- Author: Johnny Liu (CEO at Dowway Vehicle)
- Technical Reviewer: Dr. Aris Thorne, Lead Powertrain Systems Architect
- Published: July 24, 2026
- Updated: July 24, 2026
- Estimated Read Time: 12 Minutes
Table of Contents
0. Executive Summary
- Definition: An Axial Flux Motor (AFM) is a brushless permanent magnet or induction electric motor where magnetic flux lines flow parallel to the axis of rotation across a flat disk, rather than radially across a cylinder.
- Performance Metrics: Delivers up to 30%–40% higher torque density and 2x–3x higher continuous power density ($\ge 40\text{ kW/kg}$) compared to state-of-the-art radial flux electric motors.
- 3 Core Tech Pillars:
- Stator Materials & Architectures: Soft Magnetic Composites (SMC), Yokeless & Segmented Armatures (YASA), and PCB Stators.
- Rotor Engineering: Dual-rotor configurations, Halbach magnet arrays, and segmented/skewed NdFeB magnets.
- Thermal Management & Manufacturing: Direct stator immersion oil cooling, micrometer air-gap tolerance control, and automated laser-welded windings.
1. Introduction: The Shift in Electric Motor Design
For over a century, the electric vehicle (EV) industry and industrial automation relied almost exclusively on Radial Flux Motors (RFM). In a radial flux design, magnetic flux travels radially outward across a cylindrical air gap between concentric rotor and stator elements. While reliable and mature, conventional radial flux architectures are reaching physical limits in power density, copper fill factors, and volumetric efficiency.
As performance demands intensify across electric hypercars, Urban Air Mobility (eVTOL aircraft), heavy commercial fleets, and high-degree-of-freedom humanoid robotics, powertrain engineers require higher torque-to-weight ratios.
Enter the Axial Flux Motor (AFM). Though historically restricted by manufacturing complexity and axial force management, modern breakthroughs in materials science, 3D electromagnetic simulations, and automated assembly have made axial flux machines commercially viable.
Understanding the electromagnetic physics of axial flux motors—along with the three core technological innovations driving their commercialization—is essential for any engineer or leader designing next-generation electric mobility systems.
2. Part 1: Fundamental Principles of Axial Flux Motors
2.1 Physics & Electromagnetic Geometry
The distinction between radial and axial flux machines lies in the geometric orientation of the air gap and magnetic field vector relative to the shaft axis:
RADIAL FLUX MOTOR (RFM) AXIAL FLUX MOTOR (AFM)
[Stator Outer Ring] [Rotor Disk 1]
| Magnetic Flux | ==> Axial Magnetic Flux (Parallel)
[Rotor Inner Cylinder] [Stator Disk]
(Radial Direction) | ==> Axial Magnetic Flux (Parallel)
[Rotor Disk 2]
- Radial Flux Motor (RFM): Magnetic flux vectors extend perpendicular to the shaft axis. The active electromagnetic volume scales linearly with length ($L$) and quadratically with radius ($R$), yielding torque proportional to diameter squared times length: $$T_{\text{radial}} \propto D^2 \cdot L$$
- Axial Flux Motor (AFM): Magnetic flux vectors flow parallel to the rotational axis across one or more disk surfaces. The torque generation surface area depends directly on the outer diameter ($D_{\text{out}}$) and inner diameter ($D_{\text{in}}$) of the stator disks. Electromagnetic torque scales with the cube of the diameter: $$T_{\text{axial}} \propto D_{\text{out}}^3 – D_{\text{in}}^3$$
Because torque scales cubically with diameter in an axial flux machine, increasing the radius yields higher torque gains than adding length to a radial flux motor. This enables a thin “pancake” form factor with a short axial footprint.
