Blog

Home > Blog

Table of Contents

Brushless DC motor VS DC servo motor

Introduction

With the rapid development of industrial automation and intelligence, dc motor kit play a vital role as the core power components of these systems. Among them, high torque brushless dc motor and DC servo motors have attracted much attention due to their unique performance and wide range of application scenarios.

In daily motor selection consultations, we often meet this situation. The customer’s application may require a DC servo motor, but mistakenly choose a BLDC electric motor due to a lack of understanding of the differences.  As a result, the motor cannot fully meet their application or control requirements.

Discover the key differences between DC servo motors and brushless DC motors in this comprehensive guide. Designed for structural engineers, this article will help you to make informed decisions and choose more suitable motor power solution for your equipment and application.

Basic overview of brushless DC motors and Brushless servo motors

Brushless DC motors consist of a motor body and a driver, with the market primarily offering 2-pole and 4-pole square wave motors. These motors can be either sensored brushless motor with Hall sensors inside, or sensorless brushless motor, without Hall sensors. Both types require matching drivers to operate.

On the other hand, DC servo motors generally feature 5-pole and 10-pole sine waves. They are divided into brushed dc motor with encoder and brushless dc motor with encoder, both equipped with encoders for high-precision control. This article will focus on analyzing the differences between sensored brushless motor with hall sensor and brushless servo motors with encoders.

Does your equipment need a brushless DC motor or a DC servo motor?

1) From the perspective of internal feedback components

Brushless DC motors is a sensored brushless motor with built-in Hall sensors typically have 8 wires: 3 power wires (U, V, W) and 5 Hall sensor wires (5V, 0V, Hu, Hv, Hw). After connecting the motor to the external driver, you can control the motor’s start, stop, forward/reverse rotation, and speed adjustment.

BLDC electric motor offer versatile speed control options based on the performance of their drivers. The most common methods include:

lManual Speed Control with a 10K Potentiometer

lPWM (Pulse Width Modulation) Speed Control

l0-5V Analog Speed Control

lRS485 Modbus Command Speed Control

Each manufacturer and model of brushless DC motor drivers may support different types of speed control. Therefore, it is crucial to verify the supported methods with the brushless DC motor driver manufacturer beforehand.

A brushless servo motor is equipped with a built-in encoder, which can be customized according to customer requirements. Here are the common types of encoders available:

lOptical Incremental Encoder

lMagnetic Incremental Encoder

lOptical Absolute Encoder (17-bit)

lMagnetic Absolute Encoder (17-bit)

lResolver

lAnalog Sine-Cosine Encoder

Selecting the appropriate encoder type depends on your specific feedback and control requirements. The high precision of these feedback components allows brushless DC servo motors to achieve high-precision control, making them ideal for applications requiring precise positioning and speed regulation.

From the perspective of precision control

Brushless DC motors are only suitable for low-precision speed adjustment and control. There will be a 5% to 10% no-load speed difference between different motors, making it challenging to achieve synchronized control of two or more motors, such as simultaneous start and stop or linear movement.

DC servo motor, because the high precision of its encoder, the matched servo driver, is key to achieving precise position control, speed control, and torque control. Users can choose the appropriate control mode based on their specific application requirements.

In short, if your equipment requires high-precision control, such as starting and stopping at the same time, or positioning at a specific location, then brushless dc servo motor is the best choice.  If precision control is not a concern, then a DC sensored brushless motor with a Hall sensor and driver is a great option, offering a competitive cost advantage.

From the perspective of torque changes during speed control

Brushless DC motors have a obvious advantages for fixed speed operation, especially in high-speed operation conditions, such as juice machines and grinders, power tools, etc. They perform best above 500 RPM. Some advanced drivers can manage speeds down to 300 RPM.

However, below 500 RPM, sensored brushless DC motors with Hall sensors almost without torque and cannot meet high torque demands at low speeds, such as during climbing. This is why it’s easy to slide backwards when climbing or lifting. The highest rated torque based on brushless dc motor is based on motor’s rated speed. And the rated torque will be reduced by 10% to 15% during speed decreases, and the lack of torque becoming especially noticeable when motor’s speed below 500 RPM. 

Why does torque decrease when motor speed reducing for permanent magnet sensored brushless motor?

Many people believe that lowering the speed of a BLDC motor should increase its torque. However, torque actually decreases during speed reducing. This is because brushless DC motors adjust speed through resistance, effectively lowering the motor’s voltage and power, which reduces torque instead of increasing it.

To address this issue, it’s crucial to accurately evaluate the motor’s speed range. Using gear reducers can help lower the motor’s maximum operating speed, thereby increasing the motor’s torque proportionally to the gear reduction ratio.

There are four main types of gear reducers available in the market:

lStandard Gear Reducers

lWorm Gear Reducers

lPlanetary Gear Reducers

lThe Four Major Series Reducers

Each type differs in lifespan, precision, efficiency, noise, size, and cost. Users can choose the appropriate reducer based on their specific needs. We will publish articles in the future comparing different reducers to help you make an informed decision.

Brushless DC servo motors, due to their characteristics, support constant torque speed adjustment. This means the motor’s torque remains unchanged when adjusting speed from high to low speed. Thus, brushless servo motors can ensure sufficient torque output at low speeds, meeting the torque requirements in low-speed ranges.

