The main structure of a brushed DC motor consists of the stator, rotor, and brush. It generates torque through the rotating magnetic field, thereby outputting kinetic energy. The brush and commutator are in constant contact and friction, playing a role in conduction and commutation during rotation.
In a brushed DC motor, mechanical commutation is used. The magnetic poles remain static while the coil rotates. When the motor is working, the coil and commutator rotate, but the magnet and carbon brush do not. The alternating change in the coil's current direction is accomplished through the commutator and brush as the motor rotates.
In a brushed DC motor, this process involves arranging the two power input ends of each set of coils in a ring sequence, separated by insulating materials, forming a cylindrical component integrated with the motor shaft. The power is supplied through small columns made of carbon elements (carbon brushes), which, under the pressure of springs, press on two points of the ring-shaped coil power input cylinder, thereby energizing a set of coils.
As the motor rotates, different coils or different poles of the same coil are energized at different times, ensuring that the N-S poles of the coil's magnetic field have an appropriate angle difference with the nearest permanent magnetic stator's N-S poles. This interaction of magnetic attraction and repulsion generates the force to drive the motor. The carbon electrodes slide on the coil leads, similar to how a brush sweeps across a surface, hence the term "carbon brush".
The mutual sliding causes friction on the carbon brush, leading to wear and tear, which necessitates periodic replacement. The intermittent contact between the carbon brush and the coil leads also generates sparks and electromagnetic interference, disrupting electronic devices.
In a brushless DC motor, the commutation task is handled by the control circuit in the controller (generally consisting of Hall sensors and controllers, or more advanced technologies like magnetic encoders).
A brushless DC motor uses electronic commutation, with stationary coils and rotating magnetic poles. The brushless DC motor employs an electronic setup that uses the Hall element SS2712 to sense the position of the permanent magnet poles. Based on this sensing, electronic circuitry timely switches the current direction in the coils to ensure the generation of magnetic force in the correct direction to drive the motor. This approach eliminates the disadvantages associated with brushed DC motors.
These circuits form the motor controller. The controller of a brushless DC motor can achieve functionalities that brushed DC motors cannot, such as adjusting the power switching angle, braking the motor, reversing the motor, locking the motor, and using the brake signal to stop power supply to the motor. Modern electronic alarm locks for electric bikes fully leverage these functionalities.
Brushless DC motors consist of the motor body and the driver, making them a typical example of electromechanical integration. Since brushless DC motors operate in a self-controlled mode, they do not require additional start-up windings on the rotor like synchronous motors under variable frequency control, nor do they experience oscillation and step loss under sudden load changes.
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