Patent ID: 7427817

Claim:
A small-sized motor having a polygonal outer shape in which four or more field magnets are attached to an inner surface of a motor casing made of metal, comprising: a tubular portion of the motor casing being formed into a polygonal tubular shape such that flat side portions equal in number to field poles, and curved corner portions equal in number to the field poles and each curved corner portion being located between the adjacent side portions are sequentially joined together, said each curved corner portion being curved along an arc whose center is an axis of rotation of the motor; a dimension C is defined as a vertical or horizontal dimension of the cross-section of the motor, and a dimension D is defined as a dimension of each of the flat side portions, a percentage of dimension D to dimension C is between 5% and 95%; and the field magnets each having a larger thickness at portions corresponding to the corner portions of the motor casing, and a smaller thickness gradually decreasing from the larger thickness portions toward circumferentially opposite ends, wherein the field magnets coincide in center position with the corresponding corner portions of the motor casing.