Axial flux motor
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An axial flux motor is an electric motor in which the magnetic flux crossing the gap between rotor and stator runs parallel to the shaft, rather than radiating outward from it as in a conventional motor. Standing the flux path on its end this way turns the motor into a flat disc instead of a cylinder, producing a "pancake" form factor that trades axial length for diameter. Because the torque-producing air gap in this layout is an annular disc rather than a tube, torque grows roughly with the cube of the rotor's diameter instead of the square, which is why axial flux designs can pack unusually high torque into a short package.[1][2] That property has pulled axial flux motors into performance cars, light aircraft, and, increasingly, the compact high-torque joints of legged and humanoid robots.[2][3]
In plain terms: most electric motors are built like a tube, with a ring of magnets spinning inside or around a ring of copper windings, the way one can rotates inside a slightly larger can. An axial flux motor is built more like two dinner plates facing each other a few millimeters apart, one carrying magnets and the other flat coils, spinning around a shaft that runs through the middle of both. The dinner-plate shape is what lets the motor be wide and short instead of narrow and long.
How it works: radial, axial, and transverse flux
Three geometries describe where a motor's magnetic flux travels relative to its rotating shaft.[1][3]
In a radial flux motor, flux crosses the air gap perpendicular to the shaft, moving outward from the rotor to the stator, or the reverse in an outrunner design. This is the shape of most electric motors built since the 19th century: a cylindrical rotor spinning inside, or around, a cylindrical stator. Radial flux motors can be made long and thin or short and fat simply by changing the length of the stack of steel laminations, which is one reason the design has scaled so easily across such a wide range of sizes and applications.[3]
In an axial flux motor, flux crosses the gap parallel to the shaft, and the rotor and stator are flat discs facing each other rather than nested tubes. The active magnetic surface is an annulus whose area grows with the square of the diameter, and that material also sits farther from the shaft, a longer lever arm, as the disc gets bigger, so torque output grows close to the cube of the diameter.[1][2] A wide, short axial flux motor can out-torque a longer, narrower radial flux motor of similar weight, and the flat shape exposes more surface area for cooling per unit of volume than a cylinder of equal weight.[1]
In a transverse flux motor, flux forms closed loops that lie in planes transverse, or perpendicular, to the direction of rotation, typically through U-shaped iron cores wrapped around each pole. This decouples the electrical and magnetic circuits in a way radial and axial designs cannot, which allows very high pole counts and, in principle, the highest torque density of the three geometries at low speed. In practice, transverse flux motors have stayed mostly in the laboratory and in a handful of direct-drive generator and in-wheel motor prototypes, held back by complex three-dimensional flux paths, poor power factor, and high manufacturing cost.[4]
| Property | Radial flux | Axial flux | Transverse flux |
|---|---|---|---|
| Flux direction | Perpendicular to the shaft | Parallel to the shaft | Perpendicular to the direction of rotation, in loops around each pole |
| Typical shape | Cylindrical | Flat disc, or "pancake" | Ring-shaped, often large diameter |
| Torque versus diameter | Roughly diameter squared | Roughly diameter cubed | Set largely by pole count, decoupled from winding layout |
| Manufacturing maturity | High: decades of tooling for stacked steel laminations | Moderate: needs wound tape cores, powder metal, or PCB stators with tight, flat air gaps | Low: complex 3D flux paths usually need soft magnetic composite cores |
| Where it dominates | Nearly all industrial motors, most EV traction motors, most robot joints today | Performance EV motors, light aircraft, in-wheel motors, emerging robot joints | Direct-drive wind generators and in-wheel concepts, mostly prototypes |
Topologies and variants
Within the axial flux family, designers choose how many rotor and stator discs to stack and whether to keep the stator's iron yoke.[1][5]
| Topology | Arrangement | Key trait | Example makers |
|---|---|---|---|
| Single stator, single rotor | One stator disc, one rotor disc | Simplest and cheapest to build, but the rotor and stator pull toward each other with a large, unbalanced axial force that the bearings and housing alone must resist | Common in small prototype and hobbyist motors |
| Single stator, dual rotor (yokeless) | One stator disc sandwiched between two rotor discs | Axial pull from the two rotors cancels out. Removing the stator's iron yoke, the arrangement behind the name "Yokeless and Segmented Armature", cuts weight and core loss, but leaves each tooth segment needing its own mechanical support and cooling path | YASA, Magnax |
| Dual stator, single rotor | One rotor disc sandwiched between two stator discs | Also balances axial forces. Because each stator disc can bolt directly to the housing, heat generally has an easier path out than in the yokeless design | Whylot, Turntide, Infinitum Electric |
