(also magnetic stepping motor), a synchronous motor in which current pulses supplied to stator windings are converted into discrete angular motions, or steps, of a rotor. A stepper motor may be either a salient-pole motor or a non-salient-pole motor. The field windings are on the stator, and the rotor has no winding. In a variable-reluctance stepper motor, the rotor is made of a soft magnetic material. In a permanent-magnet stepper motor, the rotor is made of a hard magnetic material.

Figure 1. Cross section of a stepper motor: (a) at the initial moment, (b) at the moment the next set of stator windings is energized, (c) upon rotation through an angle θ; (1) stator, (2) rotor, (3) field windings

The current pulses are supplied from a power source to the field windings in sequence through a commutator. As a result, the direction of the magnetic flux in the space between the stator poles changes in discrete steps (Figure 1), causing the rotor to rotate through a certain angle θ. Each such rotation of the rotor is called a step.

The magnitude of a step depends on the number of field windings and either on the number of rotor projections (for a variable-reluctance stepper motor) or on the number of salient poles (for a permanent-magnet stepper motor). The step is usually 1.5°–3° for variable-reluctance motors or 15° for permanent-magnet stepper motors. A permanent-magnet stepper motor makes it possible to obtain a relatively high torque and ensures that the rotor does not move when the windings are not energized.

Stepper motors are used in electric stepping drives.