1) Structure
     A DC motor consists of a stator and a rotor with a certain air gap in between. The main feature of its construction is an armature with a commutator. The stator of the DC motor is composed of the frame, the main magnetic pole, the commutation magnetic pole, the front and rear covers and the brush holder. The main magnetic pole is the main component that generates the air gap magnetic field of the DC motor, and is composed of a permanent magnet or a laminated core with a DC excitation winding. The rotor of the DC motor is composed of the armature, the commutator (also known as the commutator) and the rotating shaft. The armature consists of two parts, the armature core and the armature winding. The armature core is formed by stacking silicon steel sheets, and the tooth slots are evenly distributed on its outer circumference, and the armature windings are embedded in these slots. The commutator is a mechanical rectifying component. After the commutator segments are stacked into a cylindrical shape, they are formed as a whole with metal clips or plastics. The commutator segments are insulated from each other. The quality of the commutator has a great influence on the operational reliability.
2) The principle of reversible operation
In principle, a DC motor can run both as a motor and as a generator, which is called the reversible principle in motor theory. When the prime mover drives the armature winding to rotate between the main magnetic poles N and S, an electromotive force is induced on the armature winding, which is rectified to DC by the brush and commutator device, and then directed to the external load (or power grid) to supply power to the outside world. , the motor operates as a DC generator at this time. If an external DC power supply is used to lead the DC current to the armature winding through the brush commutator device, the current interacts with the magnetic field generated by the main magnetic pole N.S. to generate torque, which drives the rotor to work with the mechanical load connected to it. , the motor operates as a DC motor at this time.
3) Classification
According to the results, it is mainly divided into DC motors and DC generators.
According to the type, it is mainly divided into DC brush motor and DC brushless motor.
The excitation mode of the DC motor refers to the problem of how to supply power to the excitation winding, generate the excitation electromotive force and establish the main magnetic field. According to the different excitation methods, DC motors can be divided into the following types.
4) Excitation method
 The excitation mode of the DC motor refers to the problem of how to supply power to the excitation winding, generate the excitation electromotive force and establish the main magnetic field. According to the different excitation methods, DC motors can be divided into the following types.
1. Separately excited DC motor The field winding is not connected to the armature winding, and the DC motor powered by other DC power sources to the field winding is called a separately excited DC motor.
2. The excitation winding of the shunt DC motor is connected in parallel with the armature winding. As a shunt generator, the terminal voltage from the motor itself supplies power to the excitation winding; as a shunt motor, the excitation winding is connected to the power supply. The pivots share the same power supply, which is the same as the separately excited DC motor in terms of performance.
3. Series excitation DC motor The excitation winding of the series excitation DC motor is connected in series with the armature winding, and then connected to the DC power supply. The excitation current of this type of DC motor is the armature current.