Electric Motor

An electric motor comprising:

• a stator having a plurality of magnetic poles;
• and
• a rotor rotatably mounted to the stator, the rotor comprising:
• a shaft;
• a commutator fixed to the shaft;
• a rotor core comprising a stack of laminations fixed to the shaft and located adjacent to the commutator;
• and
• rotor windings wound on the rotor core and electrically connected to the commutator,
• wherein each lamination comprises:
• an inner ring having a hole for fixing the shaft;
• an outer ring radially spaced from the inner ring;
• a plurality of teeth extending outwardly from the outer ring;
• and
• a number of ribs connecting the inner ring to the outer ring, each rib having a width w measured in a circumferential direction of the lamination;
• wherein the number of ribs is n, the width w and the number n satisfy the formula:
• 0.75≦n×w264, where the width w of each rib is measured in millimeters.