Brushless motor is a synchronous motor that uses DC power supply and realizes commutation function through electronic commutator without carbon brush and commutator, thus avoiding friction loss, spark interference and maintenance costs. Brushless motor has the advantages of high efficiency, high performance, low noise, low vibration, long life and high reliability. This paper introduces the classification of brushless motors.Classification of Brushless DC Motors1. External rotor brushless DC motor: This external rotor BLDC motor is basically the opposite of the type of internal rotor brushless motor. Also known as an external rotor brushless motor, it uses a rotating housing around a fixed internal component. External rotor BLDC motors typically use a higher number of permanent magnet poles on the rotor. This means more torque and smoother operation. The main disadvantage of the external rotor brushless DC motor is its slow speed. As a result, these types of motors are better suited for low-speed, high-torque applications.2. Inductive brushless DC motor:BLDC motor with Hall sensor is a motor that relies on the sensor to provide rotor position data. These types of brushless motors provide reliable performance at lower speeds. At lower rotational speeds, the sensor provides accurate data for smooth rotation. The motor with sensor will have the problem of delayed feedback at higher speeds, and harsh conditions such as magnetic interference or high temperature environment will also affect the sensor work, thus affecting the motor operation.3.  Sensorless brushless DC motor: This type of motor does not use Hall sensors. Instead, the controller relies on the back electromotive force generated in the stator coil to calculate the rotor position. These types of brushless DC motors offer the best performance at high speeds. You can also use them in high temperature environments because they do not use sensors. When the back electromotive force is too low or at rest to be read by the controller, the motor cannot be accurately controlled, so these motor types are suitable for high-speed, low-cost applications.4.  Single-phase brushless DC motor: the rotor used by the single-phase brushless motor is composed of a pair of north and south poles. This type of brushless DC motor design has its advantages and disadvantages. The advantage is that the motor can initially reach a very high rotation speed. On the downside, the performance of unipolar motors decreases significantly at lower speeds, which affects rotational stability and efficiency. Three-phase brushless motors use multiple magnetic poles on the rotor, up to 12 or more. As mentioned earlier, they are placed so that the opposite poles face each other. More magnetic poles provide smoother rotation, but at the expense of speed. Therefore, these types of brushless motors cannot reach high speeds and are suitable for applications with low speeds and high torque.5.  Sine wave drive brushless DC motor: sine wave driver rotates the rotor by continuously changing the voltage of the stator coil in a sinusoidal manner according to the rotation Angle of the rotor. The three phases of the motor "delay" for a specific amount of time, depending on the frequency.6.  Square wave drive brushless DC motor: square wave drive is the simplest way to drive. It switches the ON/OFF state of the electronic components according to the rotation Angle of the rotor, and then changes the direction of the current in the stator coil, thus making the rotor rotate. The rotor rotates once and the current direction changes 6 times.ConclusionSince the invention of the brushless motor, it has been plagued by technology, cost, process and other problems until the beginning of the 21st century. When the technical problems are gradually solved, the brushless motor with its excellent performance and characteristics will gradually be recognized by all walks of life, and the market share of brushless motor and its derivative products will grow rapidly.

Before understanding the working principle of brushless motors, let's first learn the right-hand screw rule two (ampere rule two), as shown in the following figure:When we hold the solenoid with the right hand, the four fingers point to the direction of the current, then the end pointed by the thumb is the N pole of the solenoid, and if the current is in the opposite direction, the north and South Pole are switched positions.As shown in the figure above, we wind the stator around the coil and pass a certain current through the coil to generate a magnetic field. Lorentz's law of force states that as long as a current-carrying conductor is placed in a magnetic field, it will experience a force. Due to the reaction force, the magnet will experience equal and opposite forces. When the coil through the current, will produce a magnetic field, the magnetic field is driven by the stator's magnetic pole, the same pole repel each other, the opposite pole attracts each other, if you continue to change the direction of the coil current, then the rotor induced by the magnetic field of the magnetic pole will continue to change, then the rotor will be rotating under the action of the magnetic field.The switching sequence of the current is mainly realized by the Hall sensor, which is mainly used to determine the conduction Angle of the power transistor in the electronic commutation circuit drive circuit, so as to determine the magnetic state of the armature field. The position of the pole of the rotor permanent magnet relative to the stator armature winding is detected by it so as to determine the switching sequence of the power transistor in the electronic commutation drive circuit.In addition to Hall magnetic sensors, brushless motors can also use other sensors, such as photoelectric and electromagnetic sensors. 

