Key points for selecting BLDC motors (1)
Brushless DC motors (BLDC) are widely used in industries such as industrial automation, automobiles, medical equipment, and artificial intelligence due to their long life, low noise, and high torque. BLDC has a variety of specifications and types, and in practical applications, it is necessary to select a suitable brushless DC motor to meet the performance requirements of the application product. Motor selection is the process by which engineers select a motor for a given application. This is a system-level analysis process in which engineers will repeatedly evaluate the available motor options based on the application's goals and design constraints. In essence, the process follows an engineering "design spiral" to find a motor that meets the application requirements.
Guided by the target application, the main aspects to consider when selecting a BLDC motor include: motor type, torque requirements, speed requirements, power requirements, total motor cost, and application scale limitations.
01 Choose the Right Motor Type
From the perspective of structure, brushless DC motors can be divided into two types: inner rotor and outer rotor. Fundamentally, they work on the same principle, but have different advantages and limitations.
An outer rotor motor places the stator inside and the rotor outside, rotating around the central stator. An inner rotor motor has the opposite design: the stator (stationary element) is placed outside and the rotor (rotating element) is placed inside, rotating inside the stator.
Relatively speaking, the outer rotor brushless motor has a larger diameter and better heat dissipation, which is conducive to the use of low-speed torque and is suitable for low-speed applications; while the inner rotor brushless motor has a small diameter and a faster speed, and is more suitable for high-speed applications.
BLDC motors are also divided into sensored motors and sensorless motors, depending on whether they are equipped with sensors or not.
Sensored motors use Hall sensors embedded in the motor stator. The Hall sensor is essentially a switch whose digital output is equivalent to the sensed magnetic field polarity (i.e. HI represents north and LO represents south). Sensorless motors are brushless DC motors without the Hall sensors.
The choice of sensored or sensorless motors usually depends on cost. Sensorless motors reduce the cost of sensor hardware, wiring, and manufacturing by removing the Hall sensors. At the same time, sensorless motors have a higher manufacturing yield rate - close to 100%. Therefore, more and more applications are beginning to use sensorless motors, such as low-cost variable speed motor applications such as fans, refrigerator compressors, air conditioners, and gardening tools. However, applications that require high torque at startup, such as electric tools such as electric bicycles and electric scooters, require sensored motors.
In addition, from the material point of view, high efficiency, low price, low temperature rise ferrite BLDC motor is preferred. Only when the performance requirements are strict, the volume is small, and the ambient temperature is high, should AlNiCo BLDC motor or rare earth BLDC motor be considered.
02 Identify Application Design Constraints
This is the most important part. The first task in selecting a motor is to identify the application requirements and limitations. Only by getting the direction right can you avoid wasted effort.
●Clearly Define the Application Goals
For different applications, brushless DC motors have different designs and drive methods, which makes the selection very complicated. In order to simplify the motor selection, we need to determine the core requirements based on the motor's purpose.
●Economic Considerations
Brushless motors are the longest-lasting motors, but they are not the lowest-cost motors in the world. If your project is very price-sensitive, you can still use a BLDC motor, but you may save money by using a brushed DC motor. But in the long run, brushless motor controllers have an average life of 5 times longer than standard DC motors. At the same time, brushless motor systems maintain stable performance over a long service life, so they may be the most cost-effective over the entire project life cycle. When making a decision, you must consider the trade-offs between life, performance, and cost, as well as the importance or value that important characteristics such as constant speed under variable load have.
●Size Restrictions
Before buying or using a motor, you should determine the size of the motor. Most of the time, manufacturers use a standard 4-digit naming scheme for motors. For example, a motor named 2205, where the first two digits represent the diameter of the stator (in millimeters) and the last two digits represent the height (in millimeters). If either of these two numbers is larger, the motor will handle more power and thus produce more torque. If the number is still large after weighing the pros and cons, it is called a heavier/larger motor. The following are some commonly used motor sizes. By matching them with the corresponding drones, everyone can understand the difference between these sizes more vividly.