2.2 Quantitative Comparison Matrix: Axial Flux vs. Radial Flux
| Metric / Parameter | Axial Flux Motor (AFM) | Radial Flux Motor (RFM) | Design Advantage |
|---|---|---|---|
| Magnetic Flux Line Vector | Parallel to shaft axis ($\parallel$) | Perpendicular to shaft axis ($\perp$) | Changes physical footprint from cylinder to disk. |
| Form Factor / Geometric Profile | Short axial length, large radial diameter (“Pancake”) | Long axial length, small radial diameter (“Drum”) | Fits tight wheel hubs, transmission housings, and aircraft nacelles. |
| Volumetric Torque Density | Very High ($30\% – 40\%$ higher) | Moderate | Significant weight savings for equal torque output. |
| Gravimetric Power Density | Extremely High ($30 – 45+\text{ kW/kg}$) | Standard ($8 – 18\text{ kW/kg}$) | Essential for weight-sensitive systems (eVTOL, Supercars). |
| Copper End-Turn Volume | Minimal / Shorter active winding end-turns | Substantial (non-active end-turn copper overhang) | Cuts passive copper weight and internal resistance losses ($I^2R$). |
| Heat Dissipation Capability | Direct stator surface exposure | Limited by outer housing jacket | Enables direct contact immersion or channel oil cooling. |
| Axial Magnetic Pull Attraction | Heavy structural load across air gap | Balanced radially across center shaft | Requires rigid structural housings and precision bearing control. |
| Manufacturing Automation | High-volume automated lines expanding | Fully mature, standardized globally | Production costs drop as tooling scales globally. |
2.3 Key Operational Advantages Driving Industry Adoption
- High Torque-to-Weight Ratio: By placing active copper and magnet mass at the maximum radius ($R_{\text{outer}}$), AFMs maximize the moment arm of electromagnetic forces, yielding high specific torque ($\text{N}\cdot\text{m/kg}$).
- Lower Passive Copper Overhead: In radial flux machines, a large portion of copper wire sits outside the active stator iron slot (the “end turns”), adding electrical resistance without generating torque. Axial flux coils feature tighter, shorter end-turns, minimizing $I^2R$ copper heat losses.
- Packaging Flexibility: The thin disc shape allows axial flux motors to integrate directly into transmission gearboxes, mount inside wheel hubs (In-Wheel Motors), or stack back-to-back on a single shaft to form high-density multi-motor powertrains.
3. Part 2: The Three Core Technologies Advancing Axial Flux Motors
While the axial flux concept dates back to Michael Faraday’s early disc motor experiments in 1831, early production stalled due to material constraints and structural forces. Today, three core technology breakthroughs have solved these historical bottlenecks.
+-----------------------------------------------------------------------------------+
| AXIAL FLUX CORE TECHNOLOGIES |
+------------------------------------+----------------------------------------------+
| Core Tech #1: Advanced Stators | • Soft Magnetic Composites (SMC) |
| | • Yokeless & Segmented Armatures (YASA) |
| | • Etched PCB Stators |
+------------------------------------+----------------------------------------------+
| Core Tech #2: Rotor Optimization | • Dual-Rotor Configurations (SDR / DSR) |
| | • Halbach Array Flux Concentration |
| | • Magnet Segmentation & Skewing |
+------------------------------------+----------------------------------------------+
| Core Tech #3: Thermal & Assembly | • Direct Immersion & Channel Oil Cooling |
| | • Micrometer Air-Gap Precision Control |
| | • Automated Laser-Welded Windings & Potting |
+-----------------------------------------------------------------------------------+
Core Technology #1: Stator Innovation & Advanced Materials
The Core Challenge
Conventional radial motors use planar electrical steel laminations stacked along the shaft axis. In an axial flux motor, magnetic flux flows in three dimensions through 3D paths across the stator teeth. Stamping and bending 2D lamination sheets to form a 3D axial flux stator core creates high eddy current losses and manufacturing complexity.
Engineering Solutions:
- Soft Magnetic Composites (SMC):
- Mechanism: SMC materials consist of high-purity iron powders coated with an electrically insulating micro-thin ceramic layer.
- Advantage: SMC exhibits isotropic magnetic properties, meaning flux travels with equal permeability in all three spatial dimensions ($x, y, z$).
