Spindle motor

摘要

A spindle motor comprises a rotational member supported by bearings for rotation about a rotational axis, a rotational body and a motor rotor mounted on the rotational member for rotation therewith, and a motor stator mounted around the motor rotor. The rotational body has an outer diameter determined so that a windage loss of the rotational body is proportional to the third power of a peripheral velocity of the rotational body and an air gap diameter of the bearings and the diameter of the motor stator are determined so that the air loss of each of the bearings and the motor rotor is proportional to the square of the peripheral velocity of each of the bearings and the motor rotor at a range of constant speed of rotation of the rotational member.