PM motors, stepper motors and brushless DC motors A DC motor is
an electromechanical device that converts electrical energy into
mechanical rotational energy when energized by a constant
voltage (DC). Mechanically, it consists of a rotor and a stator,
and electrically of a field and an armature. In the very common
permanent magnet (PM) motor, the stator contains the permanent
magnet that provides a constant magnetomotive force and the pole
pieces, while the rotor is the armature, through which the motor
current flows. There is a complete magnetic circuit through
field and armature, with only short air gaps that allow the
armature to rotate. Current flowing in the armature experiences
a force in the magnetic field that causes the armature to
rotate. This force is proportional to the current and to the
strength of the magnetic field. When the armature rotates, an
electromotive force is induced in the armature windings that
would, acting alone, cause a current opposite in direction to
the current causing the arm