| Multi-stage or stacked | Multiple rotor-stator pairs sharing one shaft | Adds power by adding stages along the shaft rather than by growing diameter | YASA (750R), Emrax |
| Ironless or coreless stator | Rotor(s) as above, but the stator has no iron teeth, only windings or circuit-board traces | Nearly eliminates cogging torque and stator core losses; widens the air gap and lowers torque density compared with an iron-cored design of the same size | Infinitum Electric and academic prototypes |
Removing the stator's iron creates its own problems. Without a shared iron ring, individual tooth segments in a yokeless stator need their own mechanical support, and heat has fewer paths out.[6] A 2025 printed-circuit-board motor for small robots, developed by researchers at Carnegie Mellon University's Robotics Institute working with the motor maker Microbot Motor, uses the dual-stator, coreless approach: a 48-layer stator built from four 12-layer PCB modules using high-density-interconnect manufacturing, with a single rotor disc sandwiched in between and the whole assembly only 19 millimeters across and 5 millimeters thick.[2] Prototype ironless axial flux machines elsewhere have reported efficiencies above 98 percent, since removing the iron removes hysteresis and eddy-current core losses along with most of the cogging torque.[7][2]
Torque density, power density, and cooling
The headline argument for axial flux motors is torque and power per kilogram. YASA's 750R, a stackable automotive unit, weighs 37 kilograms and delivers 800 newton-meters of torque at more than 5 kilowatts per kilogram, in an axial length of 98 millimeters.[1] In July 2025 YASA said a prototype motor weighing 13.1 kilograms had produced 550 kilowatts, a power density of about 42 kilowatts per kilogram that the company described as the highest yet achieved for an electric motor of any kind.[1] Emrax's aviation and motorsport motors reach roughly 4.6 to 5 kilowatts per kilogram depending on the model,[8] and Turntide's industrial AF430S is rated at more than 96 percent efficiency with over 20.5 newton-meters of torque per kilogram.[9] These are manufacturer datasheet figures gathered under different test conditions and are not strictly comparable to one another, but they consistently land well above typical radial flux motors of similar weight.
McLaren's own comparison of its Artura hybrid motor to the older, radial flux motor in the McLaren P1 makes the case concretely. The Artura's axial flux motor, supplied by YASA, reaches about 4.6 kilowatts per kilogram, which McLaren describes as 33 percent higher power density than the P1's motor, while weighing under half as much: about 15.4 kilograms against roughly 38 kilograms for the P1 unit.[10]
The flat geometry also exposes more surface area to the air or a cooling jacket for a given motor volume than a cylindrical radial flux motor of the same weight.[1] In practice, cooling an axial flux motor is harder than that surface-area argument suggests, for reasons the next section covers.
Manufacturing and thermal challenges
Axial flux motors remain more expensive and less standardized to build than radial flux motors, for a few related reasons.
A radial flux stator is built from identical stacked steel laminations, a manufacturing process refined over more than a century. An axial flux stator's laminations, wound tape cores, or powder-metal segments are wedge-shaped and vary across their radius, which is harder to stamp, wind, or mold consistently at volume.[11][6]
Because the entire torque-producing surface sits at a large diameter, an axial flux motor's air gap has to stay uniform across the whole disc, often to a fraction of a millimeter, even as the rotor and stator heat up and expand at different rates. Radial flux motors face a version of the same problem, but over a much smaller diameter.[11]
The magnets and stator also pull toward each other along the axis with considerable force, which a single-air-gap design must resist entirely through its bearings and housing. Dual-rotor and dual-stator designs cancel most of this force between the two sides, which is a large part of why those topologies dominate commercial axial flux motors despite being harder to assemble than a single stator and rotor.[1][6]
Heat extraction is also uneven across topologies. In the yokeless, single-stator designs used by YASA and Magnax, the stator sits between two rotors with no direct, solid path to an outer housing on either face, so heat has to travel out through the stator's edge or through cooling channels built into the stator itself. Dual-stator designs, where the stator discs mount directly to the housing, generally have an easier time shedding heat for that reason, at the cost of a second air gap to hold in tolerance.[6][11]
None of this has stopped the technology from reaching production, but it explains why axial flux motors, decades after the basic principle was understood, are only now moving from motorsport and boutique electric vehicles into mass manufacturing.
Adoption in electric vehicles and aviation
Axial flux motors have found their earliest volume market in performance and hybrid vehicles, where light weight and short axial length matter more than the cost premium over a mature radial flux design.
