Seems to me that gear motors plus a shaft encoder could produce a much higher slew rate than stepping motors driving screws. The question that I have is whether a PIC or Arduino (Atmel or similar low-speed processor e.g. msp430) could keep up with the optical interruption rate necessary for high resolution? Has anybody tried that?
The nice thing about stepping motors is that if you stay within their torque limits, you don't need any positional feedback other than a zero point. The bad thing is that you can't drive them beyond a certain speed because their torque flatlines.
