A motor includes a rotor including a shaft arranged along a central axis extending in one direction; and a stator arranged radially outside of the rotor. The stator includes a stator core including an annular core back portion arranged to surround the rotor, and a plurality of tooth portions arranged to extend radially inward from the core back portion; and coils each of which is wound around a separate one of the tooth portions. The tooth portions are arranged side by side along a circumferential direction. An inner edge of the core back portion is in the shape of a polygon when viewed along an axial direction. The inner edge includes rounded corners each of which is arranged between portions of the inner edge to which circumferentially adjacent ones of the tooth portions are joined. When D1 denotes an inside diameter of the stator core, D2 denotes a minimum outside diameter of the stator core, and N denotes the number of tooth portions, the ratio of D1 to D2 is greater than 0.65, and R of each corner of the inner edge is in the range of D1/N to D2/N inclusive.

A step motor includes a plurality of stator cores. Each of the stator cores have a coil unit coiled therearound. The step motor includes a rotor that includes a rotation shaft and a plurality of permanent magnets and is configured to rotate by magnetic interaction between the stator cores and the permanent magnets. The step motor also includes a plurality of conducting parts on one cross-sectional surface of the rotor. The step motor further includes a printed circuit board (PCB) including electric elements that are arranged at certain positions and are disposed to face the conducting parts. The conducting parts and the electric elements are configured to electrically or magnetically interact as the rotor rotates to change electrical signals generated by the electric elements.

A step motor includes a plurality of stator cores. Each of the stator cores have a coil unit coiled therearound. The step motor includes a rotor that includes a rotation shaft and a plurality of permanent magnets and is configured to rotate by magnetic interaction between the stator cores and the permanent magnets. The step motor also includes a plurality of conducting parts on one cross-sectional surface of the rotor. The step motor further includes a printed circuit board (PCB) including electric elements that are arranged at certain positions and are disposed to face the conducting parts. The conducting parts and the electric elements are configured to electrically or magnetically interact as the rotor rotates to change electrical signals generated by the electric elements.