Pull-out torque : The maximum torque which can be applied to a motor, running at a given stepping rate, without losing synchronism. Reversing the excitation sequence will cause a clockwise rotation of the rotor. If the stator windings are excited in the sequence 1, 2, 3, 4 the rotor will move in consecutive 15° steps in the anti-clockwise direction. Activation of the phase 2 winding on its own would cause the rotor to rotate a further 15° in the anti-clockwise direction to align the adjacent pair of diametrically opposite rotor teeth. The next adjacent set of rotor teeth in the clockwise direction are then 15° out of step with those of the stator. If phase 1 of the stator is activated alone then two diametrically opposite rotor teeth align themselves with the phase 1 teeth of the stator. The most popular step angle is 1.8°.įigure 2.57. The step angle depends on the method of construction and is generally in the range 0.9-5°. The rotor consists of a cylindrical magnet which is axially magnetized. Typically, the stator has eight salient poles which are energized by a two-phase winding. Hybrid: The hybrid stepper motor is a combination of the previous two types. PM stepper motors give a large step angle, ranging from 45° to 120°. Permanent magnet: The rotor used in the PM-type stepper motor consists of a circular permanent magnet mounted onto the shaft. This type of stepper motor provides small to medium-sized step angles and is capable of operation at high stepping rates. The number of teeth on the rotor and stator, together with the winding configuration and excitation, determines the step angle. Variable reluctance: This type of stepper motor has a soft iron multi-toothed rotor with a wound stator. There are three basic types of stepper motor: 1.