Recommendations:

lFor Low-Speed Requirements: If your equipment requires the motor to run below 500 RPM, we recommend choosing a BLDC servo motor with encoder. Its constant torque speed adjustment feature effectively addresses the torque deficiency at low speeds.

lFor High-Speed Operation: If your equipment does not require low-speed operation and runs at a constant high speed, a brushless DC motor is the best choice, offering the best cost-effectiveness.

By understanding these factors, you can make an informed decision that ensures optimal performance and efficiency for your specific application.

From the perspective of driver communication

BLDC Motor Controller:

For cost-saving and budget considerations, the most common communication methods for brushless DC motor drivers with Hall sensors is RS232 or RS485. Some models might not include any communication capabilities at all. If you require specific communication features, it is crucial to discuss and confirm these needs with the brushless DC motor controller manufacturer in advance.

DC Servo Motor Controller:

DC servo motor drivers typically support a wider range of communication methods, including CAN bus, EtherCAT, RS485 and RS232. Customers can choose the communication method that best suits their preferences and requirements. It’s essential to confirm with the brushless DC servo motor and driver manufacturer whether the selected driver meets your desired communication way. Additionally, inquire about the available communication modes and whether there is an English version of the upper machine software.

From the perspective of motor holding torque

Holding torque refers to a motor’s ability to maintain torque when the motor speed is zero. This can be easily tested.

lSensored Brushless DC Motor: When the driver speed is set to zero, even if the driver is not powered off, the motor shaft has no torque and can be easily and flexibly rotated by hand.

lBrushless DC Servo Motor: When the motor speed is set to zero on the upper machine software, as long as the driver is not powered off, the motor shaft still maintains torque. If the motor power is relatively high, it is difficult to rotate the motor output shaft by hand. This torque-holding feature is known as motor holding torque.

Holding torque plays a important role in applications involving climbing and lifting. If you stop midway during climbing or lifting to load cargo, the moment the motor brake is released, without holding torque, the motor may not enable quickly enough. The load’s weight could then cause the motor to stall, leading to uncontrolled descent or slippage.

This is why we recommend brushless DC servo motors for such applications. If your equipment involves climbing or lifting, do not hesitate to choose a brushless servo motor. It will save you a lot of time and effort in achieving optimal performance during testing and operation, even the cost is higher than the brushless dc motor option.

From the perspective of motor size

Many equipment and application have strict requirements for volume and size. Brushless DC servo motors offer significant advantages in terms of size due to their high pole count and high motor density. Let’s illustrate this with an example:

lSensored Brushless DC Motor: A typical 600W, 48V, 3000rpm/min brushless DC motor with Hall sensors and 4-pole pairs (square wave) would have a flange diameter of 86mm or 90mm and a motor body length of 105mm.

lBrushless DC Servo Motor: In contrast, a BLDC servo motor with encoder and 10-pole pairs (sine wave) would only require a flange diameter of 60mm and a motor body length of approximately 120mm.

If your equipment has strict space and volume requirements, brushless DC servo motors is a good choice. Their compact design allows for more efficient use of space without compromising on performance.

From the perspective of driver control difficulty

Brushless motor driver is relatively straightforward. They primarily assist users in achieving four main functions:

lStart

lStop

lSpeed Adjustment

lForward and Reverse Rotation

Some users might also have requirements for rapid start, rapid stop, and speed control (both open-loop and closed-loop). These functions are relatively simple, making the controllers easy for users to get started with.

Servo motor drivers are more complex, requiring customers to program with PLC and send commands to control the driver. This demands a higher level of technical expertise from users.

For those who have previously used bldc DC servo motors, these tasks are quite manageable. However, for technicians who have not worked with servo motors before, it may take more time to understand and become familiar with the control methods.

Regardless of the user’s experience level, it is crucial to have timely and professional technical support from the servo controller manufacturer. This is an essential factor to consider before purchasing the product.

Permanent Magnet Brushless DC Motor VS. DC Servo Motor Summary

TypeBrushless DC MotorsDC Servo Motor
CostLowHigh
Precision ControlSuitable for low-precision speed adjustment and controlSuitable for high-precision position control, speed control, and torque control
Torque VariationSignificant torque drop at low speeds (almost without torque below 300 RPM)Supports constant torque speed adjustment, suitable for high and low speeds
ControlSimple, mainly achieves start, stop, speed adjustment, and forward/reverse rotationComplex, requires programming and command control
Feedback ComponentsWith Hall sensors or without hall sensorEncoder, various types (optical incremental, magnetic incremental, optical absolute, etc.)
Communication MethodCommonly RS232 or RS485, some models may lack communication capabilitiesSupports multiple communication methods such as CAN bus, EtherCAT, RS485
Holding TorqueNo holding torque when speed is set to zeroMaintains torque when speed is set to zero
SizeLargerSmaller, suitable for devices with strict space requirements
ApplicationSuitable for high-speed applications that do not require high control precision, such as juicers, blenders, mixers, water pumps, oil pumps, and power tools.Suitable for high-precision applications like AGVs, RGVs, lifting equipment, service robots, unmanned vehicles, medical devices.

Conclusion

Both types of motors play crucial roles in different fields, contributing significantly to the rapid development of industrial automation and intelligence. They are indispensable power components on the path to high-speed advancement.

So, does your equipment or application require a permanent magnet brushless DC motor or a brushless DC servo motor? Do you have the answer now?

Latest Post
Hey,I‘m Jack.

Because of my work, my customers may know more about how to choose suitable motor power solution for their application. lf you have any questions about this, please feel free to contact with me!

Contact Us Anytime

Send Us Your Comment

Contact for Faster Size Drawing