Rotor
Rotor is the rotating electromagnetic part of a motor, mounted on or connected to the output shaft and separated from the stator by an air gap.
What the term covers
The rotor converts the interaction of magnetic fields into shaft torque. Its construction depends on motor type: it may carry permanent magnets, a conductive induction cage, electrical field windings, shaped flux barriers, or salient iron poles. These are not interchangeable labels for the same rotor.
Why rotor design matters
Rotor diameter, length, pole count, materials, and magnetic geometry influence torque, speed range, loss, and control. At high speed, laminations, magnets, bridges, sleeves, end rings, and joints must withstand centrifugal stress. Balance, bearing support, thermal expansion, and manufacturing tolerances must also keep the rotor centered inside a narrow air gap.
A rotor is not simply a flywheel. It is part of the motor's magnetic circuit, and its field or saliency determines how torque is produced. In an induction motor, rotor current is induced in the cage; in a synchronous motor, the rotor follows the stator field without induction-motor slip.
For detailed construction and topology comparisons, see EV Motor Construction and Windings.