Brushless motors: Brushless DC motors consist of a motor body and a driver, and are a typical mechatronic product. Because brushless DC motors operate in a self-controlled manner, they do not require an additional starting winding on the rotor like synchronous motors that start under heavy loads with frequency conversion speed regulation, nor do they experience oscillations or loss of synchronism during sudden load changes. The permanent magnets in small and medium-capacity brushless DC motors now mostly use high-energy-level rare-earth neodymium iron boron (Nd-Fe-B) materials. Therefore, the size of a rare-earth permanent magnet brushless motor is one frame size smaller than that of a three-phase asynchronous motor of the same capacity.
Brushed motors: Brushed motors are rotating electric machines that convert electrical energy into mechanical energy (electric motors) or mechanical energy into electrical energy (generators) by incorporating brushes. Unlike brushless motors, brushes are used to introduce or extract voltage and current. Brushed motors are the foundation of all motors, characterized by fast starting, timely braking, smooth speed adjustment over a wide range, and relatively simple control circuitry.
Part 1: Knowledge of Brushed Motors
A brushed motor contains a brush assembly that converts electrical energy into mechanical energy, or vice versa. Brushed motors are the foundation of all motors, offering advantages such as rapid start-up, timely braking, smooth speed regulation over a wide range, and relatively simple control circuitry.
A brushed motor mainly consists of a stator and a rotor. The stator has magnetic poles (windings or permanent magnets), and the rotor has windings. When electricity is applied, a magnetic field (magnetic poles) is also generated on the rotor. Under the influence of the stator's magnetic field (N and S), the motor rotates. By changing the position of the brushes, the angle between the stator and rotor magnetic poles can be changed (assuming the direction of the rotor's magnetic poles towards the stator's magnetic poles is the direction of the motor's rotation), thus changing the direction of the motor's rotation.
It is important to note that brushed motors are powered by direct current, so they are also commonly referred to as "DC motors".
Part Two: Knowledge of Brushless Motors
A brushless motor consists of a motor body and a driver. Since a brushless motor operates in a self-controlled manner, it does not require a variable frequency speed control method. Heavy-load starting motors do not require an additional starting winding on the rotor, and they will not oscillate or lose synchronism due to sudden load changes.
Brushless motors use semiconductor switching devices for electronic commutation, replacing traditional contact commutators and brushes with electronic switches. A brushless motor consists of a permanent magnet rotor, a multi-pole winding stator, and a position sensor. The position sensor, based on changes in rotor position, commutates the stator winding current in a specific sequence (i.e., it detects the position of the rotor poles relative to the stator windings, generates a position detection signal, and a signal conversion circuit controls the power switching circuit, switching the winding current according to a specific logic). The electronic switching circuit, controlled by the position sensor output, provides the operating voltage to the stator windings.
Brushless motors are highly reliable, produce no commutation sparks, and have low mechanical noise, making them widely used in high-end video recorders, electronic instruments, and automated office equipment. It's important to clarify that many people mistakenly believe brushless motors are the same as DC motors, hence the name "brushless DC motor." In reality, a brushless motor is an AC motor, specifically a three-phase AC permanent magnet motor.
I. What are brushless motors and brushed motors?
1. Brushless motor: It is an electromechanical integrated product consisting of a motor body and a driver.
2. Brushed motor: A rotary motor that contains brushes to convert electrical energy into mechanical energy or vice versa.
II. Differences between brushless motors and brushed motors
The difference between brushless motors and brushed motors
1. Structure: The presence or absence of carbon brushes is the most obvious difference between brushless motors and brushed motors;
2. Service life: Brushless motors have a long service life, typically 7-10 years; brushed motors have a service life of approximately 2-3 years.
3. Energy consumption: Brushless motors consume less power, only one-third that of conventional brushed motors;
4. Noise: Brushless motors are very quiet and run smoothly because they do not have carbon brushes. Brushed motors, on the other hand, are noisy and prone to damage due to the presence of brushes.
5. Price: Brushless motors do not have carbon brushes, which means that an additional controller is required, resulting in higher costs and prices. Brushed motors are relatively inexpensive.
Brushed motor
III. Differences in Testing Brushless Motors and Brushed Motors
1. Brushless motor testing plan and items
(1) Brushless motor whole machine test: Test items: AC withstand voltage, insulation resistance, inter-turn withstand voltage, DC resistance, no-load performance, phase loss detection, load performance (power, speed, Hall characteristics);
(2) Stator test of brushless motor: AC withstand voltage, insulation resistance, inter-turn withstand voltage, DC resistance, coil inductance, direction of rotation, back electromotive force, phase sequence, Hall effect characteristics;
(3) Brushless motor rotor test: back electromotive force, Hall characteristics (high and low levels, frequency, duty cycle, Hall waveform), phase difference (back electromotive force, Hall, back electromotive force and Hall);
(4) Brushless motor dynamometer test: voltage, current, power, speed, torque, efficiency, (cycle) life, temperature rise.
Brushless motor testing equipment
2. Brushed Motor Testing Plan and Items
The brushless motor is tested for AC withstand voltage, insulation resistance, no-load characteristics, current waveform, speed, and direction of rotation.
Brushed motors use mechanical commutation, where the magnetic poles remain stationary while the coils rotate. When the motor is working, the coils and commutator rotate, while the magnets and carbon brushes do not. The alternating change in the direction of the coil current is accomplished by the commutator and brushes, which rotate with the motor.
