Bipolar permanent magnet and hybrid motors are constructed with a mechanism similar to that used in uni polar motor, except that the two windings are wired without center taps in the Figure 2. The motor itself is simpler, but the drive circuitry needed to reverse the polarity of each pair of motor poles is more complex.
Stepper motors come in a wide range of angular resolutions. The coarsest motors typically turn 90 degrees per step, whereas high resolution permanent-magnet motors can commonly handle 1.8 or even 0.72 degrees per step. With the appropriate controller, most permanent magnet and hybrid motors can be run in half steps, and some controllers can handle smaller fractional steps or micro steps. For permanent magnet and variable-reluctance stepper motors, when one winding of the motor is energized, the rotor (under no load) snaps to a fixed angle. It holds that angle until the torque exceeds the holding torque of the motor, at which point the rotor turns, trying to hold at each successive equilibrium point.
