An electric motor assembly with moving rotor segments to reduce a back electromotive force

An electric motor assembly includes a rotor hub and a rotor which is supported on the rotor hub. The rotor hub includes first and second hub portions and the rotor includes first and second annular rotor segments which are supported for rotation on the respective first and second hub sections. Each of the rotor segments includes a respective set of magnets which are spaced from each other circumferentially around it. The rotor hub and the rotor segments are designed such that at least one of the rotor segments about the rotational axis relative to said other of the rotor segments moves as the rotor hub rotates. The movement of the at least one of the rotor segments takes place by an amount which increases as the rotational speed of the rotor hub increases, to reduce a counter electromotive force. The movement can take place due to the centrifugal force which increases as the speed increases, without a control system is needed to effect the movement.