In a brushed motor, the process involves arranging the two power input terminals of each set of coils into a ring, separated by insulating material, forming a cylindrical structure that is integrated with the motor shaft. Power is supplied to a set of coils through two small carbon brushes, which, under the pressure of springs, press against two points on the upper coil power input ring cylinder from two specific fixed positions.
As the motor rotates, different coils or different poles of the same coil are energized at different times, creating a suitable angle difference between the N and S poles of the coil that generate the magnetic field and the N and S poles of the nearest permanent magnet stator. Opposite magnetic poles attract each other, and like poles repel each other, generating a force that drives the motor to rotate. The carbon electrodes slide on the coil terminals, like a brush brushing a surface, hence the name "carbon brush."
Sliding between the carbon brushes causes friction and wear, requiring regular replacement. The alternating switching between the carbon brushes and the coil terminals can generate electrical sparks, producing electromagnetic interference that can disrupt electronic equipment.
The differences between brushed motors and brushless motors include whether they are equipped with ordinary brushes and commutators, their application range, service life, performance, and energy saving.
A brushed motor is a rotating electric machine that contains brushes and converts electrical energy into mechanical energy (motor) or mechanical energy into electrical energy (generator). Brushed motors are the foundation of all electric motors, characterized by rapid starting, timely braking, smooth speed regulation over a wide range, and relatively simple control circuitry. Commutation in a brushed DC motor is always achieved through the contact between graphite brushes and the annular commutator on the rotor. In contrast, a brushless DC motor uses Hall effect sensors to feed back the rotor position to the control circuit, allowing it to determine the precise timing of commutation.
Brushed motors are chosen by most domestic electric bicycle manufacturers. They use carbon brushes as the two contacts for the motor's power supply, controlled by a speed control handle and controller. Through secondary gear reduction and an overrunning clutch, they achieve stepless speed regulation from 0-20 km/h. High-speed brushed motors use high-quality metal, 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 relatively low, effectively reducing the maintenance cost of electric bicycles. Brushed motors can also achieve easy manual riding using an overrunning clutch and flywheel. Brushed motors employ brushed mechanical commutation.
Brushless motors in electric bicycles require speeds of 35 km/h or higher to achieve optimal efficiency. However, as electric bicycles are regulated as non-motorized vehicles, their speed must be below 20 km/h. Therefore, choosing brushless motors for electric bicycles reduces efficiency and makes them less desirable. A key advantage is low noise. Brushless motors use electronic commutation and also include polarity detection elements.
Brushless motors and brushed motors are two commonly used types of motors in mechatronics. Although their structures differ, both have wide applications. This article will detail the differences between brushless motors and brushed motors.
1. Structural Principles
A brushed motor is a traditional DC motor, consisting of a permanent magnet, an armature, brushes, and wheels. In a brushed motor, electrical energy enters the brake, generating an electromagnetic field. When the brushes contact the armature, a change in magnetic flux is created, driving the armature to rotate and simultaneously generating voltage. The contact between the brushes and the armature leads to losses and the generation of unstable electrical sparks.
Brushless motors, also known as BLDC motors (brushless DC motors), consist of a permanent magnet, armature, controller, rotor, and inductor. The control of a brushless motor is achieved by an external controller. It uses zero-brush technology, meaning there are no brushes, thus offering advantages in high-speed applications such as flexibility and low losses. Because the step-by-step control of a brushless motor can be performed electronically, it also offers higher precision. While brushless motors have a more complex structure and are more expensive, they offer superior performance.
2. Operating characteristics
Brushed motors produce high torque at low speeds, but the torque decreases as speed increases. Brushed motors have relatively low energy efficiency, approximately 50-60%, primarily due to friction losses between the brushes and the armature, and heat losses caused by current.
Brushless motors offer higher efficiency and more stable performance, with a power factor typically exceeding 90%. They perform well at both low and high speeds. Brushless motors also have a longer lifespan because they lack brushes, frictional losses, and electrical sparks, allowing them to operate for extended periods.
3. Advantages and disadvantages
The advantages of brushed motors are their low cost and high initial starting force, and they are also suitable for many small motor applications. The manufacturing and maintenance costs of brushed motors are relatively low because their technology is mature.
Brushless motors are among the most commonly used motors in modern industry, offering higher performance, efficiency, precision, and a longer lifespan. They are widely used not only in home appliances and automobiles but also play a vital role in industries such as manufacturing, healthcare, and aerospace. However, the manufacturing and maintenance costs of brushless motors are relatively high.
4. Application Scenarios
Brushless motors are widely used in power tools, home appliances, electric vehicles, automated warehousing equipment, medical devices, robotics, drones, and other industries. Their high efficiency, precision, and accurate control are highly valued. Brushless motors can also be controlled at different voltages and frequencies via inverters, reducing electromagnetic interference from rapid braking and high-speed acceleration, and enhancing the accuracy of speed control.
Brushed motors are used in toys, cameras, model airplanes, and other applications. However, due to their lower efficiency and accuracy, most robot manufacturers, as well as many ATHLETE robot manufacturers, have switched to brushless motors for their robots.
Overall, with continuous technological advancements and expanding applications, brushless motors are gradually replacing brushed motors as the mainstream choice for mechatronics. Excellent brushless motors feature low noise, low vibration, no brushes, high efficiency, reliability, compact size, and portability. Brushed motors are still used in a few applications due to their simplicity and low cost, but this is only for small-scale applications with low performance requirements. With continuous technological progress, rising living standards, and the expanding military, civilian, and industrial markets, brushless motors are destined to become a new trend in mechatronics.
