What is the difference between - bipolar and uni polar stepper motor?

Answer 1

Unipolar Stepper Motors

The unipolar stepper motor operates with one winding with a center tap per phase. Each section of the winding is switched on for each direction of the magnetic field. Each winding is made relatively simple with the commutation circuit, this is done since the arrangement has a magnetic pole which can be reversed without switching the direction of the current. In most cases, given a phase, the common center tap for each winding is the following; three leads per phase and six leads for a regular two phase stepper motor. You will usually see that both these phases are often joined internally, this makes the stepper motor only have five leads. Often a stepper motor controller will be used to activate the drive transistors in the proper order. Since it is quite easy to operate these stepper motors, they are often very popular among hobbyists and are usually the cheapest way to get precise angular movements.

Bipolar Stepper Motors

With bipolar stepper motors there is only a single winding per phase. The driving circuit needs to be more complicated to reverse the magnetic pole, this is done to reverse the current in the winding. This is done with a H-bridge arrangement, however there are several driver chips that can be purchased to make this a more simple task. Unlike the unipolar stepper motor, the bipolar stepper motor has two leads per phase, neither of which are common. Static friction effects do happen with a H-bridge with certain drive topologies, however this can be reduced with dithering the stepper motor signal at a higher frequency.

Answer 2

The main difference between bipolar and unipolar stepper motors lies in their coil configuration. Bipolar stepper motors have two separate coil windings per phase, allowing current reversal in the coils, while unipolar stepper motors have center-tapped coils which can be energized in one direction only. This means that bipolar motors have stronger torque but require more complex control circuits, while unipolar motors are easier to control but have lower torque output.