Having watched a couple of videos on the Arduino running stepper motors, I take back what I said last time about not using software to control them. Although they do use additional hardware to drive the motor, the programs tell them when to take each step and how long to wait before taking another one. The delay determines the speed. These methods simply involve regular digital I/O pins to generate the pulses for the stepper motor.
A cursory look at my favorite auction site yields prices and varieties on a par with servo motors. Apparently they are often used with the mechanisms for 3D printers. Mounting brackets are generally more expensive than the stepper motors that they are meant to hold.
And so, stepper motors would seem to be a valid alternative to continuous rotation servos and may be more scalable (they can do some heavy lifting with the proper driving hardware). However, the driving hardware, though simple and available, adds to the overall cost.
