I'm having a bit of difficulty with some cheap RC servo units (being driven
from a PIC).

Every now and then, the servo unit goes into a funny oscillating mode
(frequency the same as the driving pulses). It draws lots of current
(>500mA), and the stiffness of the unit drops off to about zero. If I
change the length of the pulses, the servo moves off to the right place,
and (usually) stops oscillating. I've tried adjusting the amount of
friction in the system, but that doesn't help. I don't think it's a
'hunting' problem, because you can move the servo a long way off it's
correct position without any effect.

The driving pulses are quite stable in length - it's not a problem at the
PIC end, I don't think.

PIC and servo run from different power supplies, Control pulses are between
~1mSec and ~2mSec applied at about 50Hz.

If anyone's got a clue what's happening, I'd be grateful for their suggestions.


Alec

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