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Continuous torque—not the biggest short-duration peak—is the useful figure when an axial-flux motor must keep pulling, climbing, hauling or generating without overheating. Axial-flux designs can package substantial torque into a short motor, but their real sustained output depends on how effectively the stator sheds heat and on the speed, voltage, ambient temperature and cooling conditions behind the rating.
What continuous torque tells you
Continuous torque is the torque a motor can maintain within its specified thermal and electrical limits at stated operating conditions. It is not a single universal property of a motor: speed, supply voltage, ambient temperature, coolant temperature and flow all affect the operating point. A rating without those conditions is difficult to compare with another motor’s.
Peak torque answers a different question: how much torque the motor can produce for a limited interval, often during acceleration. A 20-second peak rating may matter for a launch or brief pass, but it does not establish what the motor can deliver through a long climb, sustained towing, or continuous power generation. For those jobs, compare continuous torque at the relevant speed and conditions.
Why axial-flux motors can be difficult to cool
Axial-flux geometry places magnetic flux parallel to the motor shaft. This arrangement can produce high torque and power density in a short axial package. But in common dual-rotor designs, the stator sits between the rotors, restricting access to its surfaces and complicating heat removal.
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- High‑Quality Material: Multi‑layer PCB coil structure, high‑strength transparent acrylic stacking bracket, durable propeller and metal fasteners. Precision‑assembled magnetic components for stable power output.
- Practical Design: Unique stacked axial‑flux structure, visible internal coil layout. Equipped with propeller for intuitive high‑speed rotation demonstration, adjustment knob for convenient speed control.
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A 2026 SAE International paper identifies three related engineering challenges: losses associated with concentrated-winding harmonics, thermal management of the stator and rotors when the stator is sandwiched between rotors, and the manufacturing difficulty of segmented stators. These are not reasons to dismiss the topology; they explain why a compact motor’s sustained output depends heavily on its thermal and manufacturing design.
How cooling raises sustained torque
Motor current produces torque, but it also heats the windings. If heat cannot leave quickly enough, the motor must limit current to stay within its temperature limits. A more effective thermal path can therefore permit higher winding current density and a higher sustainable torque operating point. The result depends on the design; a cooling method is not a universal torque multiplier.
Rank #2
- Delivers up to 10.4 kg thrust per axis
- Engineered for 2.5–5 kg single-axis payloads
- Optimized for use with 18–24 inch carbon fiber propellers
- Supports a broad voltage range from 6S to 12S
- Lightweight motor design at 214g
In-core coolant channels
An IEEE study of a YASA axial-flux motor described channels that carry coolant through the stator core, with a continuous path through the stator segments. In its 36-kW case, the study reported an allowable winding current density of 15.5 Arms/mm2 and a 60% increase in torque capability compared with conventional stator-jacket cooling. Those figures belong to that study’s design and comparison, not to axial-flux motors generally.
Direct air-gap oil cooling
A 2026 SAE International study of direct air-gap oil cooling reported 96.5% peak efficiency, a 15°C reduction in stator-core temperature, and 0.3 N·m of drag torque above 500 rpm. The drag figure matters because cooling methods can bring their own losses; a lower temperature alone does not establish that a system is better across every speed or duty cycle.
Rank #3
- 【Wide Application Scenarios】: Ideal for axial flux generators, DIY wind turbines, and micro hydro power systems. Suitable for small-scale off-grid energy projects, DIY renewable power builds, and backup power setups, meeting various low-power generation needs.
- 【Coreless Disc Coil Design】: Features advanced coreless technology to reduce iron loss, enhance power generation efficiency, and minimize magnetic drag. The disc-shaped design ensures smooth operation and stable performance in DIY power systems.
- 【Precise Dimension Options】: Available in 4 specifications: 90mm diameter × 5mm thick, 90mm × 9mm thick, 160mm × 5mm thick, and 160mm × 9mm thick. Each variant is made to exact dimensions for proper fit in different generator builds.
- 【Durable Construction】: Built with heat-resistant materials rated up to 105℃ for reliable use in diverse environments. The robust winding structure resists wear and maintains consistent output during long-term operation.
