The Difference Between Brush Motor And Brushless Motor

The working principle of the brushed motor

The brushed motor is the first type of motor that everyone contacts, and the motor introduced in the physics class in middle school is also displayed as a model. The main structure of a brushed motor: stator + rotor + brush, which obtains a rotating torque through a rotating magnetic field, thereby outputting kinetic energy. The brush and the commutator are in constant contact and friction, and play a role in conduction and commutation during rotation. The brushed motor uses mechanical commutation, the magnetic pole does not move, and the coil rotates. When the motor is working, the coil and the commutator rotate, and the magnetic steel and carbon brush do not rotate. The alternating change of the coil current direction is completed with the commutator and the brush that the motor rotates. In a brushed motor, the process is to arrange the two power input terminals of each group of coils in order, and separate them from each other with insulating material to form a cylinder-like thing, which is integrated with the motor shaft. A small post (carbon brush) made of two carbon elements, under the pressure of the spring, is pressed from two specific fixed positions on the upper point of the 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 NS pole of the magnetic field generated by the coil and the NS pole of the closest permanent magnet stator have a suitable angle difference, and the magnetic fields are attracted and homogenous. Repel, generate power, and drive 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 carbon "brush". Sliding with each other will rub the carbon brush and cause loss. The carbon brush needs to be replaced regularly; alternating between the carbon brush and the coil terminal, electric sparks will occur, electromagnetic breaks will occur, and electronic equipment will be interfered.  

The working principle of the brushless motor:

In the brushless motor, the commutation is handed over to the control circuit in the controller (usually Hall sensor + controller, the more advanced technology is the magnetic encoder) to complete. The brushless motor adopts electronic commutation, the coil does not move, and the magnetic pole rotates. Using a set of electronic equipment, through the Hall element, the position of the magnetic pole of the permanent magnet is sensed. According to this induction, the electronic circuit is used to switch the direction of the coil current in time to ensure that the magnetic force in the correct direction is generated to drive the motor, eliminating the brush motor Shortcomings. The controller of the brushless motor can achieve some functions that cannot be achieved by the brushed motor, such as adjusting the power switching angle, braking the motor, reversing the motor, 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 is composed of a motor body and a driver, and is a typical mechatronic product. Since the brushless DC motor operates in a self-controlled manner, it will not add a start winding to the rotor like a synchronous motor started under heavy load under variable frequency speed regulation, nor will it oscillate and lose synchronization when the load changes suddenly.

The difference between the brushed motor and the brushless motor speed regulation

In fact, the control of the brushed and brushless motors is by adjusting the voltage, but the brushless DC adopts electronic commutation, so digital control can be achieved, and there are Brush DC is commutated by carbon brushes, controlled by SCR and other circuits. 1. The speed adjustment process of the brushed motor is to adjust the voltage level of the motor power supply. The adjusted voltage and current are converted by the commutator and the brush to change the strength of the magnetic field generated by the electrode to achieve the purpose of changing the speed. This process is called variable speed. 2. The speed adjustment process of the brushless motor is that the voltage of the power supply of the motor is 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 achieve the change of the rotation speed. This process is called frequency conversion speed regulation.

Differences in performance

1. The brushed motor has a simple structure and mature technology. When the motor was born as early as the nineteenth century, the practical motor produced was a brushless form, that is, an AC squirrel cage asynchronous motor. Has been widely used. However, asynchronous motors have many insurmountable defects, so that the development of motor technology is slow. In particular, brushless DC motors have not been able to be put into commercial operation. With the rapid development of electronic technology, they have only been put into commercial operation until recent years. In essence, they still belong to the category of AC motors. Shortly after the birth of the brushless motor, people invented the DC brush motor. The DC brush motor has a simple mechanism, easy production and processing, easy maintenance, and easy control; the DC motor also has a fast response, a large starting torque, and can provide rated torque from zero speed to rated speed, so once it came out It has been widely used.

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

3. The DC brush motor runs smoothly, and the starting and braking effects are good. The brush motor is regulated by voltage and speed, so the starting and braking are stable, and the constant speed operation is also stable. Brushless motors are usually digitally controlled by frequency conversion. The AC is first converted to DC, then DC to AC, and the speed is controlled by frequency changes. Therefore, the brushless motor does not run smoothly when starting and braking, and the vibration is large. Will be stable.

4. High control precision of DC brush motor DC brush motor is usually used together with gearbox and decoder to make the output power of the motor greater and the control accuracy higher. The control accuracy can reach 0.01 mm, which can almost stop the moving parts Wherever you want. All precision machine tools use DC motor control accuracy. Because the brushless motor is not stable when starting and braking, the moving parts will stop to different positions every time. They must be stopped by the positioning pin or the stopper to the desired position.

5. The DC brush motor has low cost and convenient maintenance. Because the DC brush motor has a simple structure, low production cost, many manufacturers, and mature technology, it is also widely used, such as factories, processing machine tools, precision instruments, etc., if the motor Failure, only need to replace the carbon brush, each carbon brush only needs a few dollars, very cheap. Brushless motor technology is immature, the price is high, and the scope of application is limited. It should be mainly used in constant speed equipment, such as inverter air conditioners, refrigerators, etc., and the brushless motor can only be replaced if damaged.

6. Brushless, low interference The brushless motor removes the brush. 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 on the remote control radio equipment. 7. Low noise, smooth operation Brushless motor without brushes, friction during operation is greatly reduced, smooth operation, noise will be much lower, this advantage is a huge support for the stability of the model operation. 8. Long life, low maintenance cost and less brushes. 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, just do Some dust removal maintenance is enough.