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Topic: High precision servo control. (Read 5 times) previous topic - next topic

BigusDickus

Thanks for the responses....
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You don't really mention the end result of what you want to do, so suggestions are limited

The end result is to provide smooth control for a HPA (human powered aircraft)....
http://www.youtube.com/watch?v=YtGEmu0Rdec

I'd like to achieve a resolution/repeatability of about 90 discrete positions in a 180 degree sweep of a servo arm (i.e. a repeatable accuracy of about 2 degrees). My experiments so far indicate that an arduino can easily control a servo to this level, the problem is finding a human input device that allows me to control the arduino equally accurately.

At the moment I recon I'm lucky if I can manage an accuracy of 10 degrees.

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There are 20 turn precision pots
Yes, I've actually played with some of these in my earlier experiments and they do produce the desired results, but a 20 turn pot can't easily be incorporated into a aircraft style control column (not that you knew what I wanted to do with it on my first post)!

I believe the problem stems from the fact that most joysticks use a carbon track pot that only sweeps through only a few degrees, making repeat-ability very hard to achieve. 

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That SparkFun 'joy stick' pot is pretty much garbage as far as resolution and repeatability goes
I know, at least I they're cheap and I didn't waste too much money finding out how bad they are!

Ideally I'd like a lightweight, high accuracy joystick. unfortunately many of the easily obtainable joysticks just use on/off microswitches to crudely detect position, the high accuracy joysticks (from electric wheelchairs and industrial diggers) cost a fortune, so I'm really just left with making something - hence the reason for this post.

Thanks

DuaneB

Silly suggestion maybe, but what about PC flight simulator joysticks ?

Duane B

rcarduino.blogspot.com

stratosfear


Aurora 9 joysticks are available and quite reasonably priced.  The usual difficulty with joysticks like these is they only swing about 1/5 of the total pot travel.  To get a full ADC count, you may need to use an external analog reference. 

Jon

BigusDickus

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what about PC flight simulator joysticks ?

I have tried these, but the performance you get from them isn't always good enough.

Another issue here is weight, the target weight for a HPA is normally less than 35kg, so a 250gram (or more) joystick is significant.

What I'll probably end up doing is using an old joystick and stripping all the redundant switches and plastic housing off it to reduce the weight.

Thanks

PeterH

The problem seems to be finding a type of control that a human can position accurately to one of ninety discrete settings. I suppose you could use a rotary pot with detents (notches) so that it clicked into each discrete position, that would rely on the pilot counting the notches or having a dial to indicate the current position. If you can provide any sort of feedback (digital display of the actuator position?) then you could just use a rotary encoder to move the actuator in steps and not have to worry about the absolute position of the control.
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