So sieht so ein Motor von innen aus.

+12v dc, four-phase, unipolar, permanent magnet, 3.6° per step

In the KP4M4-001 Stepper motor, the permanent magnet lies North - South along the shaft. It is encased in two "stacks" each with 25 teeth round the rim. The teeth on the South stack are out of phase with the teeth on the North stack by half the gap between teeth.

http://www.doc.ic.ac.uk/~ih/doc/stepper/kp4m4/

Bild hier