YASA, an Oxford spinout founded in 2009 by Malcolm McCulloch and Tim Woolmer, takes its name from "Yokeless and Segmented Armature."[12] Its motors have powered the Koenigsegg Regera hypercar, where two direct-drive YASA 750 motors (a combined 1,600 newton-meters and 360 kilowatts) drive the rear axle and a third YASA unit works as a motor-generator, all part of Koenigsegg's transmission-less "Direct Drive" system.[13] YASA motors have since appeared in the Ferrari SF90 Stradale and 296 GTB, the Lamborghini Revuelto, and the McLaren Artura, where a 15.4-kilogram, 225-newton-meter motor supplies instant "torque infill" while the Artura's twin-turbo V6 spools up.[1][10] Mercedes-Benz acquired YASA outright in July 2021,[14] and in June 2026 began large-scale production of its own axial flux motor at its Berlin-Marienfelde plant, across seven new production lines. The motor's first application is the Mercedes-AMG GT 4-Door Coupe, whose three axial flux units together deliver up to 860 kilowatts of peak output.[15][16]
Koenigsegg is a more complicated case than it first appears. Its Regera used YASA-supplied axial flux motors, but the motor in its newer Gemera grand tourer, called Quark, is an in-house design that Koenigsegg calls "Raxial Flux," a deliberate hybrid of radial and axial flux geometry rather than a pure axial flux machine. Quark weighs about 30 kilograms and produces up to 600 newton-meters of torque and 250 kilowatts, packaged into the "Terrier" drive unit alongside Koenigsegg's own inverter.[17][18]
Whylot, a French motor developer founded in 2011 in the Lot department, builds dual-stator axial flux motors and has filed dozens of patents on the design. Renault Group took a 21 percent stake in Whylot in late 2021 after an earlier development partnership, aiming to be the first mainstream automaker to build axial flux motors at scale.[19] Whylot moved from prototyping to small-scale production around 2024, and Renault has said the performance-oriented Renault 5 Turbo 3E will use axial flux motors on its rear axle starting in 2027, contributing to a peak system output of 400 kilowatts.[20]
Outside road vehicles, axial flux motors set an aviation record in November 2021, when Rolls-Royce's "Spirit of Innovation" test aircraft, powered by three YASA motors each producing 790 newton-meters and 200 kilowatts, reached 555.9 kilometers per hour (345.4 mph) over a 3-kilometer course, at the time the fastest verified speed for an all-electric aircraft.[21][22] Evolito, a YASA spinout founded by Tim Woolmer in 2021, now develops axial flux motors specifically for aircraft and airships, building on that lineage.[23]
Use in robotics and humanoid-robot joints
A humanoid robot's joint has to fit inside a compact, roughly disc-shaped envelope, wide but shallow, and produce high torque at low speed, which is close to a description of what an axial flux motor is good at.[2] That has made the topology a subject of active research for quasi-direct drive joint actuators, a design approach that pairs a torque-dense motor with a low or no gear reduction, often a single stage rather than the 100:1 or higher ratios used with a harmonic drive, to preserve backdrivability and fine force control rather than maximizing raw torque through gearing alone.[2]
Academic prototypes illustrate the appeal. The Carnegie Mellon University and Microbot Motor design described above reported a stator copper fill of 45 percent, which its authors described as a record for the format, and said the thin, disc-shaped geometry "fits easily inside robot joints and simplifies heat extraction" compared with a cylindrical motor of equivalent torque.[2] A separate actuator design for biped robot joints, presented at the 2023 Intelligent Robotics and Applications conference, pairs a 12.5-newton-meter axial flux motor with a two-stage planetary gear train reduction of about 16 to 1 to reach the torque needed for walking while keeping weight and volume low.[24]
