Editing Stepper motor (section)

==== Unipolar motors ====
A unipolar stepper motor has one winding with [[center tap]] per phase. Each section of windings is switched on for each direction of magnetic field. Since in this arrangement a magnetic pole can be reversed without switching the polarity of the common wire, the [[Commutator (electric)|commutation]] circuit can be simply a single switching transistor for each half winding. Typically, given a phase, the center tap of each winding is made common: 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.[[File:28BYJ-48 unipolar stepper motor with ULN2003 driver.jpg|thumb|The 28BYJ-48, accompanied by a [[ULN2003A|ULN2003]] driver, is one of the most popular stepper motors among hobbyists.]]

A [[microcontroller]] or stepper motor controller can be used to activate the drive [[transistor]]s in the right order, and this ease of operation makes unipolar motors popular with hobbyists; they are probably the cheapest way to get precise angular movements.
For the experimenter, the windings can be identified by touching the terminal wires together in PM motors. If the terminals of a coil are connected, the shaft becomes harder to turn. One way to distinguish the center tap (common wire) from a coil-end wire is by measuring the resistance. Resistance between common wire and coil-end wire is always half of the resistance between coil-end wires. This is because there is twice the length of coil between the ends and only half from center (common wire) to the end. A quick way to determine if the stepper motor is working is to short circuit every two pairs and try turning the shaft. Whenever a higher-than-normal resistance is felt, it indicates that the circuit to the particular winding is closed and that the phase is working.
[[File:Unipolar stepper motor with reduction gear mechanism.jpg|thumb|Stepper motors like this are often accompanied by a reduction gear mechanism to increase the output torque. The one shown here was used in a [[Image scanner|flatbed scanner]].]]