Stepper motors are those neat little motors that don’t just go round and round when you connect them, but go round in jerks, 7.5°, 10° or 15° at a time. This is technically called ‘cogging’. Inside, they have two sets of electromagnet coils that pull the magnetic rotor around by a small angle each time they are pulsed.
You can buy a stepper motor for less than $10 (£8), but don’t buy one straight away. You may find you can use one from an unused or broken printer or scanner. The printer in the picture below has three stepper motors. If you have a choice, choose the stepper motor that feels the most ‘notchy’, the one that clicks most positively into place as you rotate the shaft. (Cleaning and light oil may be needed for a stepper that has paper dust and ink toner on its bearings.)
Image credit: Neil Downie
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