Electric motors
Electric motors come in all shapes and sizes. For the scale of project that we will be working on in this modules, however, there are only a few types that will be relevant. This section provides some information about them.
All electric motors work on the same basic principles, the main one of which is that a conductor (wire) which is placed in a magnetic field will experience a lateral force when current flows through it as illustrated in Figure 1. The direction of the force experienced by the conductor depends on the direction of the magnetic field and the direction of the current. In the figure, the magnetic field does not change. The conductor, however, passes though the magnetic field in one direction and then loops back again. The two halves of the wire loop therefore experience forces in opposite directions and this causes the motor to turn.
Figure 1: Schematic representation of a simple DC motor showing the interaction between the electrical current and the magnetic field by Lookang many thanks to Fu-Kwun Hwang and author of Easy Java Simulation = Francisco Esquembre (Own work) CC BY-SA 3.0, via Wikimedia Commons
The motor in Figure 1 is a brushed DC motor. In order to keep the motor turning in the same directions, the current in the wire needs to be reversed every 180° - this is the job of the commutator shown in cyan. The electrical connection with the commutator is made using steel brushes which slide along its surface as it turns.
Other types of electric motor use different strategies for generating a magnetic field and maintaining the flow of current in the required direction. At base though, they all employ the same basic principle.
Electric motors