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 amde by an...http://www.google.ca/patents/US5144735?utm_source=gb-gplus-sharePatent US5144735 - Apparatus for assembling a permanent magnet rotor
