Where to find stepper motors

Stepper motors can be found in almost any piece of electro-mechanical equipment. It can be pulled from old electronic equipment such as floppy drives, dot-matrix printers. Most of the stepper motors in Ritchie street is pulled from printers and the most common step angle you could find is 1.8deg and 7.5deg which is of permanent magnet type. Look for "unipolar" or "4-coil" or "4-phase" motor (they all mean the same thing) with 5 or 6 or 8 wires. Avoid "bipolar" motors because they require an entirely different control scheme. The require two phases to control them and have four wires.

Operating voltage of 12V is convenient for robotics projects. Look for motors with a coil current of 250mA or less (coil resistance of 48ohms or more for a 12V motor <-> V=IR). Higher currents do give higher torque, but will also drain your battery faster. Another key specification is the holding torque which is how much torque the motor can resist when energized.