Dc Motor Features and Roles

Describe the main features of a DC electric motor and the role of each feature

Part | Description | Role | Magnet(s) | Either permanent or electromagnetic. Induce a magnetic field and fit around the armature. | The magnets supply the magnetic field which interacts with the current in the armature to produce the motor effect. | Armature | The armature consists of a cylinder of laminated iron mounted on an axle. Often there are longitudinal grooves into which the coils are wound. | The armature carries the rotor coils. The armature is the part of a DC motor that rotates and provides energy at the end of the shaft. It is basically an electromagnet | Rotor coil(s) | There may be only one, in a very simple motor, or several coils, usually of several turns of insulated wire, wound onto the armature. The ends of the coils are connected to bars on the commutator. | The coils provide torque, as the current passing through the coils interacts with the magnetic field. As the coils are mounted firmly on the rotor, any torque acting on the coils is transferred to the rotor and thence to the axle. | Split-ring / commutator | The commutator is a broad ring of metal mounted on the axle at one end of the armature, and cut into an even number of separate bars (two in a simple motor). Each opposite pair of bars is connected to one coil. | The commutator provides points of contact between the rotor coils and the external electric circuit. It serves to reverse the direction of current flow in each coil every half-revolution of the motor. This ensures that the torque on each coil is always in the same direction. | Brushes | Compressed carbon blocks, connected to the external circuit, mounted on opposite sides of the commutator and spring-loaded to make close contact with the commutator bars. | The brushes are the fixed position electrical contacts between the external circuit and the rotor coils. Their position brings them into contact with both ends of each coil