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Stellaris® Stepper Motor Reference Design Kit Overview
10 November 4, 2009
Motor Technology
Introduction to Stepper Motors
Stepper motors are synchronous DC motors which rotate in precise increments as their coils are
energized. Stepper motors typically have step angles of 0.9°, 1.8°, 7.5°, or 15°. The motor in the
RDK has a step angle of 1.8° for a total of 200 steps per revolution. Figure 1-1 shows a detailed
photo of the NEMA23 stepper motor included in the RDK.
There are several different families of steppers motors, some with and some without permanent
magnets (PM). The most common type in industrial applications is known as a hybrid stepper
motor because it combines attributes from PM and non-PM motor construction.
Figure 1-1. Stepper Motor
The rotor on a hybrid stepper motor typically has 200 teeth made from a suitable magnetic
material and surrounding one or more powerful embedded magnets. As the stator phase is
energized, the opposing pole in the next rotor tooth is attracted, resulting in a single-step.
Note that the torque curve of stepper motors is far from linear (see Figure 1-2). For each step, the
motor develops peak torque when the rotor teeth are offset by one-quarter tooth pitch from the
opposing pole in the energized phase. Also, overall motor torque drops considerably as motor
speed increases. For this reason stepper motor torque is specified as the holding torque, or torque
with no angular motion.
Stator coils
Stator teeth
50 rotor teeth
on each pole
South pole
North pole
Double-stack motor has
2 sets of magnets
Front bearing
Shaft