In the micro motor, according to the structure and working principle, it can be divided into brushed DC motor and brushless DC motor. The brushed motor has the longest history and is the most used micromotor so far. When the micromotor is running, the coil and the commutator rotate, but the magnetic steel and the carbon brush do not rotate. The alternating current direction of the coil changes with the rotation of the micromotor. To complete it with a directional device and a brush. Micro motors have low price, high torque, simple structure and easy maintenance.
However, due to the structural limitations of brushed micromotors, its shortcomings are also very obvious. For example, mechanical commutation will cause friction with the brushes, and there will be electromagnetic interference. Especially large brushed DC motors are noisy and require frequent replacement of brushes.
The brushless DC micromotor is a type of micromotor that is used more than the brushed motor. It does not use a brush device. Without the friction of the brush, the service life is greatly increased and the noise of the micromotor is reduced, but Brushless micro-motors are more expensive and are widely used in model aircraft products.
In terms of control, it must be controlled by ESC to achieve continuous operation. The rotation of the carbon brush micromotor is a winding, and the rotation of the brushless motor is a magnet whether the outer rotor or the inner rotor structure rotates. So no matter what type of micro motor is composed of stator and rotor.
In the brushless micro motor, the stator is the part that generates the rotating magnetic field and supports the rotor to rotate. It is mainly composed of silicon steel sheets, enameled wires, bearings and supports. The rotor of the micro motor is a permanent magnet (pasted with NdFeB magnets) , The rotating components of the stator's rotating magnetic field mainly include the shaft, the magnet, and the support. The number of pole pairs composed of the stator and the rotor also affects the speed and torque of the micro-motor.
The front cover, middle shell and rear cover of the brushless motor are mainly integral structural parts, which play the role of constructing the overall structure of the motor. However, the shell of the outer rotor brushless motor is also the magnetic path of the magnet, so the shell must be made of magnetically conductive material. The outer casing of the inner rotor is only a structural member, so the material is not limited. However, the inner rotor motor has one more rotor core than the outer rotor motor, and the function of this rotor core also plays the role of the magnetic circuit path.
The magnet is installed on the rotor and is an important part of the micro motor. The performance parameters of the micro motor are related to the magnet, such as power, speed, torque, etc.;
The silicon steel sheet is an important part of the slotted micro motor, but the slotless micro motor does not have the silicon steel sheet, but the micro motors with many applications still have slots. The role of magnetic circuit operation;
Rotating shaft: It is the direct force-bearing part of the rotor of the motor. The hardness of the rotating shaft must meet the requirements of high-speed rotation of the rotor.
The working principle of the brushless micro DC motor: the power system of the micro motor is three parts: the rotor, the stator and the position sensor. The position of the stator winding is determined, and a position sensing signal is generated at the determined position, which is processed by the signal conversion circuit to control the power switch circuit, and the winding current is switched according to a certain logical relationship). The operating voltage of the stator winding is provided by an electronic switching circuit controlled by the output of the position sensor.
There are three types of micro motor position sensors
1) Magnetic-sensitive position sensor: its magnetic-sensitive sensor devices (such as Hall elements, magnetic-sensitive diodes, magnetic-sensitive pole tubes, magnetic-sensitive resistors or special integrated circuits, etc.) are installed on the stator components to detect permanent Magnetic field changes generated when magnets and rotors rotate;
2) Photoelectric position sensor: A photoelectric sensor is arranged on the stator assembly according to a certain position, a shading plate is installed on the rotor, and the light source is a light-emitting diode or a small light bulb. When the rotor rotates, due to the action of the shading plate, the photosensitive components on the stator A pulse signal will be generated intermittently at a certain frequency;
3) Electromagnetic position sensor: Electromagnetic sensor components (such as coupling transformer, proximity switch, LC resonant circuit, etc.) are installed on the stator assembly. When the position of the permanent magnet rotor changes, the electromagnetic effect will cause the electromagnetic sensor to generate high-frequency modulation. signal (whose amplitude varies with rotor position).
In simple terms, the micro-motor is by changing the alternating frequency and waveform of the current wave on the input stator coil, and a magnetic field that fully rotates around the geometric axis of the motor is formed around the winding coil of the micro-motor. This magnetic field drives the permanent magnet on the rotor to rotate. , the motor starts to turn. The performance of the motor is related to factors such as the number of magnets, the magnetic flux intensity of the magnet, the input voltage of the motor, etc. It is also closely related to the control performance of the brushless motor, because the input is direct current, and the current needs The electronic governor turns it into three-phase AC power, and it also needs to receive control signals from the remote control receiver to control the speed of the motor to meet the needs of the model.
Therefore, it is the electronic speed governor that determines the performance of the micro motor. A good ESC requires the overall control of the single-chip control program design, circuit design, complex processing technology and other processes, so generally speaking, the price is much higher than that of ordinary micro motors. .
