. I'll take an air-hose to the pots, and also add the decoupling caps, just in case that might be the source of my troubles. Sure wish I'd made provision for those caps on the PCB when it first occurred to me that they might be needed.

 

Compressed air can generate a huge static charge that can fry other circuits. Better to use tuner/pot cleaner in an aerosol can.

 

I'm glad I read your caution before I went ahead and used air line, John. I truly didn't know that such damage was possible. Aerosol it is then, fer sure.

 

As I scurry to add decoupling caps to my board, as recommended by John, I sure would be grateful if anyone else with the know-how can alert me to possible errors in my circuit schematic, before this topic gets buried under the continuing avalanche of other projects here.

Much thanks in advance, and apologies for the crude appearance of my throttle quadrant. I hope to perfect the function of this monstrosity, before I work on the form and aesthetics.