This article first provides a brief introduction to brushed motors and brushless motors, then explains their working principles, and finally elaborates on the differences between brushed motors and brushless motors in terms of speed control methods and performance differences. Let's take a closer look together.
Introduction to Brushed Motors and Brushless Motors
1. Brushed motor
It uses carbon brushes as the two contacts for the motor power supply, and is controlled by a throttle and controller. Through secondary gear reduction and an overrunning clutch, it achieves stepless speed regulation of 0-20 km/h for electric bicycles. The brushed high-speed motors currently used are of high quality, with strong, wear-resistant reduction gears and a reasonable design, resulting in a low repair rate. Furthermore, the cost of repairing and replacing gears and the motor is low, effectively reducing the maintenance costs of electric bicycles. The brushed motor can also be easily ridden manually using the overrunning clutch and flywheel. Brushed motors utilize mechanical commutation with brushes!
2. Brushless motor
Its speed control system is more expensive than that of a brushed high-speed motor, and the controller is prone to failure during use. Electric bicycles equipped with brushless motors only achieve optimal efficiency at speeds above 35 km/h. However, we know that electric bicycles are managed as non-motorized vehicles, and their speed must be below 20 km/h. Therefore, choosing brushless motors for electric bicycles reduces efficiency and makes them less desirable. Currently, its main advantage is low noise. Brushless motors use electronic commutation and have polarity detection elements.
Working principles of brushed motors and brushless motors
1. Brushed motor
When a motor is working, the coils and commutator rotate, while the magnets and carbon brushes remain stationary. The alternating change in the direction of the coil current is accomplished by the commutator and brushes, which rotate with the motor. In the electric vehicle industry, brushed motors are divided into high-speed brushed motors and low-speed brushed motors. Brushed motors and brushless motors have many differences; as the names suggest, brushed motors have carbon brushes, while brushless motors do not.
A brushed motor consists of two main parts: a stator and a rotor. The stator has magnetic poles (wound or permanent magnet type), and the rotor has windings. When energized, a magnetic field (magnetic poles) is also formed on the rotor. There is an angle between the magnetic poles of the stator and rotor. Under the mutual attraction of the magnetic fields of the stator and rotor (between the N and S poles), the motor rotates. Changing the position of the brushes can change the direction of the angle between the stator and rotor magnetic poles (assuming the stator magnetic poles are on the first side of the angle and the rotor magnetic poles are on the second side, the direction from the rotor magnetic poles to the stator magnetic poles is the direction of motor rotation), thus changing the direction of motor rotation.
2. Brushless motor
Brushless motors employ electronic commutation; the coil remains stationary while the magnetic poles rotate. A brushless motor uses an electronic system that, through Hall effect sensors, senses the position of the permanent magnet poles. Based on this sensing, electronic circuitry switches the direction of the current in the coil in a timely manner to ensure the correct magnetic force is generated to drive the motor. This eliminates the drawbacks of brushed motors.
These circuits constitute the motor controller. The controller for a brushless motor can also perform functions that brushed motors cannot, such as adjusting the power switching angle, braking the motor, reversing the motor, locking the motor, and stopping power supply to the motor using a brake signal. The electronic alarm locks on electric bicycles now fully utilize these functions.
A brushless DC motor consists of a motor body and a driver, and is a typical mechatronic product. Because a brushless DC motor operates in a self-controlled manner, it does not require an additional starting winding on the rotor like a synchronous motor that starts under heavy load with frequency conversion speed regulation, nor does it experience oscillation or loss of synchronism during sudden load changes.
Detailed Explanation of the Differences Between Brushed Motors and Brushless Motors
I. Differences in speed regulation methods
In fact, both types of motors are controlled by voltage regulation. However, since brushless DC motors use electronic commutation, digital control is required to achieve this, while brushed DC motors use carbon brush commutation and can be controlled using traditional analog circuits such as thyristors, which is simpler.
1. The speed control process of a brushed motor involves adjusting the voltage of the motor's power supply. The adjusted voltage and current are then converted through a commutator and brushes, changing the strength of the magnetic field generated by the electrodes, thereby changing the speed. This process is called variable voltage speed control.
2. The speed control process of a brushless motor involves keeping the voltage of the motor's power supply constant while changing the control signal of the electronic speed controller (ESC). The microprocessor then alters the switching rate of the high-power MOSFET to achieve this change in speed. This process is known as variable frequency speed control.
II. Performance Differences
1. Brushed motors have a simple structure, have been developed for a long time, and have mature technology.
As early as the 19th century, when electric motors were invented, the first practical motors were brushless, namely AC squirrel-cage induction motors. These motors were widely used after the advent of AC power. However, induction motors have many insurmountable drawbacks, which has slowed the development of motor technology. In particular, DC brushless motors were unable to be commercially deployed for a long time. With the rapid development of electronic technology, they have only gradually entered commercial operation in recent years, and in essence, they still belong to the category of AC motors.
Not long after the invention of brushless motors, brushed DC motors were invented. Because brushed DC motors have a simple structure, are easy to manufacture and process, are convenient to maintain, and are easy to control; DC motors also have the characteristics of fast response, large starting torque, and the ability to provide rated torque from zero speed to rated speed, so they have been widely used since their introduction.
2. DC brushed motors have fast response speed and high starting torque.
DC brushed motors have a fast starting response, high starting torque, and smooth speed change. The vibration is almost imperceptible as the speed increases from zero to maximum, and they can handle larger loads during startup. Brushless motors, on the other hand, have high starting resistance (inductive reactance), resulting in a low power factor, relatively low starting torque, a buzzing sound during startup, and strong vibration. They can handle smaller loads during startup.
3. The DC brushed motor runs smoothly and has good starting and braking performance.
Brushed motors regulate speed through voltage adjustment, resulting in smooth starting and braking, as well as smooth operation at constant speed. Brushless motors, on the other hand, are typically controlled by digital frequency converters. They convert AC to DC and then back to AC, controlling the speed by varying the frequency. Consequently, brushless motors experience less smooth operation and greater vibration during starting and braking, only becoming stable at a constant speed.
4. High control precision of DC brushed motors
Brushed DC motors are typically used in conjunction with gearboxes and decoders to increase output power and control precision, achieving accuracy down to 0.01 millimeters. This allows moving parts to stop at virtually any desired location. All precision machine tools utilize DC motors for precise control. Brushless motors, due to their less smooth start-up and braking, cause moving parts to stop at different positions each time, requiring locating pins or limit switches to bring them to a desired stop.
5. DC brushed motors have low operating costs and are easy to maintain. Due to their simple structure, low production costs, numerous manufacturers, and relatively mature technology, DC brushed motors are widely used in factories, machine tools, and precision instruments. If the motor fails, only the carbon brushes need to be replaced, and each carbon brush costs only a few yuan, making them very inexpensive. Brushless motors, on the other hand, have less mature technology, higher prices, and limited applications, primarily in constant-speed equipment such as variable frequency air conditioners and refrigerators. When a brushless motor fails, it must be replaced.
6. 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.
7. 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.
8. Long lifespan and low maintenance costs
Without brushes, the wear and tear on brushless motors mainly occurs on the bearings. From a mechanical point of view, brushless motors are almost maintenance-free motors, requiring only dust removal maintenance when necessary.
