Carbon brush, one end is connected to the positive and negative poles of the power supply, and the other end is pressed on the commutator. The commutator rotates with the rotor to complete the switching of the energized coils. The disadvantages of carbon brushes are noise, sparks, wear and short life. So the current trend is to replace this mechanical commutation with electronic commutation, that is, BLDC (Brushless DC Motor). Let’s look at a DC motor with a relatively large number of electrodes. Although the soybean milk machine is powered by 220 AC, the motor used inside is a DC motor. The 220V AC is rectified and turned into DC, which is directly added to the coil of the motor through carbon brushes. It has a large number of electrodes, so the torque is also large. Coreless motor, which belongs to DC brushed motor. Its rotor has no iron core, so the moment of inertia is small and the response is fast. Its volume can be made very small, and it is widely used in aircraft, focusing, instrumentation, etc.
Brushless DC (BLDC) and Permanent Magnet Synchronization (PMSM) are generally agreed upon. The Hall sensor is used to measure the rotor position, the counter electromotive force is a trapezoidal wave, and the motor controlled by six-step commutation is called DC brushless. The encoder is used to measure the rotor position, the counter electromotive force is a sine wave, and the motor with vector control (FOC) is called permanent magnet synchronous.