Editing Stepper motor (section)

==== Bipolar motors ====
[[File:A bipolar stepper motor used in DVD writers.jpg|thumb|A bipolar stepper motor used in [[Optical disc drive|DVD drives]] for moving the laser assembly.]]
Bipolar motors have a pair of single winding connections 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 (however there are several off-the-shelf driver chips available to make this a simple affair). There are two leads per phase, none is common.

A typical driving pattern for a two coil bipolar stepper motor would be: A+ B+ A− B−. I.e. drive coil A with positive current, then remove current from coil A; then drive coil B with positive current, then remove current from coil B; then drive coil A with negative current (flipping polarity by switching the wires e.g. with an H bridge), then remove current from coil A; then drive coil B with negative current (again flipping polarity same as coil A); the cycle is complete and begins anew.

Static friction effects using an H-bridge have been observed with certain drive topologies.<ref>See "Friction and the Dead Zone" by Douglas W Jones https://homepage.divms.uiowa.edu/~jones/step/physics.html#friction</ref>

Dithering the stepper signal at a higher frequency than the motor can respond to will reduce this "static friction" effect.
[[File:A bipolar stepper motor with a reduction gear mechanism.jpg|thumb|A bipolar stepper motor with gear reduction mechanism used in a [[Image scanner|flatbed scanner]].]]
Because windings are better utilized, they are more powerful than a unipolar motor of the same weight. This is due to the physical space occupied by the windings. A unipolar motor has twice the amount of wire in the same space, but only half used at any point in time, hence is 50% efficient (or approximately 70% of the torque output available). Though a bipolar stepper motor is more complicated to drive, the abundance of driver chips means this is much less difficult to achieve.

An 8-lead stepper is 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