Commercial adoption in robotics so far sits mostly in industrial and collaborative arms rather than humanoids. Turntide Technologies markets its dual-stator axial flux motors, including the AF300 and AF400 families, for uses that include industrial robots alongside construction machinery, marine propulsion, and fans and pumps, citing 30 to 40 percent higher torque than equivalent radial flux motors in the same envelope.[9] The wider humanoid robot industry that scaled rapidly from 2023 onward, with programs at companies including Tesla Optimus, Figure AI, Unitree, and 1X Technologies, has renewed engineering interest in axial flux joint motors for the reasons above. As of mid-2026, however, no major humanoid robot developer has publicly confirmed shipping axial flux motors in a production humanoid robot's joints. Most disclosed humanoid actuator designs still use conventional radial flux frameless motors paired with harmonic or cycloidal drive reducers, and axial flux so far remains concentrated in academic prototypes, component suppliers, and adjacent industrial robotics rather than in shipped humanoid hardware.[2][6]
Axial flux motors are, at the physical level, still permanent-magnet brushless DC motors. The same three-phase electronic commutation used in cylindrical robot actuators applies directly to a disc-shaped one, and a rotary encoder mounted on the shaft closes the position loop the same way it would on a radial flux servo motor. What changes is the mechanical arrangement of magnets and windings, not the control electronics.[3]
Suppliers and landscape
| Company | Country | Topology focus | Notable applications |
|---|---|---|---|
| YASA (Mercedes-Benz subsidiary) | United Kingdom | Single stator, dual rotor, yokeless | Koenigsegg Regera, Ferrari SF90/296, Lamborghini Revuelto, McLaren Artura, Mercedes-AMG GT 4-Door Coupe[13][10][16] |
| Evolito | United Kingdom | Single stator, dual rotor, YASA-derived | eVTOL aircraft and airship propulsion; spun out of YASA's aerospace unit in 2021[23] |
| Magnax | Belgium | Single stator, dual rotor, yokeless | Vehicle and industrial motors; raised 35.5 million euros from Pan-International Industrial Corp and Foxconn Group in April 2026 to scale production[25] |
| Whylot | France | Dual stator, single rotor | Renault Group hybrid and EV powertrains; 21 percent owned by Renault since 2021[19][20] |
| Emrax | Slovenia | Stacked disc, single stator and rotor pairs | Light aircraft, including the EASA-certified EMRAX 268, plus motorsport and marine motors[8] |
| Saietta | United Kingdom and India | Axial Flux Technology (AFT) motors | Two- and three-wheeler EVs, manufactured in Sunderland, UK, and Manesar, India, through the Saietta VNA joint venture[26] |
| Infinitum Electric | United States | Dual stator, single rotor, PCB stator | Industrial HVAC, pump, and data-center motors, plus an EV and mobility product line[27] |
| Turntide Technologies | United States | Dual stator, single rotor | Industrial robots, construction and marine equipment, fans, and pumps[9] |
| Koenigsegg | Sweden | In-house hybrid "Raxial Flux" | Quark motor and Terrier drive unit for the Gemera grand tourer[17][18] |
| Mercedes-Benz / Mercedes-AMG | Germany | Single stator, dual rotor, YASA-derived | In-house production since June 2026 at Berlin-Marienfelde, for AMG.EA high-performance EVs[15][16] |
See also
- Brushless DC motor
- Coreless motor
- Servo motor
- Actuator
- Quasi-direct drive
- Harmonic drive
- Cycloidal drive
- Planetary gear train
- Humanoid robots
References
- Wikipedia, "Axial flux motor," https://en.wikipedia.org/wiki/Axial_flux_motor ↩
- Wang, J., Xie, Q., Han, J., Zhang, Y., Atkeson, C., Gupta, A., Pathak, D., and Bisk, Y., "High Torque Density PCB Axial Flux Permanent Magnet Motor for Micro Robots," arXiv:2509.23561, September 2025, https://arxiv.org/abs/2509.23561 ↩
- "What's the Difference Between Axial- and Radial-Flux Electric Motors?", Electronic Design, https://www.electronicdesign.com/technologies/power/article/21276212/ecm-pcb-stator-tech-whats-the-difference-between-axial-and-radial-flux-electric-motors ↩
- "A Review of Transverse Flux Machines Topologies and Design," Energies (MDPI), vol. 14, no. 21, article 7173, https://www.mdpi.com/1996-1073/14/21/7173 ↩
- "Comprehensive Analysis of Dual-Rotor Yokeless Axial-Flux Motor with Surface-Mounted and Halbach Permanent Magnet Array for Urban Air Mobility," Energies (MDPI), vol. 17, no. 1, article 30, https://www.mdpi.com/1996-1073/17/1/30 ↩
- "Axial flux motors," E-Mobility Engineering, https://www.emobility-engineering.com/axial-flux-motors/ ↩
