Don't think it's a feedback error so much as carbon deposits on the power valves which make them harder to turn.

The great / bad thing with DC motors is that the more resistance there is, the greater the torque they develop but of course this means more current flow.

That's why they use them in diesel / electric trains - massive torque.

In our application, the motor will try to turn those valves as directed until they shift or the PGM goes pop as it cannot supply the current the motor is drawing.

The answer is an inline fuse / circuit breaker, and is something I've never got round to doing though I've had it in mind for far too long!
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