The rotor or armature is the movable part on the shaft, which is placed in the bearing of the stator.
The rotor has also copper windings that can generate a force when the windings carry a current in a
magnetic field. For a continue force the current direction in the windings must react on the value of
the magnetic field. For direct current motors this phenomenon is called commutation. Consist the
rotor of permanent magnetic material then the stator windings must have carry current depending of
the rotor position.
Induction motors working according to the induction principle. The rotor consists of short-circuited
bars or windings. There is no commutation.
At last the rotor can consist only of magnet iron. The generation of force is according the reluctance
principle. The rotor iron follows a moving magnetic field.
Because the rotor has to guide the magnetic field from one side to the other side of the stator it is
nearly totally made of magnet iron. Exception of this construction are the so called air gap rotors and
permanent magnets rotors. The form of the rotors can be like a cylinder, a disk or like a cup. The cup
and disk forms are the air gap rotors, they have a low inertia. That is why those motors are very
capable for situations with high accelerations and decelerations (servo applications).
In case the armature moves from left to right it is called a linear actuator (lineator). The working
principle is the same as for rotational actuators, but the choice for linear movable actuators is much
greater. The reason is that there are so many different type of lineators and mostly custom made.
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