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Stepper Motor Types

There are a many types and variations of stepper types, some of which require very specialized drivers. For our purposes, this guide will focus on stepper motors that can be driven with commonly available drivers.

How To Pick The Right Stepper Motor For The Job And How To Wire It
How To Pick The Right Stepper Motor For The Job And How To Wire It (A Stepper Motor fitted to a 4″ Precision Myford Lathe; credit: Tudor Barker via Flickr)

Step mottors driven with commonly available drivers are: Permanent Magnet or Hybrid steppers, either 2-phase bipolar, or 4-phase unipolar.


Motor Size

One of the first things to consider is the work that the motor has to do. As you might expect, larger motors are capable of delivering more power. Stepper motors come in sizes ranging from smaller than a peanut to big NEMA 57 monsters.

Most motors have torque ratings. This is what you need to look at to decide if the motor has the strength to do what you want.

NEMA 17 is a common size used in 3D printers and smaller CNC mills. Smaller motors find applications in many robotic and animatronic applications. The larger NEMA frames are common in CNC machines and industrial applications.

IMPORTANT! The NEMA numbers define standard faceplate dimensions for mounting the motor. They do not define the other characteristics of a motor. Two different NEMA 17 motors may have entirely different electrical or mechanical specifications and are not necessarily interchangeable.


Step Count

The next thing to consider is the positioning resolution you require. The number of steps per revolution ranges from 4 to 400. Commonly available step counts are 24, 48 and 200.

Resolution is often expressed as degrees per step. A 1.8° motor is the same as a 200 step/revolution motor.

The trade-off for high resolution is speed and torque. High step count motors top-out at lower RPMs than similar size. And the higher step-rates needed to turn these motors results in lower torque than a similar size low-step-count motor at similar speeds.

Gearing

Another way to achieve high positioning resolution is with gearing. A 32:1 gear-train applied to the output of an 8-steps/revolution motor will result in a 512 step motor.

A gear train will also increase the torque of the motor. Some tiny geared steppers are capable of impressive torque. But the tradeoff of course is speed. Geared stepper motors are generally limited to low RPM applications.

Title:All About Stepper Motors – Bill Earl; Adafruit Industries
Format:PDF
Size:2.0 MB
Pages:28
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How To Pick The Right Stepper Motor For The Job And What You Need To Know
How To Pick The Right Stepper Motor For The Job And What You Need To Know

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