A stepper motor is a unique type of DC motor that rotates in fixed steps of a certain number of degrees.
Step size can range from 0.9 to 90°.
consists of a rotor and stator.
In this case, the rotor is a permanent magnet
current can only be directed through the coils of a Unipolar Motor in one direction
Unipolar Motors can only power individual phases at fixed polarities.
Wiring
Unipolar Stepper motors are manufactured with a central tap that connects back to the power source, essentially splitting each coil into two smaller coils that can be powered independently.
Bipolar Stepper Motors do not feature a central tap for dividing their solenoid coils - this makes their internal wiring slightly less complex than that of a Unipolar Motor.
For this reason, smaller Motors such as NEMA 14 Stepper Motors are more commonly available in a Bipolar configuration due to their reduced size.
Unipolar motors have their own distinct advantages and disadvantages, dependent on their application.
Unipolar Stepper Motors use tapped coils, of which each side can be independently magnetized. Because the current running through each coil will be running in a different direction dependent on which side of the coil is magnetised, the polarity of each phase can be reversed without reversing the current of the entire circuit. However, because only half of each coil is magnetised, Unipolar Stepper Motors suffer from reduced magnetic force, and thus reduced torque. Unipolar Motors are simpler to install and operate than Bipolar Stepper Motors, because their circuitry does not require the use of H-bridges.