Tighting up controls

[jmig]

It looks so sad to see a forum with no posts. Besides, this may be the perfect place to post this question.

I have a DIY control stick, made to represent the real aircraft stick. I use plastic gears with a 1:3 ratio to get more movement in the pot. However, with the long moment (appox 24") the gear slack gives me about 1" inch on either side before control input is seen in MSFS. This makes for a lot of slop in a fighter cockpit.

Anybody, have an idea on how to tighten up the slop? I have already set the FSUIPC slope to +3. Any more and I get a sudden movement from the aircraft. I have my Delta set to 1. I am using a higher grade (Borug) pot, than the standard Radio Shack variety, in order to get better control.

I don't use MSFS to control the inputs. It all goes from the OpenCockpit USB Axes card through FSUIPC.

[Mike.Powell]

One approach is to pre-load the potentiometer shaft with a spring so that it has a torque on it. This keeps the tooth faces of gear on the potentiometer always in contact with its mating gear. You can use a "constant-torque" spring which is basically a spiral clock spring. Alternatively, you can use a pulley and a standard extension spring.

[jmig]

One approach is to pre-load the potentiometer shaft with a spring so that it has a torque on it. This keeps the tooth faces of gear on the potentiometer always in contact with its mating gear. You can use a "constant-torque" spring which is basically a spiral clock spring. Alternatively, you can use a pulley and a standard extension spring.

I don't think the spring idea will work, Mike. These potentiometers have to work in both directions. A spring would only apply tension in a single direction.

The use of pulleys with an idler would probably work. In that way, i could take out any slack.

[Mike.Powell]

The spring doesn't prevent the pot from working in both directions. It just takes up the backlash in the gears. This is the same approach used internally with "string potentiometers".

[spitfire9]

I wonder how hard it would be to take a standard 270deg. pot and make a string pot out of it ?? Add a small pulley and spring to the pot shaft ??

It would certainly be much cheaper than buying a string pot.


I once extended the stick on my MSSidewinder joystick and ran into the same problem. I ended up shortening the shaft so the base of the stick was just under my knees when sitting in the pit,, rather than having the shaft extended to the floor.
In other words I didn't solve the problem.

I saw a picture a while back of a commercially sold extension for a Saitek stick. It was quite eloborate with brackets and pulleys etc. Somehow translating the big movement to small movements the original short stick makes.
I will look for it and post it if I find it.

[spitfire9]

Here is a link to Simcontrols.

They sell that extended sitck and there are some good pictures that may give you some ideas.

Like I said before,, rather elaborate,, there should be an easier way ??

http://www.simcontrol.co.uk/newheli.htm

[Matt Olieman]

Here is a link to Simcontrols.

They sell that extended sitck and there are some good pictures that may give you some ideas.

Like I said before,, rather elaborate,, there should be an easier way ??

http://www.simcontrol.co.uk/newheli.htm


WOW, that's quite impressive!!!! Thanks for the link. Please, someone, go put that in the "Builder Links (http://mycockpit.org/links)"

[Trevor Hale]

It looks so sad to see a forum with no posts. Besides, this may be the perfect place to post this question.

I have a DIY control stick, made to represent the real aircraft stick. I use plastic gears with a 1:3 ratio to get more movement in the pot. However, with the long moment (appox 24") the gear slack gives me about 1" inch on either side before control input is seen in MSFS. This makes for a lot of slop in a fighter cockpit.

Anybody, have an idea on how to tighten up the slop? I have already set the FSUIPC slope to +3. Any more and I get a sudden movement from the aircraft. I have my Delta set to 1. I am using a higher grade (Borug) pot, than the standard Radio Shack variety, in order to get better control.

I don't use MSFS to control the inputs. It all goes from the OpenCockpit USB Axes card through FSUIPC.

Jim the reason there are no posts here, is we just created this forum Yesterday. I assure you that Gwyn (Westozy) will be along to put his $0.02 in worth. shortly. keep your eye's peeled.