Structural AspectBrushless DC Motor: consists of a motor body and a driver, including a rotor, a stator, a sensor and an electronic controller. There is no brush and commutator, relying on the electronic controller to control the direction and size of the current in the stator winding according to the rotor position information detected by the sensor to realize the rotation of the rotor.Brush DC Motor: mainly composed of a stator (usually a permanent magnet), a rotor (composed of winding), a brush and a commutator. The brush and commutator change the direction of the current through mechanical contact, so that the rotor continues to rotate.Performance AspectBrushless DC Motor: higher efficiency, generally 85%-90%, more stable operation, low noise, almost no electrical spark, electromagnetic interference is small, due to the reduction of mechanical wear parts, long service life.Brush DC Motor: the starting speed is fast, the torque is large, but the mechanical friction between the brush and the commutator will lead to greater noise and heat during high-speed operation, and will also produce electrical sparks, which may cause electromagnetic interference to other equipment, and the efficiency is generally 75%-80%.Control AspectBrushless DC Motor: requires a complex electronic control unit to achieve accurate commutation control, usually using digital control technology, according to the rotor position sensor feedback information, precisely control the current in the stator winding on and off and order.Brush DC Motor: The control is relatively simple, by adjusting the size and direction of the DC voltage applied to both ends of the brush, you can control the speed and steering of the motor, which can be controlled by traditional analog circuits such as thyristor.Application AspectBrushless DC Motor: suitable for applications requiring high efficiency, noise, life and control accuracy, such as drones, electric vehicles, industrial automation equipment, high-end home appliances, etc. Brush DC Motor: Often used in cost-sensitive, precision requirements are not high, the need for large starting torque occasions, such as electric toys, some traditional power tools, small appliances, etc. Cost AspectBrushless DC Motor: Due to the need for components such as electronic controllers and position sensors, and high manufacturing process and material requirements, manufacturing costs are high.Brush DC Motor: simple structure, mature production process, low manufacturing cost. 

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Adjusting the speed of the brushless DC motor can be achieved in the following ways: 1. Regulating voltage:The input voltage of the motor is adjusted by changing the output voltage of the driver, thus changing the speed of the motor.2.PWM speed regulation:Using pulse width modulation (PWM) technology, the constant DC supply voltage is modulated into a pulse voltage sequence with fixed frequency and variable width.By changing the duty cycle of the PWM (that is, the time ratio of the high level to the low level), the average output voltage can be adjusted to change the speed of the motor. 3. Series resistance speed control:A potentiometer is connected in series in the motor circuit to adjust the speed of the motor by changing the size of the resistance.This method is suitable for low power motors, but is less cost-effective for high power motors due to the need to find a high power resistor with the right resistance value.4. Change the power-on sequence:For the case that the steering needs to be changed, it can be achieved by changing the order of the power-on of the phases.For example, the running direction of the motor can be controlled by connecting terminal dir and terminal com.                                                                                                                 

According to relevant information, the pace of life continues to accelerate.Today, around 75% of the world's population is suffering from "sub-normal" disease. With the development of the national economy and living standards, people have also begun to pay attention to their own  health question. Massage health care is a traditional Chinese skill, it is through non-drug ways to help us get rid of the "sub-health" state. Modern medical research has proved that circular massage on special acupoints is effective.Such as our respiratory system, digestive system, nervous system and blood circulation. The ring system has the function of maintaining and improving disease resistance and can help us get rid of the "sub-health" problem as soon as possible. There are two main ways of health care, one is manual massage, the other one is automatic instrument massage, such as electric massage chair. Be compared to Manual massage, automatic machine massage with its low cost, action handIn recent years, the diversity of law and other characteristics have been welcomed by more and more people.In the automatic massage equipment, the electric massage chair is the most popular one a kind of massage machine.At present, most of the popular electric massage chairs in the market are using Brush DC motor due to its mature structural design, Simple control, cheap price and other characteristics. It has been widely used. With the popularity of motor massage chairs in the market, the disadvantages of brush motors also gradually emerged, such as running noise problems, motor life questions. The problem of electromagnetic radiation generated by the motor rotation process and so on. For structural reasons of brushed DC motors, these problems cannot be solved completely. For example: brush DC motor electromagnetic radiation is mainly caused by the constant commutation of the internal brush and commutator blade during commutation, and the brush and commutator blade are an essential part of the brush DC motor, so it is accompanied by the generation of electromagnetic radiation at all times during the rotation process.Compared with the brushless DC motor, the brushless DC motor eliminates the mechanical commutation mechanism of the brushless DC motor and adopts the commutation mechanism of electronic commutation, thereby overcoming the electromagnetic radiation problem caused by the commutation of the brushless DC motor, and has the advantages of more reliable operation stability, durability and good speed regulation performance. The brushless DC motor is now used to replace the brushed DC motor, and at the same time, for the characteristics of the electric massage chair, a set of control system matching the brushless DC motor has been developed, replacing the common brushed motor on the existing market, so as to solve the problems of short life, poor reliability and electromagnetic radiation of the brushed motor. Each control circuit board is small in size, low in cost, easy to transplant to the existing massage chair system, and easy to promote.