Axial Flux Brushless DC Motors Explained
Axial flux and radial flux motors are two different configurations of electric motors, specifically permanent magnet motors, that have distinct arrangements of magnetic fields and winding layouts. The main difference between the two lies in the direction in which the magnetic flux flows through the motor and how the stator and rotor are structured. This article will cover axial flux motors.
Axial Flux Motor Layout
In an axial flux motor, the magnetic field is aligned along the axis of rotation; this means that the magnetic field lines run from one end of the motor to the other, passing through the rotor and stator in a direction that is axial (or parallel) to the motor's shaft. It has two main subassemblies: the stator and the rotor.
Figure 1: Axial Flux Brushless DC Motor Components
The rotor is the rotating part of the motor, featuring a shaft for the mounting of the application and a disc or block of permanent magnets that produce a constant magnetic field. Magnets are parallel to the shaft. It also includes black iron to enhance overall electromagnetic performance.
The stator is the stationary part of the motor. It features a housing, which supports the PCB & coils. The coils are multiturn, made of copper wire from which current flows to generate an electromagnetic field; the PCB cable assembly, meanwhile, is responsible for the required electrical input to the coil and motor. Bearings are also part of the stator assembly, which ensures the smooth rotation of the rotor.
The magnetic field generated by the stator windings interacts with the axial magnetic field of rotor magnets; this results in torque generation and motor rotation. The magnetic fields created by the rotor and stator align in the axial direction, which is a fundamental property of axial flux motors.
Benefits and Challenges of Axial Flux Motors
Axial flux motors deliver several benefits, including:
- Axial flux motors have a lower length-to-diameter (L/D) ratio, which makes them compact and flat; they are sometimes referred to as pancake motors.
- They are higher torque density motors, as they can produce an excellent amount of torque in a smaller package.
- Axial flux motors can run at reasonable speeds due to the thinness of the rotors, which results in a great power-to-weight ratio.
- The efficiency of axial flux motors is high because of the effective use of magnetic flux. It’s also worth noting that many of the motors are coreless, which reduces losses, decreases cogging, and improves the overall performance of the motor.
- An axial flux motor delivers high reliability, as the span over bearings is less and the load sharing between bearings is excellent as compared to conventional motors.
These motors are also characterized by a few challenges. One example is the difficulty in maintaining a uniform air gap between the rotor and the stator; this misalignment can cause torque ripple, which can impact the output parameters and the overall performance of the motor. While precise tooling and assembly can negate this challenge, the high manufacturing cost related to producing precise components, tooling, and assembly can be cost-prohibitive. Higher production volumes can bring down the overall cost of these motors.
Applications Using Axial Flux Motors
The compact design and high power-to-weight ratio of axial motors makes them an ideal choice for applications marked by space and weight constraints, including tattoo machines, home appliances, and drones. Applications that require low cogging, high efficiency, and high speed like robots, LiDAR, and ventilators can also benefit from the use of axial flux motors.
Portescap has decades of experience in developing miniature axial flux technologies, including disc magnet motors (DMM) and brushless DC motors like the 21BF, 26BF, and 32BF. We can also provide customization of the shaft, mounting, connection, and performance per your application requirements. Let us know how we can help you develop your next motion control solution!