Rob, even if you build or buy an electronically REGULATED speed control, the actual rpm of the motor is never constant. I know from experience with my camera tracker & it has hardly any load on it & the output pulley rotates once per minute. You have to keep adjusting. Really the only way is to clock/step your platform for accuracy. I built a reg. speed control for a member who made a complete refractor, gearbox, mount and tripod,(A1 fitter & turner), but he still has to make very slight adjs. to the pot to keep the t'scope centred.
I've dabbled in electronics for about 40 yrs. and am still larnin'.
See pic of camera tracker drive.
Just the facts m'am.
