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The name usually refers to a yokeless axial-flux permanent-magnet motor: instead of putting a cylindrical rotor inside a surrounding stator, it uses flat rotor discs on either side of a stator. In the Magnax and YASA-style arrangement, the stator has windings on segmented teeth but no conventional cylindrical back-iron yoke. The result can be a shorter, lighter motor with two active air gaps, making it attractive for high-performance EVs and other space-constrained vehicles.
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That does not make axial flux an automatic replacement for the mature radial-flux motors used in most EVs. Cooling, manufacturing, axial-force control, noise and vibration, magnet cost, and supply-chain scale still determine whether the design wins in a particular vehicle.
What makes an EV motor “inside out”?
Most electric traction motors in cars use a radial-flux layout. Picture a metal cylinder: the rotor spins in the middle, the stator surrounds it, and magnetic flux crosses the air gap from the rotor toward the stator in a radial direction. The stator’s iron then provides a return path for the magnetic field.
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An axial-flux motor changes the orientation. Its rotor is shaped more like a disc, the stator is comparatively flat, and the magnetic flux crosses the air gap along the motor’s axis—the same direction as the shaft. “Inside-out” is a useful visual description, not a formal engineering category.
| Feature | Typical radial-flux motor | Yokeless axial-flux motor |
|---|---|---|
| Overall shape | Cylindrical | Flat or pancake-like |
| Rotor arrangement | Usually one rotor inside a surrounding stator | Often two disc rotors bracketing one stator |
| Direction of flux across the air gap | Radial | Axial |
| Stator structure | Usually includes a continuous back-iron yoke | Yokeless designs use separate stator teeth or segments |
| Main packaging advantage | Long-established cylindrical envelope | Potentially much shorter axial length and high output per mass or volume |
| Main industrial advantage | Mature manufacturing, supply chain, and vehicle integration | Potentially better power density, but more demanding assembly and thermal design |
Not every axial-flux motor is yokeless, and not every yokeless design uses exactly the same magnetic circuit. The architecture discussed here is the double-rotor, single-stator configuration associated with Magnax and YASA, sometimes described as a yokeless and segmented armature.
How the two-rotor design produces more from less
In a double-rotor axial-flux machine, the stator sits between two permanent-magnet rotors. Both faces of the stator interact with a rotor, creating two active air gaps rather than one. The arrangement can also help balance the axial magnetic forces that would otherwise pull a single rotor toward one side of the stator.
The stator teeth carry the copper windings and concentrate the magnetic field where it produces torque. A conventional motor would connect those teeth with a cylindrical ring of back iron—the stator yoke. In the yokeless design, the segments are not joined by that continuous ring. The magnetic path is therefore shorter and contains less inactive iron.
That missing yoke is the central claim behind the Magnax approach. In the comparison described in a 2019 IEEE Spectrum feature, the yoke represented roughly two-thirds of the stator iron. Removing it reduced mass and iron losses in the company’s design. Magnax also discussed grain-oriented electrical steel, whose magnetic properties are especially useful when the flux follows a more controlled direction; the company reported an 85 percent reduction in flux losses in the relevant iron comparison.
Those figures describe a particular design and material comparison. They are not properties that every axial-flux motor automatically inherits. The gains depend on how the magnetic field travels, the grade and orientation of the electrical steel, the air-gap geometry, the winding design, and how much structural material is needed to keep the rotors accurately aligned.
Why power density matters in an electric car
Power density is output divided by mass or volume. A motor rated at 100 kW that weighs 100 kg has a mass power density of 1 kW/kg. Torque density applies the same idea to torque, usually in newton-metres per kilogram or per litre.
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- Less mass: a lighter drive unit can reduce the vehicle’s total mass and the energy needed to accelerate it.
- More packaging freedom: a shorter motor can leave room for suspension components, battery structure, crash protection, or a lower vehicle floor.
- More motors without as much penalty: a performance EV can use two, three, or four drive units while limiting the added drivetrain mass.
- Higher output in a fixed envelope: the same installation space may support more peak power or torque.
The benefit is most compelling when installation length is restricted or when the vehicle needs very high output. That is why axial flux is being explored for performance cars, motorcycles, aircraft, compact commercial vehicles, and some in-wheel or near-wheel concepts.