- "Analysis and Implementation of New Ironless Stator Axial-Flux Permanent Magnet Machine With Concentrated Nonoverlapping Windings," ResearchGate, https://www.researchgate.net/publication/322811026 ↩
- Emrax, company overview and motor specifications, https://en.wikipedia.org/wiki/Emrax and https://emrax.com/ ↩
- Turntide Technologies, axial flux motor product line, https://turntide.com/products/motors/; "Turntide Expands Axial Flux Motor Portfolio," GlobeNewswire, April 2026, https://www.globenewswire.com/news-release/2026/04/22/3278690/0/en/turntide-expands-axial-flux-motor-portfolio-offering-more-solutions-in-a-compact-footprint-for-hybrid-electric-systems.html ↩
- "Tech Insider: McLaren Artura," Automotive Powertrain Technology International, https://www.automotivepowertraintechnologyinternational.com/features/tech-insider-mclaren-artura.html ↩
- "Axial Flux Motor Design Solutions for Loss Reduction, Cooling Enhancement, and Manufacturability Improvement," SAE Technical Paper 2026-01-5001, SAE Mobilus, https://saemobilus.sae.org/papers/axial-flux-motor-design-solutions-loss-reduction-cooling-enhancement-manufacturability-improvement-2026-01-5001 ↩
- Wikipedia, "YASA Limited," https://en.wikipedia.org/wiki/YASA_Limited ↩
- YASA Limited, "Koenigsegg Regera, A 1500hp Hybrid Megacar," https://yasa.com/applications/koenigsegg/ ↩
- "Acquired by Mercedes-Benz, YASA's revolutionary electric motor is set for big things," TechCrunch, September 2021, https://techcrunch.com/2021/09/03/acquired-by-mercedes-benz-yasas-revolutionary-electric-motor-is-set-for-big-things/ ↩
- Mercedes-Benz Group, "Large-scale production of electric axial flux motor," June 2026, https://group.mercedes-benz.com/company/production/news/axial-flux-motor-berlin.html ↩
- "Mercedes-Benz begins axial flux motor production in Berlin," Electrive, June 2026, https://www.electrive.com/2026/06/10/mercedes-benz-begins-axial-flux-motor-production-in-berlin/ ↩
- "Koenigsegg Explains How It Created the Raxial-Flux Motor," autoevolution, https://www.autoevolution.com/news/koenigsegg-explains-how-it-created-the-raxial-flux-motor-180689.html ↩
- Koenigsegg, "Quark E-motor," https://www.koenigsegg.com/quark-emotor ↩
- "Renault Group takes 21% stake in axial flux e-motor company Whylot," Green Car Congress, November 2021, https://www.greencarcongress.com/2021/11/20211124-whylot.html ↩
- "Le rotor de notre moteur a flux axial condense 10 ans de recherche, souligne Romain Ravaud de Whylot," Usine Nouvelle, https://www.usinenouvelle.com/article/le-rotor-de-notre-moteur-a-flux-axial-condense-10-ans-de-recherche-souligne-romain-ravaud-de-whylot.N1805777 ↩
- Rolls-Royce, "The Spirit of Innovation officially breaks speed record and becomes the world's fastest all-electric vehicle," January 2022, https://www.rolls-royce.com/media/press-releases/2022/20-01-2022-the-spirit-of-innovation-officially-breaks-speed-record.aspx ↩
- YASA Limited, "ACCEL, The Spirit of Innovation," https://yasa.com/applications/spirit-of-innovation/ ↩
- "Telling the founder story of Dr Tim Woolmer, YASA Motors founder and CTO and Evolito director," eVTOL Insights, https://evtolinsights.com/video-telling-the-founder-story-of-dr-tim-woolmer-yasa-motors-founder-and-cto-and-evolito-director/ ↩
- "Design of an Actuator for Biped Robots Based on the Axial Flux Motor," Intelligent Robotics and Applications (2023), https://www.researchgate.net/publication/374749181_Design_of_an_Actuator_for_Biped_Robots_Based_on_the_Axial_Flux_Motor ↩
- "Belgium's Magnax secures 35.5 million euros with Foxconn backing to industrialise axial flux motor technology," EU-Startups, April 2026, https://www.eu-startups.com/2026/04/belgiums-magnax-secures-e35-5-million-with-foxconn-backing-to-industrialise-axial-flux-motor-technology/ ↩
- "Saietta VNA commences axial-flux e-motor production at Manesar plant," Autocar Professional, https://www.autocarpro.in/news-national/saietta-vna-commences-axial-flux-e-motor-production-at-manesar-plant-118297 ↩
- "Axial Flux Motor Topology Signals Next Generation of Electric Motors," Machine Design, https://www.machinedesign.com/mechanical-motion-systems/article/21281110/infinitum-axial-flux-motor-topology-signals-next-generation-of-electric-motors ↩
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