Slotless Motor Design Procedure

The type of slotless winding is chosen first. Then the basic dimension parameters are set. The magnet material, stator, and hub steel materials are set. The flux density values in the stator back iron and rotor back iron are inspected and the dimensions adjusted so they are at acceptable values. The core loss at rated speed is also inspected and additional adjustments are made to the dimensions. Next the number of turns, the wire size, and the strands are adjusted so that the desired resistance and back emf are obtained. The slot fill factor is an important factor to be watched in this process. This procedure is repeated while changing parameters including materials until all desired objectives are obtained. The coil radial height or coil radial thickness becomes important in slotless motors, it is important to keep this parameter less than the space available for the coil in the radial direction.

Slotless motors supported at this time include-

1) Concentrated coils. These coils may be thought of as coils in a slotted motor with a span of 1 slot.

2) Distributed coils. These coils have a coil span of 180 electrical degrees and have overlaps. So the height of the coil in the radial direction requires some attention to fit inside the air gap.

3) F coil, which is propriety Portescap technology.