It is important not to turn power density into a guaranteed range improvement. Range also depends on the battery, inverter, gearing, tires, aerodynamics, software, duty cycle, and thermal system. A lighter motor may help, but a company’s projected range gain is not the same thing as an independently measured vehicle result. The advantage can multiply in a multi-motor vehicle, but that remains an application calculation rather than a universal fleet result.
The headline numbers—and what they actually prove
The original Magnax story included unusually strong prototype and design figures:
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- University of Ghent testing reportedly measured prototype efficiencies between 91 and 96 percent.
- The design’s peak power density was reported at approximately 15 kW/kg.
- The comparison cited a BMW i3 motor at approximately 3 kW/kg.
These are historical figures from the 2019 report, and the 15 kW/kg number was a design peak rather than a universal sustained rating. It should not be read as meaning that every axial-flux motor produces five times the power density of every radial-flux motor.
Magnax later described its Traxial ground-mobility design as offering up to three times the torque density and up to twice the power density of existing EV motors, with an axial length around one-third that of a typical radial-flux design. Those are Magnax claims about its own design. Direct oil cooling between the windings and along the sides of the stator core is part of the company’s effort to make that compact package manufacturable and thermally viable.
The more defensible conclusion is that the topology has a credible route to unusually high power density—not that a single headline number is representative of the entire industry.
What changed from an interesting prototype to a practical technology?
The strongest evidence of progress is not one efficiency figure. It is that major vehicle companies and suppliers are now working through the problems that appear when the motor has to survive real production, duty cycles, vibration, temperature swings, cost targets, and service requirements.
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YASA’s name comes from Yokeless and Segmented Armature, the architecture at the centre of its business. YASA is a wholly owned Mercedes-Benz subsidiary.
In its official AMG.EA material, Mercedes-Benz says the rear axle of its high-performance vehicle program uses two oil-cooled axial-flux motors developed with YASA. Mercedes describes the architecture as approximately three times as power dense as conventional electric motors while occupying roughly one-third of the installation space.
That is meaningful evidence that axial flux has moved beyond a university demonstration. Mercedes-AMG has been working with YASA to elevate the technology toward series production, and the program demonstrates that a major automaker considers the packaging and performance benefits worth integrating into a vehicle platform.
It still does not mean that every Mercedes EV uses an axial-flux motor, or that the architecture is already common in mainstream cars. The claim belongs specifically to the AMG.EA program and to Mercedes-Benz’s stated comparison. The relevant distinction is between production-oriented deployment and mass-market standardization.
Magnax is adapting the platform to different markets
Magnax’s current corporate structure also shows why there may not be one universal axial-flux motor. Its ground-e-mobility business is identified as Traxial, while Axyal is focused on aerospace.
Those markets value different things. A ground vehicle may prioritize crash robustness, cost, cooling, and high-volume assembly. An aircraft may place greater value on mass, redundancy, continuous power, and certification. A motor designed for one market cannot simply be assumed to satisfy the other.
The practical obstacles are the real test
1. Heat removal is harder in a pancake motor
Electric motors lose energy as heat in the copper windings, magnetic material, electrical steel, bearings, and power electronics. A motor can have excellent peak figures and still be unsuitable if it cannot continuously reject heat.
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The axial-flux arrangement makes that difficult because the stator is trapped between two rotors. The compact geometry leaves less obvious room for a conventional cooling jacket, and the hottest parts of the winding and core may be difficult to reach without adding channels, fins, or direct oil flow.
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A GM research team’s 2026 SAE paper identifies thermal management as one of the major axial-flux challenges. The work examined stator cooling fins and direct air-gap oil cooling. In the tested design, the cooling-fin approach reduced core temperature by a reported 15 °C. The study also reported only 0.3 N·m of drag torque above 500 rpm for a low-temperature permanent-magnet configuration under its tested conditions.
Those results show the kind of engineering progress required, but they are not guarantees for every motor. Oil flow rate, oil temperature, rotor speed, seal design, winding insulation, and the vehicle’s overall thermal loop all change the result. Direct oil cooling can improve heat transfer while adding pumps, passages, seals, contamination concerns, and manufacturing steps.
