How does a brushed motor generate a magnetic field

So how does a brushed motor generate the rotating magnetic field required to rotate an armature without the need for an external regulator? It is the motor that works in itself. The motor housing contains a pair of brushes 180° apart that direct the current applied to the armature coil through two commutator contacts (metal plates). Each metal plate covers about 180° of an armature. As the motor rotates, the current loop (winding) between the power supply, brushes, commutator metal plate and two motor coils automatically changes every half turn.

The armature's magnetic field interacts with the rotor's magnetic field, and the rotor's magnetic field can be generated by the motor body's fixed coil or permanent magnet. As the rotor rotates, the direction of the magnetic field also reverses, the direction of the magnetic field generated by the coil is continuously switched and the motor rotates as it is attracted/repelled by the magnetic field generated by the external coil. or permanent magnets. Increase.

Note that the use of permanent magnets has historically been limited to small motors such as toys, because the magnets are not strong enough for the modest size and weight. However, the development of high-strength permanent magnets using rare earth materials has changed this situation, and PM-based BDC motors are suitable for large motors even in the small horsepower range. The PM method is more efficient because the external excitation coil does not require a power source, but it reduces the freedom of the system to control the operation of the motor. Whether it's a PM BDC motor or a field coil design, there are trade-offs between size, cost, weight, control needs, and more.