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Identifying Common Stepper Motor Types:

Stepper motor and brushless DC motors are commonly classified by the number of phases they have. Bipolar Steppers are 2 phase brushless motors and typically can be identified as having 4 leads or connections.

Bipolar Schematic Symbol


 Bipolar Physical Model

Unipolar Steppers are 4 phase brushless motors and typically can be identified as having 5 or 6 motor leads or connections.

Unipolar Schematic Symbol


Unipolar Physical Model

In the case of the 5 lead unipolar motor, the center pair of common wires are connected internally. A unipolar motor can be used as a bipolar motor by leaving the common leads unconnected This increases the step angle and also increase the torque and the current draw.

Additionally there are hybrid unipolar/bipolar motors known as universal stepper motors available that have 4 independent windings and 8 leads that can be used in both unipolar and bipolar configurations. By paralleling or connecting the windings in series the user can create either a unipolar or bipolar motor.

Universal Schematic Symbol


Identifying the characteristics of an unknown motor:

Fortunately stepper manufacturers almost always print the type, step angle, coil resistance, and coil voltage on the motors. When this information is not available then it can almost always be determined with the help of multimeter and some basic testing. The vast majority of the motor on the market are unipolar, bipolar, or a universal. Based on this assumption you can make a first guess at the motor type by counting the leads.

First count the number of motor leads.

2 Brush DC Motor - Not a Stepper
4 Bipolar Stepper
5 Unipolar Stepper - Common Center Tap
6 Unipolar Stepper
8 Universal

The final step is to use an ohm meter to determine connection of each of the leads and verify your initial motor type guess. A bipolar motor is the simplest, you verify which leads connect to each coil. Connect the motor to your controller to test it. If you have one of the coil's polarities backward then simply reverse the wiring of one coil. With a unipolar, the resistance V+ to common and V- to common should be equal and 1/2 the resistance between V+ and V-.

Copyright Wirz Electronics 1998