Johnny

I had just about the same problem, two SH81s burned the moment I turned the switch on the airplane, what the? it was working just fine before, after talking with a friend we end up concluding that my battery a 5 cell pack was gaining strength and like Gordon said " Don't look at a 5 cell pack battery like a 6 volts batt. but instead look at it like a 5 cell pack batt. that could go as high as 7.5 on voltage.

My servos were attach to a BVM smooth stop valve, no binding at all, when the servos burned was when I turned the switch on.

I solve my problem by adding a regulator to the system, since then not a single glich. I have a 4.9 regulator, I have it because it was given to me by a friend, but I will be getting a 5.9 volt regulator in the future because I know the HS81 are OK with the 6 volts.

I hope this helps.