Stepper Motor Tutorial: Learning the Basics

What is a Stepper Motor?

A stepper motor is a synchronous, brushless motor that runs on a pulsed current, where each pulse turns a rotor some fraction of a full rotation. Servo motors typically satisfy a wider range of applications, particularly when precision motion is needed, but stepper motors can be a useful alternative, depending on the application.

Stepper motors are rugged, economical and well-suited for digital drives and applications without close-loop feedback. They are typically used for spinning-disk hard drives, printers, robotics, CNC machine tools and more.

Stepper Motors 101: How Do They Work?

A stepper motor consists of a central rotor surrounded by a stator that contains a varying number of windings, depending on the model of stepper motor. To induce motion, these windings are energized, becoming electromagnets with a polarity determined by the direction of the current.

Typically, these directions include north poles and south poles. When a winding is energized, a rotor is forced to turn until a rotor’s north pole is positioned in proximity to a winding’s south pole, bringing torque down to zero. This constitutes one step.

For motion to continue, the first set of windings must be de-energized and another set energized. The result is another step.

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Types of Stepper Motors

There are several different types of stepper motors available today. However, the most common forms include the following:

• Two-phase permanent magnet (PM) stepper motor: this model has a rotor that contains a permanent magnet and a stator with four windings, creating a step angle of 90 degrees. PM stepper motors are an economical option, but provide low levels of torque.
• Variable-reluctance stepper motor: this model does not include a permanent magnet, and the number of rotor teeth differs from stator coils. Motion is created through varying widths in air gaps between the rotor and stator. Variable-reluctance stepper motors are a higher resolution alternative to PM stepper motors.
• Hybrid stepper motors: this model contains characteristics of both of the above stepper motors. It has a rotor that contains a permanent magnet, but the rotor teeth and stator coils are misaligned by half a tooth pitch with typically around 200 steps per revolution.

Stepper motors can perform a wide variety of functions, depending on the model and application. It's important to understand how stepper motors work, what their limitations are, and how this applies to your application before you invest in a stepper motor.