Thanks MikMo...
So, I've figured that what I probably need are stepper motors, each with its own controller so I don't have to send insane amounts of control information directly to the motors.
Has anyone ever used something like this motor + controller combo?:
http://www.ebay.com.au/itm/Set-2-4-Phase-DC-Gear-Stepper-Motor-ULN2003-Driver-Board-Shield-/290682227578?pt=LH_DefaultDomain_15&hash=item43ae02cb7a
I'm guessing that this unit receives some kind of instructions from an Arduino over a 3 or 4-wire interface, such as "spin left for x turns"...??
Assuming it's powerful enough for my needs (I'll probably end up using some kind of gearing), does anyone know of a simple chip that could interface with the motor controllers in a way that MikMo described? Suppose my central Arduino sent out two bytes of info at a time: the first to select which motor to control, the second to give the motor controller an instruction like "spin right x turns" - all this chip has to do is listen for its unique ID in the first byte, then route the following byte of info through to its respective motor controller.
Hmmm.