When it comes to DC motors, in fact, we all use them every day. Especially the mobile phones we use every day, they start vibrating when there are messages or calls. This vibration is achieved using a DC motor.  

  Of course, DC motors also have many applications in other fields.  

  The most typical application is in automobiles, such as power windows, wipers, and drive motors in hybrid electric vehicles.  

  Of course, in our design, we sometimes use DC brushed motors because of their simple control and low cost.

  So, what is the working principle of a DC motor?

  1. Classification of DC and AC motors

  When it comes to DC, there is actually a classification method for motors hidden here. It is divided into DC motors and AC motors according to the different working currents. A DC motor is a motor driven by DC electricity, while an AC motor is a motor driven by AC electricity. In terms of performance, the main difference between DC and AC lies in the control of speed. The speed of a DC motor is proportional to the voltage, while the speed of an AC motor is proportional to the frequency and number of magnetic poles. Both DC and AC can be applied to servo systems, but AC motors can withstand higher currents, so in industrial applications, the common servo motor is AC servo motor. The so-called servo has nothing to do with the type and structure of the motor. As long as there is feedback and closed-loop control, it is a servo system. This feedback can be based on patterns such as position, speed, torque, etc. And the motor can be any type of motor, such as stepper motor, as well as the DC brushed motor and DC brushless motor that we will talk about today. Of course, further, DC motors can be divided into DC brushed and DC brushless motors.

  According to different excitation methods, DC brushed motors can be divided into separately excited DC motors, self-excited DC motors, and permanent magnet motors.

  Excitation is the process of energizing the stator coil to generate a magnetic field that attracts the rotor.

  Self excited DC motors can be further divided into series excited motors, parallel excited motors, and composite excited motors (series and parallel) according to different winding methods.

  2. Working principle of brushed DC motor 

  Let's start with the simplest brushed motor.    

  A brushed DC motor has a stator made of permanent magnets or coils to form a fixed magnetic field.  

  There is a fixed carbon brush or copper brush on one end of the stator, which is responsible for introducing external current into the rotor coil.  

  The rotor is composed of coils, which are connected to a commutator at the shaft end. External current passes through carbon brushes and the commutator to reach the rotor coils.

  When the coil is energized, it generates a magnetic field that is attracted by the permanent magnet, causing the rotor to rotate. After a certain angle, the rotor coil changes the direction of the current through a mechanical inverter and carbon brush, thereby changing the direction of the magnetic field and ensuring continuous rotation of the rotor.  

  Brushed motors use mechanical inverters, which have the advantages of simple structure, low price, and can provide high torque. The disadvantage is that they are prone to wear and tear, cannot be used in clean rooms, and have a limited lifespan, requiring regular maintenance.

  3. Working principle of brushless DC motor

  Most brushless DC motors (BLDC) have a stator consisting of coils and a rotor consisting of magnets.  

  So there is no need to use a brush to direct the current to the stator, which is the origin of brushless technology.  

  The principle of its motion is also magnetic field attraction or magnetic field repulsion

  The main difference between brushless DC motors and brushed DC motors is that the magnitude and direction of the current in brushless motors are directly changed by the controller.  Usually, the stator has three sets of winding wires connected to the control circuit. The control circuit uses Hall sensors to determine the position of the shaft and determine which phases need to be energized next.  

  The control system continuously changes the energized phase and the magnitude of the current to achieve control of different torques.  

  Because brushless motors use electronic commutation, they have higher reliability, quieter operation, and higher efficiency.  

  Usually, brushless motors can be made very small and have a high torque to weight ratio. However, due to the need for sensors and controllers, the cost also increases.  

  The above is about the working principle of DC motors