Describe the main features of a DC electric motor and the role of each feature - Electrical motors can be classified as either: o DC (direct current) motors: or o AC (alternating current) motors
- The commutator DC motor consists of: o An Armature (the rotor) o A magnetic field produced by permanent magnets or by electromagnets. It is equivalent to the stator o A commutator to reverse the direction of the current o Connecting brushes to take the current to and from the armature
- The armature is made up of a large number of coils (or turns) wrapped around an iron core that is free to rotate about a horizontal axis (hence the rotor). These coils are arranged at angles to each other. (To minimize the air gap between the armatures conductors and the stator, the conductors are often imbedded in slots cut longitudinally into the metal core.
- In its simplest form the field structure (stator) is made with permanent magnets (called field magnets), but also can be made from electromagnets (called field coils). The stator is approximately circular as this improves the smoothness of the torque.
- In its simplest form the split ring commutator consists of a copper cylinder divided in two electrically separated halves. Each half is connected to one side of the armature.
- Brushes are graphite pieces in their simplest form, which make contact with the commutator as t rotates. Springs ensure that the brushes are held firmly against the commutator.
- The coil can be considered as a magnetic dipole.
- When the plane of the rotating coil reaches horizontal, the brushes will break contact (nothing is lost, because when θ = 0 degrees then the torque will be 0 –the forces act inwards). The angular momentum of the coil carries it past the break point and the current then flows in the opposite direction, which reverses the magnetic dipole within the coil, and thus