servo moves unexpectedly

I've got four flex sensor inputs running four servo outputs.  Three of them work just fine.  

The fourth, which is a more powerful servo to open a puppet mouth, is unpredictable.  If you move the flex sensor slowly, all is well.  If you flex the sensor a couple of times in quick succession, however, the servo opens the mouth all the way before returning to where it should be.

Any ideas?  It's a glitch that makes lip synching quite difficult!

Have you tried it with no load to determine if that's what's giving it the shakes? If it still happens with no load on any of them, I'd be thinking it was more likely to be a software thing...

Previously Fionnuala McMullin wrote:

Any ideas?  It's a glitch that makes lip synching quite difficult!

Check the power at the servo connector for glitches.  If the servos, and this large one in particular, are dragging the power supply down too much, it could cause the servo or even the controller behave in undocumented ways.

That this one servo is large, and that the problem occurs with a lot of movement, suggest that it might be a power problem.

Try supplying the servo VIN from a separate power supply and see if the problem goes away.  If it does, then it's most likely not a software problem.

ok thanks for that.  Now it's got another problem.  It's set up so input0 drives servo0, input1 drives servo1 etc. 

It was doing fine until about 5 minutes ago... I haven't changed any of the wiring  but now input1 moves servo0 and input0 doesn't do anything at all!

Well, that, I don't know enough about to advise you on, substantially.

I assume you've rebooted since the off-by-one problem surfaced and that it didn't suddenly start working again afterward.  You say there have been no hardware changes between when the right input activated the right channel and when it became off by one.  Have there been any software changes?  Maybe it's doing exactly what you've told it to, even if it's not what you mean it to.  Not knowing your code, I can hardly even guess.  For all I know, you could have been changing things trying to resolve the upset issue.

I'm not aware of any issues with the ADC or servo drivers getting out of sync.

Changing where the power comes from has no influence on this new situation in any way.  Ie: changing it back won't fix it.