There are basically two principles that govern a DC motor.
- How to repel poles of a magnet and tighten them differently. We have all played with magnets and are familiar with this simple observation.
- Magnetic effect of the current.
A DC motor has two magnetic fields, one of which is generated by the field or stator. It can be a permanent magnet or an electromagnet. Typically, smaller DC motors use permanent magnets.
The second magnetic field is generated by the rotor / armature / many other names. This is the rotating part. It is always of the electromagnetic type and consists of an insulated wire around a soft iron core.
When current flows through the armature, it behaves like an electromagnet and due to the magnetic field of the stator, a force is exerted on the armature. Now the situation is quite similar to two magnets that are close together – they either repel each other or attract each other. The anchor is constructed so that one of its sides is attracted and the other is pushed off and rotates as a result.
Such an armature can only make half a turn, since the sides of the armature are reversed and thus the magnetic forces acting on them. To continue the rotation, we have to reverse the current direction after every half rotation so that a split ring is used to reverse the current.