Thread: Unipolar vs Bipolar driver

It basically has to do with the way the motor is driven.

Unipolar motors

A unipolar stepper motor has two windings per phase, one for each direction of magnetic field. Since in this arrangement a magnetic pole can be reversed without switching the direction of current, the commutation circuit can be made very simple (eg. a single transistor) for each winding. Typically, given a phase, one end of each winding is made common: giving three leads per phase and six leads for a typical two phase motor. Often, these two phase commons are internally joined, so the motor has only five leads.


Bipolar motor

Bipolar motors have a single winding per phase. The current in a winding needs to be reversed in order to reverse a magnetic pole, so the driving circuit must be more complicated, typically with an H-bridge arrangement. There are two leads per phase, none are common.
Static friction effects using an H-bridge have been observed with certain drive topologies


Because windings are better utilized, they are more powerful than a unipolar motor of the same weight.


8-lead stepper

An 8 lead stepper is wound like a unipolar stepper, but the leads are not joined to common internally to the motor. This kind of motor can be wired in several configurations:

• Unipolar.
• Bipolar with series windings. This gives higher inductance but lower current per winding.
• Bipolar with parallel windings. This requires higher current but can perform better as the winding inductance is reduced.
• Bipolar with a single winding per phase. This method will run the motor on only half the available windings, which will reduce the available low speed torque but require less current.

Here is a really good link which explains a lot more than what i posted

Stepper motor - Wikipedia, the free encyclopedia

/Michael

Hmm, thanks for replying Mike, was thinking it may be a silly question due to lack of replies

Breaking that down to super layman interpretation - so a unipolar motor has two wires wrapped around what ever it is called that they are wrapped around, to make the motor go in one direction it sends a current down one wire, to make it turn the other way it send a current the opposite direction down the other wire. This means that the current turning the motor is only running through wire that is covering half the surface it is running over.

A bipolar motor however has a single wire running the entire length over whatever it is called that it is wrapped around. To run it in one direction the current runs one way along the wire, to run it the other direction the current is reversed along the same length of wire. As the wire that the current is running through is covering the entire surface (as opposed to half the surface in a unipolar motor) it therefore has more effect on whatever it is doing and is therefore more powerful. The wiring to do this is more complicated than in a unipolar motor however.

Taking a stab in the dark would it then be correct to say then that since the current has to reverse and travel further in a bipolar motor that they will be slower than a unipolar motor of same size?

or ??


And what is a "phase" and a "lead"??