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A Comprehensive Guide to Brushless DC Motor

The brushless DC motor is increasingly popular in applications needing high efficiency, high torque, and variable speed. Once found mainly in industrial settings, these motors are now commonplace in everything.


YD Force plays a crucial role in enabling the smooth and reliable operation of BLDC motors. In fact, YD force’s advanced motor control technology ensures that these motors operate efficiently, making them ideal for a wide range of applications.  

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Table of Contents

Brushless DC Motor Structure

A brushless DC motor (BLDC) has a different structure than a standard DC motor. Learning these parts is essential to enhance the performance across different applications.


The stator is the stationary part of the motor. It provides a rotating magnetic field that spins the rotor. Typically, it contains copper windings, laminated steel core, insulation, and bearing journals.


The varying electromagnetic fields in the stator coils produce torque on the permanent magnets of the rotor, causing it to spin. By energizing the coils in a synchronized sequence, the rotor can reach very high speeds.


A brushless DC motor typically has a multi-pole rotor, with the most common configurations being 4, 6, or 8 magnetic poles. As the rotor spins, its magnetic field interacts with the stator’s magnetic field to produce thrust. The more poles, the smoother the rotor rotation and the higher the torque. But more poles also mean lower maximum speed and higher cost.

Permanent Magnets

Permanent magnets create the magnetic field in a brushless DC motor. They are made of ferromagnetic materials like iron, nickel, cobalt, and some alloys with strong magnetic properties. The magnets are placed in the stator, surrounding the rotor. Their magnetic poles form an attraction that pulls the rotor into motion.

Control Electronics

A brushless DC motor requires complex control electronics to energize the proper stator winding at the proper time. The control system senses the rotor position and switches on the correct stator phase to keep it turning.

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Types of Brushless DC Motor

What is A Brushless Motor

Inrunner vs. Outrunner

An inrunner motor has magnets attached to the inner rotor, which spins inside the stationary stator. Outrunner motors have magnets attached to the outer rotor, which spins around the stationary stator.


Outrunner motors typically have a higher torque to weight ratio, run more efficiently, stay cooler, and are less prone to cogging. However, inrunner motors can achieve higher top speeds.

Slotless vs. Slotted

Slotless brushless DC motors have windings wound in a circular shape within the motor, with no iron core. This allows for higher power density and efficiency. Slotted brushless DC motors have windings wound around the teeth of an iron core, similar to a traditional brushed DC motor.

Single-Phase vs. Three-Phase

A single AC waveform powers single-phase brushless DC motors. At the same time, three-phase brushless DC motors are powered by three separate AC power sources offset by 120 degrees.


Three-phase brushless DC motors are more efficient, powerful, and reliable. Most industrial applications utilize three-phase brushless DC motors.


However, single-phase brushless DC motors are more cost-effective, compact, and simpler. They work well for small hobby drones, computer fans, and other low-power consumer uses.

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Working Principles of Brushless DC Motor

A brushless DC motor is commonly used in various applications due to its efficiency, reliability, and precise control. These motors operate based on fundamental electromagnetic principles, and understanding their working principles can help demystify their functionality.

Commutation Process

The commutation process involves switching the current through each phase, winding in sequence. This is done using transistors or thyristors to switch the current on and off at the appropriate times. The controller uses a rotor position sensor to select the angular position of the rotor. Then, it can switch the current in each winding on and off at the proper times to make a rotating magnetic field.

Magnetic Fields and Rotation

The magnetic fields generated by the stator windings interact with the permanent magnets on the rotor to produce a force that causes the rotor to spin. As the rotor spins, the position of the permanent magnets relative to the stator windings changes. This causes the magnetic force to change both in magnitude and direction, which in turn causes the rotor to continue spinning.

Hall Effect Sensor Role

A Hall effect sensor uses a solid-state device called a Hall effect element to sense the magnetic field of the permanent magnets in the rotor. The Hall effect element produces a voltage difference across it when current flows through it in a magnetic field.


By placing multiple Hall effect sensors around the stator at precise positions, the control circuitry can decide the position of the rotor magnets.

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Advantages of Brushless DC Motor

High Output Power

With brushless DC motors, the rotor contains permanent magnets, so the magnetic field is constant. This allows for higher power densities and higher torque to weight ratios. The electronic controller provides pulsed DC power to the stator windings, which creates a rotating magnetic field to spin the rotor.

