Stepper Motor Windings and Winding Configurations

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A stepper IC controller, a device which can include commutation logic, an inverter, and a power supply on its chip, is often what is used to control a stepper motor. The current is usually switched with a stepper motor driver IC. These motors allow fairly exact motion and are appropriate for a great many applications. However, how the current supplied by the driver will work with the stepper is dependent upon the winding configuration.

How a Stepper Motor Works with a Winding Configuration

A stepper motor is designed to move in small increments, making it effective for precise work. The stepper can spin at high speeds, but the right motor can also stop at the exact degree angle you want it to. The way this works is heavily involved with how the motor windings are configured. Essentially, the current is passed through one winding, then the other, then back through the first with the opposite polarity and then back through the second with opposite polarity. This process continues as long as current is passed through the motor, and the result is continuous rotation. If you reverse a winding, the direction of the motor rotation will reverse.

About Stepper Motors and Stepper Motor Windings

A stepper motor usually has four, six, or eight wires with the appropriate number of independent windings. A four lead wire motor is run by a bipolar driver, while the six or eight wire motor can be run by unipolar or bipolar drivers.

The effect of the unipolar or bipolar driver on the stepper motor is largely manifested in the motor windings. With a unipolar driver, as the name would imply, the current can only be sent through the windings in one direction. This means less flexibility in how you can use the driver, but it offers an advantage when it comes to performance at high speeds. In contrast, the bipolar driver can send current through the windings both ways. This means more ways to connect stepper motors to such a driver, but creates a drop in high speed performance compared to the unipolar driver.

Why is the unipolar winding setup more effective at high speeds? The reason is that only half of the winding coils are used at a time. This reduces inductance, and it is inductance that resists changes in the flow of current at high speeds. However, at lower speeds, you will get less torque from this configuration, so you should use unipolar winding configurations specifically for motors that will be run at high speeds most or all of the time. On the other hand, in the bipolar winding configuration, the full coil is used. This produces more torque at lower speeds, but also causes much more inductance than the motor would experience in the unipolar configuration. This type of setup is much more effective when you have one or multiple motors that will be operating primarily at low to moderate speeds.

To improve higher speed motor performance with a bipolar winding configuration, you can create a half coil winding configuration with a bipolar driver for a six or eight lead wire motor. This will reduce inductance and improve high speed performance. Another option for keeping the inductance down at high speeds is to create a bipolar parallel winding configuration with an eight lead wire motor. In this configuration, you can make use of the entire winding without seeing a commensurate increase in inductance. The main downside to this type of configuration is that you need an increased amount of current relative to a similar motor run with unipolar winding configuration to get the result you are looking for. Below is a basic winding diagram and switching sequence to give you a visual idea of stepper motor windings.

Winding Diagram

Unipolar

Uni Polar Stepper Motor Windings Diagram

Bipolar

Bi Polar Stepper Motor Windings Diagram

Switching Sequence

Uipolar

  Dual
CW Rotation 
 
step
A -COM
B
1 - - 0 0 +
2 0 - - 0 +
3 0 0 - - +
4 - 0 0 - +
  CW Rotation Facing Mounting End

Bipolar

  Dual
CW Rotation 
 
step
1 + + - -
2 - + + -
3 - - + +
4 + - - +
  CW Rotation Facing Mounting End

It should be apparent that the configuration of a stepper motor has applications not only for major industrial projects, but for smaller projects as well. Here are some fun and interesting uses for a stepper, many of which are low speed applications that can benefit from the bipolar winding configuration.

Robot: If you’ve ever considered building your own robot, pick up some stepper motors. You can use them to create a simple mechanism that can walk, change direction, and pick things up. You can power robot wheels with a motor that generates about 5-10 volts. Keep in mind that you’ll want to keep the robot as light as possible, and figure on twice as much torque as you expect you will need.

Automatic Fish Feeder: Take the hassle out of caring for fish by integrating a stepper motor into a device that feeds your fish on your command. Not only will this allow you to go on vacation without having strangers in your home to take care of your fish, it’s a cool gadget that can impress friends and serve as a fun conversation piece.

Camera Panning: Having a camera in a room for security doesn’t do you that much good if it’s only fixed on a single point. This is an area where the right stepper motor can really come in handy. The rotary action and precise angles of a stepper motor are ideal for operating a camera panning system to capture all the action that is happening in a given room.

Turntable: If you’re a disc jockey or a vinyl record enthusiast, consider building your own turntable. A stepper motor can provide the rotating action you need to get your turntable moving.

You clearly don’t need to understand all of the inner workings of a stepper motor or stepper motor windings in order to use and benefit from this type of motor. Knowing these inner workings, however, can help you get a better understanding of what kind of motor you will need, whether or not a stepper motor is the best bet for your application, and what you can do with this kind of motor to use it most effectively.