2. The stator is compact but not necessarily simple
Axial-flux stators commonly use segmented or trapezoidal laminations. That geometry makes it possible to place material where it helps the magnetic circuit, but it complicates production compared with familiar radial-flux laminations.
The GM SAE study describes the need to assemble hundreds of laminations of varying sizes as a manufacturing difficulty. It investigated a hybrid stator-core approach intended to reduce that complexity and reported a simulated and experimentally evaluated peak efficiency of 96.5 percent for the optimized design.
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Production also has to hold the two rotors parallel to the stator with a very small, consistent air gap. Any tilt, deflection, or uneven assembly can increase losses, create uneven magnetic forces, produce vibration, or cause physical contact. The design may save stator iron while demanding more precision in fixtures, rotor carriers, bearings, adhesives, winding, and end-of-line inspection.
3. Axial forces create a different NVH problem
Noise, vibration, and harshness—usually abbreviated NVH—are not just comfort issues. Unwanted vibration can shorten bearing life, stress the housing, excite body panels, and make a premium vehicle feel unfinished.
The flat geometry and high axial magnetic forces introduce different structural and torque-ripple behaviour from a conventional radial-flux machine. A 2025 GM-led SAE study described NVH as a major challenge in an axial-flux prototype rated at 320 N·m of peak torque and 140 kW of peak power.
A separate 2025 Mercedes-Benz and TU Darmstadt SAE paper examined rotor skewing and segmented permanent magnets as ways to reduce dominant torque-ripple harmonics across the torque-speed range. The existence of this work is significant: NVH is an active design target, not evidence that every axial-flux motor is inherently noisy.
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The trade-off is that a feature that improves one metric can hurt another. Skewing can reduce a harmonic while affecting torque density, manufacturing complexity, or loss. Segmented magnets can enable better electromagnetic control but require more parts and assembly operations.
4. Materials and the supply chain still matter
A high-performance motor needs more than a clever flux path. Its cost and availability depend on permanent magnets, electrical steel, copper, precision bearings, structural rotor parts, cooling hardware, insulation, winding equipment, and the inverter that drives it.
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Yokeless designs still use permanent magnets in the Magnax and YASA examples. They do not eliminate rare-earth material requirements. Magnet-free motors are a separate branch of electric-machine design and should not be treated as a built-in benefit of axial flux.
The use of grain-oriented electrical steel may reduce losses in a flux path that is strongly directional, as Magnax reported, but specialized material can also create sourcing and processing requirements. A material advantage is valuable only if it remains economical and consistent at production volumes.
Axial flux versus the incumbent radial-flux motor
Axial flux is competing with a technology that is already very good. The U.S. Department of Energy describes internal permanent-magnet motors as offering high power density and high efficiency over a broad operating range. Radial-flux IPM motors also benefit from mature laminations, automated winding, established suppliers, extensive durability data, familiar inverters, and vehicle integration experience.
| Question | Axial flux may have the edge when… | Radial flux may remain the better choice when… |
|---|---|---|
| Packaging | The vehicle needs a short motor or a large amount of output in a constrained space. | A conventional cylindrical motor already fits the platform efficiently. |
| Performance | Peak power, torque density, and low mass are worth additional cost and complexity. | The vehicle has moderate output requirements and values proven durability and price. |
| Production volume | The program can justify specialized tooling and precision assembly. | The vehicle is a high-volume model that depends on an established supply chain. |
| Thermal system | Direct oil cooling and a custom thermal loop can be integrated from the start. | The platform is already optimized around a conventional cooling system. |
| NVH development | The manufacturer has the analysis, testing, and structural control needed to manage axial forces and torque ripple. | Low development risk and a large body of existing NVH knowledge are priorities. |
In other words, the question is not whether axial flux is theoretically more efficient. It is whether its system-level advantage survives the complete vehicle design.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Where the design makes the most sense
High-performance EVs
Performance vehicles are a natural first market. They can justify expensive technology if it delivers more acceleration, a smaller drive unit, or room for additional motors. A lighter motor also helps offset the mass of a large battery, although the final benefit depends on the whole drivetrain.
Motorcycles and compact vehicles
Two-wheelers and small vehicles often have severe packaging constraints. A short axial motor can fit where a long cylindrical unit cannot. Cooling, sealing, cost, and durability are still critical, particularly because motorcycles expose the motor to weather and may have less thermal capacity than a car.