[Mike.Powell]

I wonder how hard it would be to take a standard 270deg. pot and make a string pot out of it ?? Add a small pulley and spring to the pot shaft ??


Not hard at all. In fact string and cams are used to good effect in a floor mounted stick I'm working on right now. Here's an almost useful photograph of an early prototype:

http://www.mikesflightdeck.com/images/cyclic9.jpg

This a view from the bottom, so the mechanism is upside down. You can't see the potentiometer, just the wood knob on its shaft just to the left and a bit below the right-most white idler pulley. The bigh chunk of wood with all the bolt heads in it pivots fore and aft with stick movement. The string wraps around the knob a couple of times and turns the pot. The trick is to choose the appropriate diameter of the knob for the radius of the string cam (the curved wood piece just to the left of the knob). With the right diemnsions, a 40 degree movement of the shift results in a 270 degree movement of the pot.

I'm about to start building the third prototype of this project. It will be the project in the "Joysticks" chapter of an upcoming book on recreational flight sims. (Assuming I don't die of old age first. I write sloooowly.)

Random useful facts if you want to go down this path:

Use a Bourns model 6639S potentiometer: low torque, tight mechanical tolerance, 10 million turn lifespan.

Always minimize lateral force on the pot's shaft to allow the pot to live out its spec'd lifespan. That's why the idler pulleys are used.

Use low stretch string. I use 80# woven fishing line.

Use replacement closet door wheels for pulleys. They have integral ball bearings and cost about $5 for a pack of two at your local hardware store. Inner diameter is 1/4" so you can mount them using standard 1/4" bolts.

Use a standard instrument knob for the pot then work your math backward to find the radius of the string cam. I got a couple of nice plastic knobs with non-slip groves that grab the string nicely. (Much better than the wood knob in the picture.)

[spitfire9]

Thats exactly what I was thinking about Mike.

Great idea !

[jmig]

That is an excellent idea Mike. Looks like version three of the control stick may be needed.

Cockpit builder's formula: Cockpit = WIP

[Westozy]

Hi John,

I've only this minute discovered the commencement of this forum. I have had a look at your problem and suggest the following...

I would convert to linear potentiometers, dual carbon track type. I use 75mm long with 60mm travel. I see your roll motion axis probably only tilts left and right about 40 degrees. If you had a small swing arm linked to your axle, it could be directly linked to the linear pot converting every movement of the stick to instant response with minimal components in the drive train.

For pitch you could use the same method. Mount a linear pot on your roll rod and pick up a push/pull point somewhere just up from your joystick's pitch pivot point. This would eliminate all backlash and deadband. Linear pots are much easier to set up than rotary pots in general. This is how I will set up the pot drives in my A320 TQs.

If you would like some sketches additionally to help explain all of this, let me know and I will draw some! I often see gear drives and other complicated methods of interface in peoples sims which are usually avoidable and unneccessary.

Regards, Gwyn

[jmig]

Thanks Gwyn. You and Mike have given me much food for thought. I am 1/3 of the way through a two week bsiness trip. I have time to think, plan, and develop ideas.

[Westozy]

Thanks Gwyn. You and Mike have given me much food for thought. I am 1/3 of the way through a two week bsiness trip. I have time to think, plan, and develop ideas.


I'll make a sketch for you, it might be useful to others too!

Gwyn

[Westozy]

Hi John,

Here's a sketch of what I was thinking about!

Looking again at your set up you could pic up a linear pot drive from your centring piston damper.

Gwyn

[jmig]

Thanks for the drawing. I like its simplicity. Since I am going to be modifying my control setup, I want something that won't require me to disassemble the entire sim. :roll:

[Westozy]

Thanks for the drawing. I like its simplicity. Since I am going to be modifying my control setup, I want something that won't require me to disassemble the entire sim. :roll:

The "KISS" principle is always high on my list!

Gwyn