Variable Reluctance Motors
A variable reluctance motor is a stepping motor that does not use a permanent magnet. A step is achieved by the principle that the rotor will rotate to minimize the reluctance path of a magnetic circuit.
In the first step, pole 1 is magnetized north and pole 4 is magnetized south. In step 2, poles 2 and 5 are energized and poles 1 and 4 are turned off. The rotor rotates 60 degrees. In step 3, poles 3 and 6 are energized and so on.
Induction and squirrel cage motors have but a single turn electrical conductor in the rotor. They generally use copper bars or cast aluminum. The electric current is induced into the rotor from the stator field. These are AC motors and stepping is derived from the line frequency. There are many other specialized motors. However, the end result is still the same: to obtain rotary motion, you have to create a rotating magnetic field.