What is Axial Flux Motors?

Motors are divided into axial and radial flux types, both operating on basic electromagnetic principles despite differing flux paths.

The motor driver adjusts the current through the rotor's coil to control its magnetic field. The fixed stator poles interact with the changing rotor field, producing the Lorentz force that drives the rotor's rotation.

Flux Path Diagram

Axial flux motors have stator poles aligned along the axis, with a cylindrical rotor. The magnetic flux passes through the rotor's central axis, and when current flows through the stator windings, it generates a magnetic field that induces a torque in the rotor according to the Lorentz force, causing it to rotate.    

Axial flux motors have a flat air gap and a short axial length, with a thin, disc-like shape, thus also known as disc motors.

Schematic diagrams of axial and radial flux motor structures

Axial flux motors offer versatile topologies adaptable to various applications, categorized into four main structures based on stator and rotor configurations:

Single-stator/single-rotor: Simple and compact, but prone to high pull, bearing stress, and noise, risking friction and reduced longevity；

Single-stator/dual-rotor: High power density, suitable for traction systems and aerospace；

Dual-stators/single-rotor: Symmetrical design, reduced unbalanced magnetic pull, suitable for wind power systems；

Multi-stator/multi-rotor: Ideal for high-torque applications like marine propulsion, large wind turbines, and hydroelectric generators；

Axial flux motor combination structure

Advantages and Limitations of Axial Flux Motors

Advantages of Axial Flux Motors

Light Weight & Small Size: YASA's axial flux motors, as industry leaders, are significantly smaller and lighter than conventional radial flux motors, with dimensions of 5L and a weight of 24kg versus 10L and 50kg. This compact design aligns with automotive lightweighting and offers greater installation flexibility.

High torque and power density: Axial flux permanent magnet motors have an effective magnetic surface area on the rotor surface, not the outer diameter, allowing for greater torque within a given volume, thus increasing torque and power density. According to YASA's official website, their motors achieve torque and power densities of 160Nm/L and 14.9kW/kg, respectively, which is four times that of traditional radial flux car motors.

High efficiency: Due to their short one-dimensional magnetic flux path, axial flux motors are highly efficient, often exceeding 96%, rivaling or surpassing the best radial flux motors on the market. They save about 15%-25% energy compared to conventional radial motors at all power levels and can sustain peak power output for longer periods.

YASA's axial flux motor structure

Low Noise and Vibration: Axial flux motors, with their uniform magnetic field, produce lower noise and vibration, ideal for noise-sensitive environments.

Energy-saving and carbon reduction: Axial flux motors reduce material use by about 50% and copper consumption to 34% of radial motors, thanks to innovations like coreless PCB stators. They are lighter, more efficient, and consume less energy, promoting energy conservation and carbon reduction.

Limitations of Axial Flux Motors

Cost Issues: Axial flux motors require special materials and manufacturing processes, which often result in higher production costs compared to traditional radial flux motors. For instance, the use of a topology without a magnetic yoke and special stator and rotor designs can lead to increased costs.

Design and Manufacturing Complexity: Axial flux motors involve intricate design and production processes, such as ensuring uniform air gaps and managing significant axial forces on the shaft. The manufacturing techniques are less advanced than those for radial motors, restricting large-scale production capabilities.

Axial Flux Motor Cross-Section Diagram

High Complexity in Design and Production

Heat Dissipation Issue: The windings' location in axial flux motors, nestled deep in the stator and between rotor discs, complicates cooling. High-load operation can lead to overheating, impacting performance and longevity.

Axial flux motors application：

Axial flux motors are currently widely applied in various fields that demand high torque density and compact space, such as new energy vehicles, aerospace, marine propulsion, robotics, and wind power generation.

New energy vehicles are an important market for the large-scale application of axial flux motors.

Axial flux motors' compactness and cost-effectiveness could resolve the cost and size issues of wheel-edge motors, advancing their widespread use. Their high power density enables sufficient torque output with light weight and reduced unsprung mass, propelling the batch application of hub motors.

Pan-good'st Specifications

Axial flux motors are crucial in optimizing commercial vehicle performance and design, with electrification opening new opportunities. Global Information forecasts a CAGR of 29.8%, with the market growing from $135 million in 2022 to $497 million by 2027.

Compact and lightweight, with power density suitable for the requirements of aviation electrification.

In 2021, the "Spirit of Innovation," part of the ACCEL project, broke the electric aircraft speed record with a velocity of 345.4 miles per hour. This fixed-wing aircraft is powered by axial flux motors, delivering a propulsion power of 400KW.

Spirit of Innovation

Industry Energy estimates that by 2035, the urban air mobility market alone will grow to over $100 billion. According to M&M, the aircraft electric motor market is expected to increase from $8.2 billion in 2022 to $12.9 billion by 2027, with a CAGR of 9.4%. Among them, axial flux motors with a power density of 5-10 kW/kg are projected to hold the largest market share during the forecast period.

Optimizing the drive structure of electric vessels for energy saving and consumption reduction.

Axial motors offer distinct advantages for enhancing ship efficiency, reducing emissions, and optimizing structure, with higher torque density translating to better energy conversion and compact design. Saietta's Propel S1 outboard engine, powered by an AFT 140 axial flux motor, achieves an overall efficiency of 62%.

Propel S1 AFT140

Mordor Intelligence forecasts that the electric vessel market will reach $11.43 billion by 2028, growing at a CAGR of 12.65% between 2023 and 2028.

The market of application for robot joint components is extensive

High-precision robots demand joint drive motors that are characterized by quick response times, high starting torque relative to their inertia, compact and lightweight designs, robustness to endure harsh operating conditions with frequent direction changes and speed variations, and the ability to handle short-term overloads.

Axial motors excel at delivering high peak torque and quick response in a millimeter-thin profile, a feat radial motors struggle with. Genesis Robotics effectively utilizes the LiveDrive axial motor's 2cm slim design to cushion the impact on robot joints during ground contact, yielding positive outcomes.

LiveDrive Axial Flux Robot Joint Motor

According to Interact Analysis, the mobile robot components market is expected to experience rapid growth at a CAGR of 44.8% starting from 2022, reaching $7.4 billion by 2027. Stratistics Market Research Consulting's data indicates that the global humanoid robot market will dramatically expand from $1.511 billion in 2021 to $26.429 billion by 2028, with a CAGR of 50.5%.

This article draws insights from the following sources: "乘“新能源汽车+机器人”东风，掀轴向磁通电机革命" by China Merchants Securities, and "轴向磁通电机有望推动汽车电动革命" by Tianfeng Securities. 

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