Outer rotor¹⁾ or rotating stator²⁾, or moving stator³⁾ - a part of an electric motor or generator, which looks similarly to an ordinary stator, but is designed to rotate and performs the function of the rotor.

For instance, in an induction motor the stator envelopes the rotor, which revolves inside. No electrical connections are needed to the rotor, but they can be made conveniently to the stator, which does not move.

Inner stator (S) and outer rotor (R)^{4) USPTO, Public domain}

However, in some applications it is more advantageous to have the outer part rotating, and the inner part stationary. Such construction is used for instance for direct drive of conveyor belts. The outer part is designed to have the belt placed directly on it.

This concept is also used in some permanent magnet generators for wind turbines. The electrical windings and connections are made on the stationary inner part. The outer part is equipped with permanent magnets, whose rotation generates voltage in the stationary winding on the inner stator. The outer part also gives the possibility of mounting the turbine blades on it.

The difference between the two names is that “outer rotor” refers to the mechanical function of the part, whereas “rotating stator” to the appearance (the part is located outside and looks similarly to a stator in an ordinary machine).

Outer rotor

^{S. Zurek, E-Magnetica.pl, CC-BY-4.0}

Inner stator

^{S. Zurek, E-Magnetica.pl, CC-BY-4.0}

Inner stator

^{S. Zurek, E-Magnetica.pl, CC-BY-4.0}

Inner stator, with wave winding visible

^{S. Zurek, E-Magnetica.pl, CC-BY-4.0}

• Inner stator