Small Size and Light Weight

A brushless DC motor is compact in size and lighter in weight. They do not contain brushes, so they don’t require space for brush gear or holders. This results in a more compact motor design with higher power density.


The absence of brushes also reduces frictional losses, so less heat is generated. Less heat means less need for bulky cooling fans and heat sinks.

Good Heat Dissipation

When you use brushless DC motors, they generate heat during operation due to power losses. Efficient heat dissipation is important to prevent overheating, which can damage the motor. Brushless DC motors use cooling fans and heat sinks to dissipate the heat.

Wide Operating Speed Range

From under 50 RPM to over 50,000 RPM, brushless DC motors have a wide operating speed range. Their speed depends on the DC voltage applied, allowing for precision control of rotational speed.

Low Noise

For hobbyists, the quiet operation of brushless DC motors is appealing for building stealthy robots, drones, or other mechanisms. In industrial settings, the low noise of brushless DC motors reduces noise pollution for workers and allows their use in facilities where excessive noise would be disruptive.


So, if low noise is a priority in your application, a brushless DC motor is an excellent choice over other options like brushed DC motors or AC Brushless Servo Motor. Its quiet, brushless operation will ensure minimal audible noise and a peaceful work environment.

High Dynamic Response

Brushless DC motors are capable of very high dynamic response. They can accelerate and decelerate quickly and reverse direction rapidly. This is because brushless DC motors have low rotor inertia since the rotor contains only permanent magnets and no copper. The low inertia allows the motor to change speed and direction quickly.

Less Electromagnetic Interference

Compared to brushless servo motors, brushless DC motors produce less electromagnetic interference (EMI). Since brushless motors have permanent magnets and electronic commutation instead of brushes, they do not create the sparking that brushed motors do. The electronic commutation of a brushless motor produces very little EMI.

Application of Brushless DC Motor

Brushless DC motors offers high power density, high efficiency, and maintenance-free operation without brushes or commutators. They are the motor of choice for many high-performance and precision motion control applications where reliability and efficiency are paramount.

Industrial Control Field

In industrial control applications, precise speed control and high torque are required. With brushless DC motors, they are maintenance-free, provide smooth, controllable power, and operate efficiently over a wide speed range. Brushless DC motors are used in computer numerical control (CNC) machines, robotics, medical equipment, and automation.

Automotive Field

From automotive applications like electric vehicles, power steering systems, and anti-lock braking systems (ABS), brushless DC motors are widely used. Compared to brushless servo motors, brushless DC motors offer higher efficiency, higher torque to weight ratio, lower maintenance, and reduced noise.

Medical Equipment Field

The brushless DC motor is typically used in medical equipment like MRI scanners, X-ray machines, and other diagnostic equipment. Its motor supplies high power in a small size, letting for the compact design of medical devices. It also generates little electromagnetic interference, which could disrupt sensitive medical sensors and electronics.

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Master the Emerging Trends in Brushless DC Motors

Auto Machinery Electric Brushless Dc Motor

For applications where size, performance, and reliability are critical, the brushless DC motor is an ideal choice. With a basic wisdom of how they work and the benefits they provide, you can nail if a brushless DC motor is the right solution for your next project. Remember, the future is brushless.

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How long do brushless DC motors last?

Brushless DC motors have a typical life expectancy of 10,000 to 20,000 hours, double that of a brushed motor. Some high-quality motor manufacturers claim a service life of 20,000 to 100,000 hours for their brushless DC motors.

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What is the maximum rpm of a brushless DC motor?

Some brushless DC motors can operate up to 224,000 revolutions per minute (RPM). The maximum RPM a brushless DC motor can achieve depends on two factors.


First, the frequency of the power source, measured in hertz (Hz), determines how fast the motor spins. A higher frequency means a higher maximum RPM. Second, motors with fewer poles, typically 2 to 6, can spin faster than motors with more poles. Each pole pair represents one revolution of the motor.

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How do I know if my brushless DC motor is bad?

If your brushless DC motor is malfunctioning, there are a few signs to look for to determine if it needs repair or replacement.


Strange noises, such as grinding or squealing sounds from the motor, often indicate damaged or worn-out bearings or other internal parts. Excessive heat buildup, especially after running for a prolonged time at high speeds, can point to issues like shorted windings or loose connections. Both conditions mean it’s time for professional servicing or replacing the motor.

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