A permanent magnet rotor for an electronically commutated motor (ECM) has a core, a plurality of magnetizable elements spaced around the core, and a thin-walled retaining shell which has been stretched around the core and magnetizable elements to hold the elements in position. The rotor is made by an...http://www.google.ca/patents/US5040286?utm_source=gb-gplus-sharePatent US5040286 - Method for making permanent magnet rotor
