What is a brushless DC motor? How does it meet the needs of industries such as electric vehicles, drones, robots, and household motors?
Simply put, the brushless motor is the motor that uses an electronic commutator to replace the traditional contact commutator and brushes.
So, what does “brushless” really mean?
As the name suggests, the motor is without brushes. The traditional brush motor realizes the commutation of the current through the brush contact with the rotating part, while the brushless motor realizes this purpose through electronic control.
Components of a Brushless DC Motor
Are you curious about how a brushless motor is structured? What are its main components?
A brushless DC motor primarily consists of a stator, rotor, and optional Hall sensors.
Stator: The fixed part of the motor, usually wound with coils.
Rotor: The rotating part, typically made up of one or more permanent magnets.
Hall Sensors (optional): They continuously alter the stator coil energizing sequence based on the rotor position, ensuring the rotor constantly receives a force that drives its rotation.
How Are the Stator and Rotor of a Brushless Motor Manufactured? Let’s look further to find out.
Stator
The BLDC motor stator includes a lamination core and windings.
The BLDC stator core takes shape by stacking silicon steel sheets cut via laser cutting, wire cutting, or stamping. These stacked lamination sheets are then interlocked, laser welded, or glued together to form the complete stator core.
How does the stator core support the windings?
Motor stator windings primarily involve wrapping copper wires into the axial slots of the stator lamination stacks. Each slot holds one or more coils, and the windings are composed of multiple interconnected coils. All these windings are distributed around the stator core’s periphery to form an even number of poles.
The winding configuration can be a delta connection or a star connection. Most BLDC motors use a three-phase star-connected stator.
Rotor
The rotor in a BLDC motor consists of permanent magnets, typically made from rare-earth alloys such as ferrite and boron (NdFeB), neodymium (Nd), and samarium-cobalt (SmCo).
The rotor poles range from 2 to 8 pole pairs, with alternating north and south poles.
There are three different rotor configurations:
(a) Magnets placed on the outer periphery of the rotor,
(b) Known as an embedded rotor, where rectangular magnets are embedded in the rotor core,
(c) Magnets inserted within the rotor core.
Do you also have such a question, how Does the Rotor of a Brushless Motor Rotate? What is the Principle? Come on, let’s move on.
BLDC Motor Working Principle
In the illustrated example, the rotor has one pair of magnetic poles(N&S). While the stator has multiple copper coil groups, totaling six.
When we apply current to stator wire coils 2 and 5, these coils generate a magnetic field. The stator resembles a bar magnet, with wire coil 2 as the S pole and coil 5 as the N pole. Since opposite magnetic poles attract, the rotor’s N pole aligns with coil 2, and the rotor’s S pole aligns with coil 5.
Then, we turn off the current to coils 2 and 5 and apply current to coils 3 and 6. This generates a magnetic field where coil 3 acts as the S pole and coil 6 as the N pole. Again, the rotor’s N pole aligns with coil 3, and the S aligns with coil 6.
Similarly, we switch off current to coils 3 and 6 and apply it to coils 4 and 1. This forms a magnetic field where coil 4 is the S pole and coil 1 is the N pole, making the rotor’sN pole align with coil 4 and the S pole with coil 1. So far, the motor has rotated half a revolution… The second half of the circle and the front principle is the same, here is not to repeat.
We can simply think of brushless DC motors as, like fishing a carrot in front of a donkey, so that the donkey will always move towards the carrot.
In daily life, we encounter various brushless motors. Are you curious about their classifications?
Based on Electric Motor Design
Outer Rotor Brushless DC Motor
In an external rotor brushless motor, the magnetic steel is distributed on the outer casing, with magnets attached one by one to the outer shell. During operation, the outer casing rotates while the stator coils in the middle remain stationary.
Compared to internal rotor BLDC motors, external rotor motors have greater rotational inertia and lower speed due to the heavier outer casing. When powered, the rotor’s north pole aligns with the winding’s south pole, while the rotor’s south pole aligns with the winding’s north pole.
Where are external rotor brushless DC motors used?
Outer rotor BLDC motors apply to automotive wheels, home appliances, power tools, drones, and robots. Many automakers, including Tesla and BMW, utilize brushless motor technology in windshield wipers, EPS, oil pumps, starters, and generators.
With the advancement of lithium battery technology, brands such as BOSH, Dewalt, Ryobi, and Makita have extensively adopted brushless motors, which are energy-efficient, extending battery life and boosting work efficiency.
Drone brands like DJI and BETAFPV widely use outer rotor brushless motors, providing strong power and high energy efficiency to ensure stability and endurance during flight.
Inner Rotor Brushless Motor
In this motor, internal permanent magnets linked to the rotor shaft act as the rotor, while the wound coil serves as the stator. Simply put, the rotor is inside, and the stator is outside. The internal rotor’s close proximity to the motor’s axis provides high torque, making it suitable for driving heavy loads at startup.