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Aerospace places an unusually high value on mass and power density, which explains Magnax’s separate Axyal aerospace focus. Certification, redundancy, continuous-power capability, electromagnetic compatibility, and fault tolerance are demanding requirements, however. A promising motor figure alone does not make an aircraft propulsion system ready for service.
In-wheel and near-wheel drives
The short axial dimension can make axial flux attractive for in-wheel or near-wheel packaging. But a motor placed in the wheel adds unsprung mass, which can hurt suspension response and ride. It also faces difficult sealing, cooling, impact, bearing, and durability requirements. A compact motor does not automatically make a good in-wheel motor.
Mainstream family EVs
Axial flux could eventually appear in higher-volume vehicles, but this is where the incumbent has its greatest advantages. If a radial-flux motor already meets the vehicle’s power, efficiency, packaging, cost, and durability targets, switching architectures may offer too little benefit to justify the risk.
What “practical” should mean here
There are several different meanings of practical, and axial flux does not reach them all at once:
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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11- Technically practical: yes. Working prototypes and independently studied designs demonstrate that the magnetic and thermal problems can be engineered.
- Commercially practical: yes, for selected applications. YASA’s Mercedes-AMG program and Magnax’s market-specific Traxial and Axyal businesses show serious commercial intent.
- Ready for widespread mass-market use: not proven. Production scale, cost, serviceability, long-term durability, and supply-chain economics still have to be demonstrated across large vehicle volumes.
- Universally superior: no. The best motor depends on the duty cycle, cooling architecture, inverter, battery, packaging envelope, manufacturing scale, and vehicle target.
This distinction also explains why the technology can be both genuinely practical and not yet commonplace. An architecture can be ready for a premium performance axle while remaining the wrong economic choice for a high-volume commuter EV.
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Verdict
The inside-out EV motor has earned a place in serious vehicle engineering. Its double-rotor, yokeless axial-flux layout can reduce inactive iron, use two active air gaps, shorten the motor, and deliver exceptional output for its mass or volume. Historical Magnax prototypes, later company designs, Mercedes-AMG’s YASA-based program, and current SAE research all support the view that this is more than a laboratory curiosity.
But the headline advantage is conditional. The same compact geometry complicates heat removal, segmented-stator manufacture, rotor alignment, axial-force control, and NVH tuning. The strongest published power-density numbers are design-specific or company-reported, not universal benchmarks. And conventional radial-flux IPM motors remain highly competitive because they are mature, efficient, scalable, and well understood.
So the accurate answer is: axial flux is finally practical where power density and packaging are worth paying for—especially premium performance and specialized EVs—but it has not yet displaced radial flux as the default motor for the car industry.
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Are all axial-flux motors yokeless?
No. Axial flux describes the direction of the magnetic flux and the motor’s disc-like arrangement. Some axial-flux motors can retain a stator yoke. The yokeless, segmented-stator design is one particular implementation associated with companies such as Magnax and YASA.
Does an axial-flux motor eliminate rare-earth magnets?
No. The Magnax and YASA designs discussed here use permanent magnets. A magnet-free motor may avoid rare-earth materials, but that is a separate design choice rather than an automatic benefit of axial flux.
Is 15 kW/kg a normal axial-flux motor rating?
No. The approximately 15 kW/kg figure came from a historical Magnax design peak reported in 2019. It is not a universal or necessarily continuous rating for axial-flux motors.
Are all Mercedes-Benz electric cars switching to axial-flux motors?
No. Mercedes-Benz’s official material identifies two YASA-developed, oil-cooled axial-flux motors for the rear axle of its AMG.EA high-performance vehicle program. That is production-oriented evidence for a specific program, not proof that every Mercedes EV uses the architecture.
Will axial flux give an EV more driving range?
It can help indirectly by reducing motor mass and freeing packaging space, particularly in a multi-motor vehicle. However, range depends on the entire vehicle, and company-projected range benefits should not be presented as independently measured improvements.
The Bottom Line
Bottom line: the yokeless axial-flux motor is no longer just an intriguing prototype. It is a credible production technology for premium performance and specialized EV applications, but cooling, manufacturing, NVH, cost, and scale keep conventional radial-flux motors firmly in charge of the mainstream.
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