US Patent 7859164 Armature laminations

A DC motor, has a stator housing accommodating a permanent magnet stator; a rotor, rotatably mounted confronting the stator, the rotor having a shaft, a rotor core fitted to the shaft and having asymmetric laminations, a commutator fitted to the shaft adjacent one end of the rotor core, and windings wound about poles of the rotor core and terminated on the commutator; and brush gear comprising brushes in sliding contact with the commutator for transferring electrical power to the windings, wherein the cogging torque order for the motor is greater than twenty. Preferably, the cogging torque order is 28, 36 or 44.