A stepper motor is a motor that rotates in discrete steps. Each step of the movement is precise and repeatable. Therefore, the position of the motor can be precisely controlled without any feedback mechanism, provided that the motor is sized to the application. This type of control does not require expensive sensing and feedback devices, such as optical encoders, and simply tracks the input stepper pulses to know the position. The position is known simply by tracking the incoming stepping pulses. This is one of the most versatile forms of positioning system. They are often controlled digitally as part of an open-loop system and are simpler and more robust than closed-loop servo systems.

Energising the coil winding produces an electromagnetic field with north and south poles. The magnetic field generated by the winding The magnetic field generated by the winding will align the magnetised rotor with the magnetic field, as the different poles attract each other.

The direction of the magnetic field can be altered to create the rotation of the rotor.

The diagram above shows a common 'two-phase pass' stepping where both phases are always energised. In this stepping mechanism, the rotor is balanced between the two poles. This method of stepping gives 41.4% more torque than 'single phase pass' stepping, but requires twice the input power

Advantages and disadvantages of stepper motors