A brushless ironless DC machine

A novel brushless DC machine which features an 'ironless' internal stator wound with a three phase slotless winding, and an external rotor comprising a drum of low-cost ceramic magnets, is described. A theoretical analysis of the machine's magnetic field is shown to produce phase voltages which are in close agreement with experimentally determined results so that the performance of the machine may be calculated by a simple computer model. Measured performance curves are shown to be in good agreement with such theoretical results and peak efficiencies of approximately=65% are observed for a 100 watt machine. The machine uses a simple single-ended electronic commutator to achieve a low-cost, low-noise variable speed drive suitable for a variety of applications.