Applications include low-speed settings, such as electric toys, car air conditioners, hydraulic pumps, air compressors, drainage pumps, fans, vacuum cleaners, and robotic vacuums.
Based on the Hall Sensor Type
Sensored Brushless DC Motor
“Sensored” motors integrate Hall sensors internally. When the rotor is in different positions, Hall sensors output a corresponding position signal, allowing the control circuit to control different electronic switches, energizing the stator coil, and generating magnetic attraction to rotate the rotor’s permanent magnets to the next position.
Applications include two-wheelers, three-wheelers, electric cars, logistics conveyors, high-speed centrifuges, disk drives, and printers.
Sensorless Brushless DC Motor
“Sensorless” motors lack internal sensors, using other methods to detect rotor position, commonly the “back-EMF method.” The back-EMF comparison method is divided into “hardware comparison” and “software comparison.” The software approach requires more microcontroller resources, has a more complex program, and demands precise timing, whereas the hardware approach needs no complex program, focusing solely on hardware results for commutation, although it increases hardware costs.
Applications include air conditioner compressors, engine cooling fans, fuel pumps, sleep apnea devices, and dental drills.
Based on Pole Count
Single Pole BLDC Motor
The unipolar BLDC motor’s rotor consists of one set of poles (north and south). This design offers pros and cons. The motor can rotate at extremely high speeds, a significant advantage. However, the downside is that its efficiency and rotation stability drop significantly at low speeds, so it’s ideal for high-speed applications.
Multi Pole BLDC Motor
The rotor of a multipolar motor has multiple poles, typically up to eight. These poles are positioned opposite each other. More poles mean smoother rotation but slower speeds. These brushless motors are typically used in applications requiring high torque at low speeds, as they can’t reach high speeds. The image below shows a 2-pole BLDC motor.
Based on the Power Signal
Sine Wave BLDC Motor
Sine wave commutation determines commutation points by calculating the phase difference of a sine wave current, allowing the motor winding to change current direction at the commutation point. There are two types of sine wave motors: SPWM and SVPWM (Space Vector PWM), with SVPWM offering better results. In the case of a sine motor, the waveform is sinusoidal.
Trapezoidal Wave BLDC Motor
Trapezoidal wave control technology controls coil current direction based on the BLDC motor’s phase state, generating a trapezoidal wave signal to control motor speed and torque. This signal is a sequence of periodic pulses, representing the states of the motor’s three-phase coils.
Why are more and more motors using brushless technology?
Advantages of Brushless DC Motors
High efficiency (85-90%)
High speed, generally reaching 10,000-50,000 RPM with good response and control performance
Long lifespan and minimal maintenance due to the absence of brush wear
High torque at low speeds
Low noise, as no brush friction occurs
Compact structure and small size
What are the shortcomings of the BLDC motor?
Disadvantages of Brushless DC Motors
Higher cost due to the electronic commutator and sensors
Complex control requires an electronic commutator and sensors, increasing system complexity
Electromagnetic interference that requires measures to reduce its impact on other equipment
Why do some use brushless motors and some use brushed motors? How were they different before?
Brushless Motor vs. Brushed Motor
Brushless Motor | Brushed Motor | |
Commutation Requirement | Electronic commutation based on Hall position sensor | Brush commutation |
Efficiency | There is no friction, high efficiency, generally 20%-30% higher than brush motors | The efficiency is relatively low due to friction and energy loss of the brush and commutator |
Lifespan | longer | shorter |
Speed and Control Accuracy | Through electronic control, precise speed regulation, high control accuracy, suitable for high speed occasions | Speed regulation is simple, but due to the limitation of mechanical commutator, the control accuracy is not high, and the speed is also limited |
Noise and Electromagnetic Interference | There is no brush, less noise and electromagnetic interference, and it is more suitable for equipment with higher requirements for quiet environment | Brush friction will produce noise and electromagnetic sparks, bringing certain electromagnetic interference |
Cost | The rotor requires permanent magnets and the controller is complex and requires additional sensors (such as Hall sensors), resulting in higher costs | Lower cost |
Application | It is used in drones, industrial automation equipment, electric vehicles and medical equipment where efficiency, life and noise are required | Suitable for equipment requiring simple control and low cost, such as household power tools, toys |
Why Are Brushless Motors Replacing Brushed Motors? The unique aspect of brushless motors lies in their electronic commutation system, which replaces brushes in traditional motors, reducing wear, noise, and electromagnetic interference. Now, brushless motors have become the preferred choice in fields like drones, robotics, and automotive industries.
Knowing so much knowledge about brushless motors, what parts can we make for brushless motors?
The core business of Lamnow is the manufacture of standard parts and custom products for stator and rotor cores of brushless motors in China. Of course, we can also supply standard parts of brushless motors.
If you are interested in going deeper into the details of brushless motors or have a need for customized motor core parts, feel free to contact.