1. The principle of brushed motor

The brushed motor adopts mechanical commutation, the magnetic pole does not move, and the coil rotates. When the motor is working, the coil and the commutator rotate, but the magnetic steel and the carbon brush do not rotate. The alternating change of the current direction of the coil is accomplished by the commutator and brush that rotate with the motor.
In a brushed motor, the process is to arrange the two power input ends of each group of coils into a ring in turn, and separate them with insulating materials to form a cylinder-like thing, which is integrated with the motor shaft. Through two small columns (carbon brushes) made of carbon elements, under the action of spring pressure, from two specific fixed positions, press the two points on the upper coil power input ring cylinder to energize a group of coils.

As the motor rotates, different coils or different two poles of the same coil are energized at different times, so that the N-S poles of the magnetic field generated by the coils and the N-S poles of the closest permanent magnet stator have a suitable angle difference. Repel each other, generate force, and push the motor to rotate. The carbon electrode slides on the coil terminal like a brush on the surface of the object, so it is called a carbon "brush".

Sliding with each other will rub the carbon brushes and cause loss, and the carbon brushes need to be replaced regularly; the on-off between the carbon brushes and the coil terminals will alternate, sparks will occur, electromagnetic breakage will occur, and electronic equipment will be disturbed.

2. Working principle of brushless motor
The brushless motor adopts electronic commutation, the coil does not move, and the magnetic pole rotates. The brushless motor uses a set of electronic equipment to sense the position of the magnetic pole of the permanent magnet through the Hall element. According to this perception, the electronic circuit is used to switch the direction of the current in the coil in time to ensure that the magnetic force in the correct direction is generated to drive the motor. . Eliminates the disadvantages of brushed motors.
These circuits are the motor controllers. The controller of the brushless motor can also realize some functions that the brushed motor cannot, such as adjusting the power switching angle, braking the motor, making the motor reverse, locking the motor, and using the brake signal to stop the power supply to the motor. Now the electronic alarm lock of the battery car makes full use of these functions.
The brushless DC motor consists of a motor body and a driver, and is a typical mechatronic product. Because the brushless DC motor runs in a self-controlled manner, it will not add a starting winding to the rotor like a synchronous motor with heavy-load starting under variable frequency speed regulation, nor will it cause oscillation and loss of step when the load changes abruptly.

Three, the difference of speed regulation
In fact, the control of the two motors is voltage regulation, but because the brushless DC adopts electronic commutation, it can only be realized with digital control, while the brushed DC is commutated through carbon brushes, using thyristors, etc. Traditional analog circuits can be controlled, which is relatively simple.

1. The speed regulation process of the brushed motor is to adjust the voltage of the motor power supply. The adjusted voltage and current are converted through the commutator and the brush to change the strength of the magnetic field generated by the electrodes to achieve the purpose of changing the rotational speed. This process is called variable speed regulation.
2. The speed regulation process of the brushless motor is that the voltage of the power supply of the motor remains unchanged, the control signal of the ESC is changed, and the switching rate of the high-power MOS tube is changed by the microprocessor to realize the change of the speed. This process is called variable frequency speed regulation.

Fourth, the performance difference
1. The brushed motor has simple structure, long development time and mature technology
As early as the 19th century, when the motor was born, the practical motor produced was the brushless form, that is, the AC squirrel-cage asynchronous motor. This motor has been widely used after the generation of alternating current. However, asynchronous motors have many insurmountable defects, so that the development of motor technology is slow. In particular, the DC brushless motor has been unable to be put into commercial operation. With the rapid development of electronic technology, it has not been put into commercial operation until recent years, and it still belongs to the category of AC motor in essence.

Soon after the brushless motor was born, people invented the DC brush motor. Due to the simple structure of the DC brush motor, the production and processing are easy, the maintenance is convenient, and the control is easy; the DC motor also has fast response, large starting torque, and can provide rated torque from zero speed to rated speed. has been widely used.

2. The DC brush motor has fast response speed and large starting torque
The DC brush motor has fast starting response speed, large starting torque, stable speed change, almost no vibration from zero to maximum speed, and can drive a larger load when starting. The brushless motor has a large starting resistance (inductive reactance), so the power factor is small, the starting torque is relatively small, there is a humming sound when starting, accompanied by strong vibration, and the driving load is small when starting.

3. The DC brush motor runs smoothly, with good starting and braking effects
The brushed motor adjusts the speed through voltage regulation, so the starting and braking are stable, and the constant speed operation is also stable. Brushless motors are usually digital frequency conversion control, which first converts AC into DC, then DC into AC, and controls the speed through frequency changes, so the brushless motor runs unevenly during starting and braking, and the vibration is large, only when the speed is constant. will be stable.

4. High control precision of DC brush motor
The DC brush motor is usually used together with the reduction box and the decoder, so that the output power of the motor is larger, and the control accuracy is higher. The control accuracy can reach 0.01 mm, and the moving parts can be stopped almost anywhere. All precision machine tools are controlled by DC motors for precision. Because the brushless motor is not stable when starting and braking, the moving parts will stop to different positions each time, and the positioning pins or limiters must be used to stop at the desired position.

5. The DC brush motor has low cost of use and convenient maintenance. Due to the simple structure, low production cost, many manufacturers, and relatively mature technology, DC brushed motors are widely used, such as factories, processing machine tools, precision instruments, etc. If the motor fails, just replace the carbon brush. Carbon brushes only cost a few dollars, which is very cheap. The brushless motor technology is immature, the price is high, and the scope of application is limited. It should be mainly used on constant-speed equipment, such as inverter air conditioners, refrigerators, etc., and the damage of the brushless motor can only be replaced.

6.No brush, low interference
The brushless motor removes the brush, and the most direct change is that there is no electric spark generated when the brushed motor is running, which greatly reduces the interference of the electric spark to the remote control radio equipment.

7. Low noise and smooth operation
The brushless motor has no brushes, the friction force is greatly reduced during operation, the operation is smooth, and the noise will be much lower. This advantage is a huge support for the stability of the model.

8. Long life and low maintenance cost

Without the brush, the wear of the brushless motor is mainly on the bearing. From a mechanical point of view, the brushless motor is almost a maintenance-free motor. When necessary, only need to do some dust removal maintenance. Responsible editor: Gao Huijun