The emergence of brushless motors (Fig. 3) began in the 1860s, thanks to two developments: the emergence of strong, small, low-cost permanent magnets; and the emergence of small, high-efficiency electronics A switch (usually a mos tube, but sometimes a bipolar transistor with low dropout) switches the current flowing to the winding. The interaction between the surrounding fixed switching coil and the magnet on the rotating core replaces the mechanical commutation of the brushed motor. By precisely controlling the on and off of the mos tube (usually placed in the H-bridge configuration), the magnetic field on the coil is thus switched. By changing the frequency at which the mos tube is switched on and off, the motor speed can thus be controlled. In addition, through a sensor, the motor controller can obtain the position of the robot, so that the performance of the robot can be better controlled.
Figure 3: In a brushless motor, when the coil magnetic field interacts with a permanent magnet on the rotor, the coil current in the stator winding is electrically switched. In the figure, the vacant rotor belongs to the middle position.
