A brushless DC motor is constructed with photosensitive device for detecting rotor shaft position. Arcuate permanent magnets on the rotor provide a DC flux field while distributed stationary armature windings, each spanning a fixed number of slots in the armature assembly, provide mutually perpendicular...http://www.google.fr/patents/US4169990?utm_source=gb-gplus-shareBrevet US4169990 - Electronically commutated motor
