Patent ID: 7732962

Claim:
A small DC motor, comprising: a motor frame comprising a cylindrical portion and an end plate portion, the cylindrical portion having a constant thickness and having a cross section in a shape that comprises four sides and connecting portions, each of the connecting portions connecting adjacent two of the four sides and being located inward from a corresponding corner in a quadrangle comprising the four sides; field magnets, each being positioned adjacent to each of the connecting portions, having an arc-shaped surface on an inside thereof and having a cross section in an inside portion that has an arc-shape and in an outside portion that has a same curvature as an inside surface of the connecting portions, and an armature assembly comprising an armature winding and a shaft and being disposed rotatably within the motor frame, wherein the field magnets are provided so as to be spaced apart from each other, wherein the small DC motor comprises an air gap between each of the four sides and a radially outermost surface of the armature assembly, wherein a radius from the center of the shaft to an inside surface of the motor frame is substantially same as a radius from the center of the shaft to the arc-shape surface of the inside portion of the field magnets, and wherein the air gap is set in a range of 0.1 mm to 0.5 mm.