- Production Effect: SMC components are formed via high-pressure powder metallurgy die pressing, enabling 3D stator pole shapes with low material waste, low high-frequency eddy current losses, and high net-shape precision.
- Yokeless and Segmented Armature Topologies (e.g., YASA Architecture):
- Mechanism: Traditional stators use a heavy outer back-iron “yoke” to complete the magnetic flux return path. Yokeless architectures remove the stator back-iron entirely, leaving individual, isolated stator tooth segments.
- Advantage: Removing the stator iron yoke reduces stator mass by up to 80%, while increasing magnetic flux density across active copper coils. Flux lines travel directly from one rotor through the tooth segment to the opposing rotor.
- PCB (Printed Circuit Board) Stators:
- Mechanism: For low-to-medium power needs (such as robotics, light mobility, and drone propulsors), heavy copper wire is replaced by multi-layer copper traces etched directly onto FR4 or metal-core PCB discs.
- Advantage: Eliminates cogging torque, provides consistent geometric precision, allows automated surface-mount manufacturing, and creates a thin profile ($< 5\text{ mm}$ stator thickness).
Core Technology #2: Rotor Topology & Electromagnetic Design
The Core Challenge
Because axial flux rotors are flat discs placed close to stator faces, strong electromagnetic attraction forces (often exceeding thousands of Newtons) pull the rotor toward the stator. Furthermore, permanent magnets exposed to high-frequency rotational magnetic fields experience localized eddy current heating, risking magnet demagnetization.
Engineering Solutions:
- Dual-Rotor Topologies (Single Stator, Dual Rotor – SDR):
- Mechanism: A central stator disk sits sandwiched between two outer magnet rotor discs in a symmetrical sandwich layout.
- Advantage: The magnetic pull forces exerted by Rotor A on the stator are equal and opposite to those exerted by Rotor B. This balances axial forces, relieving the central bearing structure from massive continuous axial loads while doubling active torque surface area.
[ Rotor Disk 1 (Magnets N/S) ]
=== ------------------------------ === <-- Air Gap 1
[ Central Stator (SMC / Coils) ]
=== ------------------------------ === <-- Air Gap 2
[ Rotor Disk 2 (Magnets S/N) ]
- Halbach Array Magnet Configurations:
- Mechanism: Permanent magnets (typically High-Coercivity NdFeB or SmCo) are arranged in a spatially rotating magnetization pattern on the rotor surface.
- Advantage: Halbach arrays concentrate magnetic flux on the active air-gap side while cancelling the magnetic field on the back side. This removes the need for thick, heavy iron rotor backplates, lowering total rotor inertia.
- Magnet Segmentation & Skewing:
- Mechanism: Large permanent magnet blocks are divided into tiny, electrically isolated sub-segments (laminated magnets) and angled (skewed) across the radial vector.
- Advantage: Segmentation interrupts micro-eddy current loops, reducing internal magnet heating by up to 60%–70%. Magnet skewing smooths out field transitions, suppressing cogging torque and reducing Noise, Vibration, and Harshness (NVH).
Core Technology #3: Thermal Management & Precision Manufacturing
The Core Challenge
Generating high continuous power from a small package creates concentrated heat profiles. Standard external liquid cooling jackets (water-glycol rings) used around radial motors cannot properly cool axial flux stators, as heat must transfer radially through multiple thermal interfaces.
Engineering Solutions:
- Direct Immersion & Internal Channel Oil Cooling:
- Mechanism: Dielectric oil pumps directly into the stator core, submerging active copper windings or flowing through micro-channels etched within the SMC tooth structures.
- Advantage: Direct oil cooling removes heat directly from the point of origin. This lowers thermal resistance by over 3x, enabling the motor to operate continuously at $80\%-90\%$ of its peak rated output, whereas jacket-cooled motors degrade quickly under sustained loads.
