What is a Stepper Motor?

Stepper motors are electrical motors that are driven by digital pulses rather than a continuously applied voltage.  They are perfectly suited for accurate positioning of CNC machines and 3D Printers.

There are 2 types of popular Stepper Motors: Bipolar and Unipolar Motors.

uni-polar-stepper-motor-windingsUnipolar Steppers are more readily available and for cost reasons, more popular with hobbyists.  The control circuit for a Bipolar Stepper requires 8 power transistors (2 full H-Bridges) and 8 control lines from a micro controller.  We can do the same with only 4 transistors using a Unipolar Stepper.  Bipolar Steppers however supply more torque for same motor size.  You can identify Steppers by counting the number of wires or connections on the motor.

Unipolar steppers have 5 or 6 connections. If you count only 4 connections then the stepper is a Bipolar motor and is not suitable for our Stepper Driver . The most popular Unipolar motors typically turn 1.8 degrees per step, or 200 steps per revolution, others turn 7.5 degrees per step for 48 steps per revolution. When these motors are stepped in half step mode, the steps per revolution will double.

StepperMotor

An important thing to consider when buying a Stepper is it’s Voltage Rating.  Consider a stepper rated at 12V and another at 3V and both having a 30W power rating.  Even though they consume the same power, they do not perform equally.  The 3V Stepper will perform much better at high speeds than the 12V Stepper.  The reason is that the 12V stepper has more windings per coil and therefore a much higher inductance.  Since the current in the 12V Stepper at higher step frequencies will be lower, the torque available at high speeds will be considerably less than the 3V Stepper.