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 ≈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