Why Has the DC Brush Motor not been Completely Replaced?

Since the birth of the brushless DC motor, the "ancient" brushless motor has begun to decline, but it is still a reliable choice for low-cost applications.

The main structure of the brush motor is the stator + rotor + brush, through the rotating magnetic field to obtain the rotational torque, so as to output kinetic energy. The brush and the commutator constantly contact friction, playing a conductive and transfer role in the rotation. The jump in the pole direction is accomplished by moving a contact in a fixed position that is then connected relative to the electrical contact on the motor rotor. This fixed contact is usually made of graphite. Compared to copper or other metals, the graphite does not fuse or weld together with the rotating contact during large current short circuit or open circuit / start, and the contact is usually spring borne, so continuous contact pressure can be obtained. In the brushless motor, the work of the replacement is completed by the control circuit in the controller (generally hall sensor + controller, and the more advanced technology is the magnetic encoder). The main structure of the brushless motor includes the rotor, stator, motor controller and sensor. The stator and the sensor are fixed to the housing of the motor, and the rotor is connected to the interior of the motor through an axial bearing. Inside the rotor, there is a group of permanent magnets and axial access holes installed to drain heat from the rotor through the air. During the operation of the brushless motor, the motor controller receives the potential signal read by the sensor from the rotor and determines the position and speed of the rotor accordingly. The motor controller then sends a series of current signals to the winding on the stator to motivate the magnetic field interaction between the permanent magnet on the rotor and the winding on the stator. Through this interaction, the brushless motor is able to convert electrical energy into mechanical energy and output the corresponding speed and torque.

In fact, the control of the two kinds of motors is voltage regulation, but because the brushless DC uses electronic switching, so there must be digital control can be achieved, and the brush DC is through the carbon brush switching, the use of silicon control and other traditional analog circuits can be controlled, relatively simple.

A brushed DC micro motor is a traditional motor with a rotating brush, which is connected to the rotor inside the motor, allowing the rotor to rotate and drive the machine. The brushless motor has no brush and a discrete magnetic pole inside the rotor. The brushed and brushless speeds are also different. The speed regulation mode of the brush DC micro motor is to change the position of the brush by changing the size of the contact surface between the brush and the rotor, and then change the speed of the motor. Its speed regulation mode is not very flexible, and easy to brush core wear and out of shape problems, affecting the stability of the system. In contrast, the brushless motor has more speed regulation mode. In the control system of the brushless motor, the speed regulation can be controlled automatically by controlling the current and voltage of the motor. Because the rotor inside the brushless motor is very stable, high precision speed control and torque control can be achieved. In addition, the brushless motor does not need to brush core replacement maintenance, thus saving production costs and maintenance costs.

The brush motor always maintains the following absolute advantages in the ranks of many high-end motors

1. Its structure has only one rotor, one stator and a group of brushes, which does not need a complex mechanical structure and control circuit, and the manufacturing cost is relatively low. At the same time, take the current mainstream as an example, its technology development has a history of decades, the technology is mature, and the research and development cycle is also short. This mature technology provides safe technical guarantee for manufacturing enterprises, easy to maintain, reduce maintenance costs and the risk of failure. The performance of the produced products is also becoming more stable and more popular in the market. Finally, after years of technical accumulation and practical experience, the performance has reached a relatively stable and excellent level. The introduction and innovation of new technologies constantly promote the development of brush motor industry and improve the quality and efficiency of products.

2. Fast response speed, high starting torque, first of all, the rotor part is composed of the brush and the power coil. When the current passes through the coil, a magnetic field occurs, which attracts the brush, causing the rotor to turn. Because the friction between the brush and the coil is small, the rotor has less inertia and rapid response. Second, the flow of current is controllable when startup. When the power supply is turned on, the starting torque of the motor can be controlled by changing the direction and size of the current. This feature and control mode allows it to achieve high torque start in a very short time to meet the needs of some special applications.

3. Smooth operation, good starting and braking effect. Its speed can be adjusted with the supply voltage, which allows it to accurately control the running speed to achieve smooth operation. In addition, the inertia is relatively small, so its speed response performance is very excellent, you can quickly adjust the speed. Secondly, the electromagnetic excitation mode can make it produce a large start torque, so it can accelerate quickly in a very short time, which is also one of the reasons for its good starting effect. At the same time, rapid braking can be achieved by reverse electromotive force, and there are no other common motor problems in the braking process, such as reversal or flashing. Finally, the small gap between the brush on the motor rotor and the motor driver ensures that the motor maintains efficient electrical connections at all times. This means that it can generate immediate moments when a response is needed, making it ideal for applications that require frequent start and stop, such as some automation equipment.

4. High control accuracy. It is usually used together with the reducer, decoder, make the motor output power is greater, higher control accuracy, control accuracy can reach 0.01 mm, almost can let the moving parts to stop wherever you want. Position sensors, such as Hall sensors or encoders, are installed on the motor shaft to monitor the speed and position of the motor. These sensors can very accurately measure the actual operation state of the motor and provide feedback signals to the controller. The controller can be timely corrected based on these signals to improve the control accuracy and stability.

5. No brush, low interference brushless motor to remove the brush, the most direct change is that there is no the spark generated in operation, which greatly reduces the interference of the spark to the remote control radio equipment.

6. Low noise, smooth operation of brushless motor without brush, running friction greatly reduced, smooth operation, noise will be much lower, this advantage is a huge support for the stability of the model.

7. Long life, low maintenance cost less brush, brushless motor wear is mainly on the bearing, from the mechanical point of view, brushless motor is almost a maintenance-free motor, when necessary, only need to do some dust removal maintenance.

In the basic form, BLDC motors are models of elegance and simplicity. Indeed, many of the basic science tools available for young people use a simple wire-drawing motor to show the basic principles of electricity and magnetism and how the interactions between them produce effective motion. In practice, most DC motors are more than just a combination of two simple versions of the armature poles. Among other benefits, more poles allow the motor to start more reliably from any rotation angle (the simple version has two small dead zones). Moreover, such a motor does not allow transient short circuit current to pass, some systems allow two short short circuit current to pass per turn, but many systems can not do this. The excitation coil of the stator has several configurations. The most common configuration are series winding, shunt winding and composite winding (a combination of series and shunt). In the series winding motor, the excitation coil is connected with the armature coil (by brush); in the shunt winding motor, the excitation coil is connected in parallel with the armature coil ("shunt" is another expression for "parallel").

Despite the many advantages of BLDC motors, brushed motors are still available and their performance is gradually improving. While the way the motor is designed remains relatively unchanged in many ways, there are two important developments: the widespread use of permanent magnets, and the use of IC and electronic switches for coil drive and functional feedback. Although the brushless motor can operate directly through a DC power supply, using the "suitable" drive device provides not only the necessary driving current but also the variety of protection functions required for almost every motor subsystem. Undoubtedly, DC-powered brushed motors have largely been replaced to electronically controlled brushless motors due to many reliable technical reasons. Nevertheless, having a brush motor is still an effective solution in cases of low, cost-sensitive applications or limited requirements.

The above are some professional knowledges on brush motor is difficult to be completely replaced by VSD Motors. For more relevant information, please contact us.