On Wed, 27 Jun 2012 08:32:30 -0500, Lloyd E. Sponenburgh wrote:


(...)

Nonetheless, I was able to determine that the motor was not actually
rapidly spinning; it was creeping at about 100rpm, but "singing" or
"ringing" at the PWM switch frequency -- just without any real power or
speed (full throttle). I checked the brushes, and they're like new.

'Sounds like the controller is current - limiting; narrowing it's
PWM pulses because it thinks the motor is shorted.

--Winston