Many of these applications are controlled by the speed and torque of the motor. The starting and driving methods of the motor can be roughly divided into two types: "① driving with a position sensor" and "② driving without a position sensor".
① Motor drive with position sensor: A motor drive method that requires the use of sensors to detect the motor speed and rotational position.
② Motor without position sensor: Motor drive method that does not require the above-mentioned sensors
① Advantages of using sensors to drive a motor: It can accurately detect the position and rotation of the motor during startup and drive, and the motor driver with a built-in hardwired logic controller can achieve smooth motor drive and rotation control from low speed to high speed. Disadvantages: Sensors such as Hall elements/Hall ICs must be installed in the motor, so the installation accuracy of the sensors and the wiring connecting the sensors and the motor controller need to be considered.
② Advantages of sensorless motor drive: It can be used to drive motors that cannot be physically equipped with sensors and motors exposed to adverse environments such as high temperature, water, and oil.
Disadvantages: Because it utilizes speed electromotive force, it performs poorly at low speeds, and the rotational position is estimated through calculation by the MCU, resulting in poor overall response performance. Furthermore, the estimation using motor current, voltage, and motor parameters (R and L of the motor windings) instead of position and rotation detection sensors is susceptible to individual motor variations.
For sensorless driving, another approach is to use a dedicated hardwired logic controller outside the MCU to start the operation with an external forced commutation signal, and then use the speed electromotive force as the position signal.
In summary, each method has its advantages and disadvantages. Therefore, it is necessary to select a motor drive method that suits the required characteristics based on factors such as the environment in which the motor is used, the level of reliability required, and the type of motor load (constant torque, constant output, square torque).
In addition, let's discuss the differences between brushless motors and brushed motors in more detail.
Structurally, brushless motors are similar to brushed motors, both having rotors and stators, but their structures are reversed. In a brushed motor, the rotor is a coil winding connected to the power output shaft, and the stator is a permanent magnet. In a brushless motor, the rotor is a permanent magnet connected to the output shaft along with the housing, and the stator is a winding coil. It eliminates the commutator brushes used in brushed motors to alternately change the electromagnetic field, hence the name brushless motor.
Disadvantages of brushed motors:
1. High friction, high wear.
Veteran model enthusiasts have encountered this problem when playing with brushed motors: after using the motor for a period of time, it is necessary to open the motor to clean the carbon brushes, which is time-consuming and laborious, and the maintenance intensity is no less than a major house cleaning.
2. High heat generation, short lifespan
Due to the structure of brushed motors, the contact resistance between the brushes and the commutator is very high, resulting in a high overall resistance of the motor and making it prone to overheating. Since permanent magnets are heat-sensitive elements, if the temperature is too high, the magnets will demagnetize, causing a decrease in motor performance and affecting the lifespan of the brushed motor.
3. Low efficiency and low output power
The overheating problem of brushed motors mentioned above is largely due to the fact that the current does work on the internal resistance of the motor, so a large amount of electrical energy is converted into heat energy. Therefore, the output power of brushed motors is not high and the efficiency is not high.
Advantages of brushless motors:
1. Brushless, low interference
The most direct change from brushless motors is the elimination of electrical sparks generated during the operation of brushed motors, which greatly reduces the interference of electrical sparks on remote control wireless devices.
2. Low noise and smooth operation
Brushless motors, without brushes, experience significantly reduced friction during operation, resulting in smoother running and much lower noise. This advantage greatly enhances the stability of the model's operation.
3. Long lifespan and low maintenance costs
Without brushes, the wear and tear on brushless motors primarily occurs in the bearings. From a mechanical perspective, brushless motors are almost maintenance-free, requiring only dust removal when necessary. A comparison clearly shows the advantages of brushless motors over brushed motors. However, nothing is absolute. Brushed motors possess superior low-speed torque performance and high torque characteristics that brushless motors cannot replace. Nevertheless, considering the ease of use of brushless motors, with the decreasing cost of brushless controllers and the development and market competition of brushless technology both domestically and internationally, brushless power systems are experiencing rapid development and widespread adoption, which has greatly promoted the development of model motors.
