In the middle motor, the coil is elongated, and it is wound around an iron core, which is mounted symmetrically about the shaft, with its (long) axis perpendicular to the shaft. In the motor at left, the coil is flat, and the windings are close to the shaft on either side. The simplest armature is a single coil, wound about an axis perpendicular to the motor shaft, with the windings symmetrical about the shaft, so that its magnetic field is perpendicular to the shaft. A pair of brushes, which touch the commutators, provides contact with the power supply. The rotor consists of a central axle on which is mounted the armature coils and, to provide electrical contact, the commutators, to which the ends of the armature coils are connected. This means of producing torque finds practical application in electric motors, which use this phenomenon to convert electrical energy to mechanical energy, and thus, to perform mechanical work.Ī permanent magnet motor is one in which a magnet, or pair of magnets, provides the static magnetic field in which the rotor rotates. Demonstration 68.48 - Torque on current-carrying loop, shows that if you place a coil in a magnetic field, oriented so that a current in it produces a magnetic field that is not parallel to that of the external magnetic field, the coil experiences a torque, which, if the coil is mounted so as to allow it, rotates the coil in whichever direction aligns its magnetic field with the external field. Several demonstrations in this chapter ( 68.30 - Electromagnet 68.34 - Cathode ray tube, coil 68.45 - Field of current-carrying coil, solenoid, toroid 68.46 - Magnetic fields of coils) show that, by running current through a coil, you can produce a magnetic field similar to that of a bar magnet. In the center and at right are two Saint Louis motors made by CENCO.

At left in the photograph is a home-made permanent magnet DC motor.

How to make a permanent magnet