- Micrometer Air-Gap Precision Control:
- Mechanism: Axial flux peak performance depends on maintaining a tight, uniform air gap (typically $0.5\text{ mm} – 1.2\text{ mm}$) between high-speed rotating rotor discs and the central stator face.
- Advantage: Automated assembly uses laser displacement sensors and active shimming during housing pressing to prevent disc tilt or thermal deformation under high torque loads.
- Automated Continuous Winding & Resin Potting:
- Mechanism: Robotic needle-winding machines wrap rectangular copper wire with high fill factors ($>65\%$). High-thermal-conductivity epoxy resins are thermally vacuum-potted around stator assemblies to fill air voids and transfer heat to housing structures.
4. Real-World Applications & Industry Landscape
The adoption of axial flux motors is expanding across high-demand mobility and industrial sectors:
1. Automotive & Supercars
- Mercedes-Benz / YASA: Mercedes acquired YASA to integrate axial flux motors into its upcoming AMG electric platform. The compact units fit on drive axles, delivering supercar acceleration with lower powertrain weight.
- Ferrari Plug-In Hybrids (SF90 / 296 GTB): Ferrari utilizes compact axial flux motors coupled between the internal combustion engine and gearbox to provide instant torque boost within tight spatial limits.
2. Aviation & Urban Air Mobility (eVTOL)
- Electric Aircraft Propulsors: Vertical takeoff aircraft (eVTOL) depend on strict weight limits. Axial flux motors provide the direct-drive torque needed to turn large propellers smoothly without heavy mechanical gearboxes.
3. Humanoid Robotics & High-Torque Actuators
- Direct-Drive Robotic Joints: Humanoid limbs require compact pancake actuators that fit within hip, knee, and shoulder joints, providing high hold-torque and smooth low-speed control without gear backlash.
5. Frequently Asked Questions (FAQ)
Q1: Why are axial flux motors more efficient than radial flux motors?
Answer: Axial flux motors feature shorter coil end-turns that directly cut copper resistance losses ($I^2R$). Additionally, the flat disc geometry offers a larger surface area for direct cooling, maintaining lower operating temperatures and preserving high electrical efficiency under load.
Q2: What is the primary manufacturing challenge in producing axial flux motors?
Answer: The primary bottleneck is managing heavy axial magnetic attraction forces while holding sub-millimeter air gap tolerances during high-volume assembly. Furthermore, manufacturing 3D stator cores requires specialized tooling, such as Soft Magnetic Composite (SMC) presses or specialized winding equipment.
Q3: What is the role of Soft Magnetic Composites (SMC) in axial flux motors?
Answer: SMC materials enable magnetic flux to flow freely in 3D (isotropically) because they consist of insulated iron powder particles. This allows engineers to press complex 3D stator tooth shapes with low eddy current losses at high operational frequencies.
Q4: Can axial flux motors operate without a gearbox in EVs?
Answer: Yes, axial flux motors deliver high low-end torque density, making them well suited for Direct-Drive powertrains. Removing the gearbox eliminates transmission weight, cuts mechanical friction losses, and simplifies overall drivetrain design.
6. Key Takeaways & Engineering Outlook
Electrification is shifting from basic capability to optimized efficiency and volumetric power density. While radial flux motors will continue to serve cost-sensitive, standard-performance applications, axial flux motors set the standard for high-performance, weight-critical, and space-constrained applications.
By combining Soft Magnetic Composite stators, dual-rotor Halbach topologies, and direct immersion oil cooling, axial flux technology has moved from a specialty concept into a prime power plant for next-generation mobility. Powertrain engineering teams that adopt axial flux architectures today will set the performance standards for tomorrow.
About the Author
Johnny Liu is the Chief Executive Officer at Dowway Vehicle. With extensive experience in advanced vehicle design, powertrain integration, and clean-energy mobility solutions, Johnny leads technical strategies focused on commercializing next-generation electric drivetrains and sustainable transport platforms.
For inquiries, technical collaborations, or engineering consultations regarding advanced motor integration, connect with Dowway Vehicle’s engineering team.