Actually (and I am replying to the OP, not my own message) you might be better off with a grunty servomotor. Some R/C servos are capable of very high torque and rapid and accurate positioning. In fact, since a servo is often used to give a 180 degree output range it might suit this project better to gear the output down (because such a large range is not required) and thereby increase the torque. That would keep the cost down too, and you wouldn't have to write your own PID controller for positioning.
A
