There exist ancient designs for DC motor control circuits that can make a motor run at constant speed regardless of load until it runs out of, er, smoke. National Semi offered the circuit in a chip for a long time, now discontinued for a long time. In all such cases, the circuit had to be tuned for the exact motor to be used, and worked well enough to say that it worked, but not universally well. If the tuning was off in one direction, the load regulation was not good. If it was off in the other direction, the motor would have no speed regulation at all; it would just go as fast as it could.
If I remember correctly, the Basic Stamp has a PWM output that can chop a supply fast enough to make a DC motor run okay at a programmed fraction of its maximum speed. The actual speed developed would still depend on the load. No way is a Basic Stamp fast enough to close the loop and provide constant speed regardless of load, even if you had a way to measure applied load or actual speed.
Mike Halloran
Pembroke Pines, FL, USA