- 【Efficient Power Generation】: Designed for 300W power output, delivering stable energy conversion for small-scale power systems. Ideal for DIY enthusiasts building low-wattage renewable energy projects at home or off-grid locations.
Cooling and winding design together
Cooling is only one part of the design. Winding layout, magnetic circuit, operating speed, inverter limits and the thermal route from the windings to the coolant all affect the result. A published improvement for one motor should not be applied as a prediction for another without matching its design and test conditions.
What published comparisons show—and do not show
Published studies provide useful examples of what a particular design achieved, but they do not establish a single best axial-flux motor or a market-wide efficiency advantage. The figures below come from different studies and product specifications, so they are not a like-for-like ranking.
Rank #4
- 1.Advanced 12N14P Brushless Motor – 12 stator slots and 14 permanent magnets provide low cogging, smooth start‑up, and stable rotation.
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- 3.Energy Efficient – Typical operating power only 4‑5W, ideal for battery‑powered or low‑power systems.
- 4.Speed Adjustable – Built‑in potentiometer allows continuous speed control from 1000 to 1500 RPM.
- 5.Quiet & Balanced – The 85 mm 3‑blade propeller and precision motor reduce vibration and noise during high‑speed rotation.
| Example | Reported result | How to interpret it |
|---|---|---|
| IEEE YASA cooling study, published in 2024 and appearing in a 2025 journal issue | In a 36-kW case, 15.5 Arms/mm2 allowable winding current density and 60% more torque capability than conventional stator-jacket cooling | A study-specific comparison of cooling approaches, not a universal gain. |
| IEEE Halbach-array axial-flux PMSM study, published in 2024 and appearing in a 2025 journal issue | For a 5-kW prototype: 30% higher torque density than its radial-flux comparison, 40°C lower coil temperature than its surface-mounted design, 25% lower losses, and 5–10% better efficiency across the speed range | The 30% figure is relative to that study’s radial-flux reference. The results do not establish the same advantage against every motor or duty cycle. |
| Turntide AF400S, current manufacturer product page | 290 N·m continuous torque, 106 kW continuous power, and 96% peak efficiency at continuous load | The stated ratings are at 45°C ambient, 55°C coolant inlet and 8 l/min coolant flow; Turntide says derating may be required above those conditions. |
| Turntide AF430S, current manufacturer product page | 443.8 N·m continuous torque and 101 kW continuous power | The cited figures do not establish matching test conditions or a directly comparable torque-density result. |
| Turntide AF125–AF440 range, 2026 Periodica Polytechnica Transportation Engineering review | 59–376 kW continuous power and 100–1,040 N·m continuous torque | A range-wide summary; it is not a single motor rating or a controlled comparison with another manufacturer. |
| EMRAX motors, 2026 Periodica Polytechnica Transportation Engineering review | 92–98% efficiency; optional air, liquid or combined cooling; EMRAX348 reported at 500 N·m continuous torque | The review does not provide one common test condition for the efficiency range or a directly comparable torque-density figure. |
| Sumitomo Electric axial-flux operating points, 2025 | Published efficiencies from 93.2% to 94.8% | Operating-point figures illustrate why efficiency should be checked across a duty cycle rather than inferred from one peak value. |
The Halbach-array study reported a percentage advantage in torque density but the cited result does not give a comparable mass- or volume-normalized value in N·m/kg or N·m/L. Without matched definitions, operating points and test conditions, the published figures cannot identify a universal torque-density winner.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to compare axial-flux motors for a vehicle or machine
- Match continuous torque to the operating point. Record the torque and speed needed, then check the motor’s continuous rating at that speed. Capture voltage, ambient temperature, coolant inlet temperature and coolant flow with the rating. For the Turntide AF400S, the manufacturer specifies 45°C ambient, 55°C coolant inlet and 8 l/min flow, and warns that higher conditions may require derating.
- Compare torque density on the same basis. Ask for continuous N·m/kg and N·m/L at the same speed and thermal conditions. Check what is included in the mass or volume—motor alone or the installed system—and whether the figure is continuous or peak. A peak torque-density number can favor a short burst rather than sustained work.
- Trace the thermal path. Identify whether heat leaves through stator jackets, in-core channels, fins, direct air-gap oil cooling or another arrangement. Ask for the conditions used to establish the rating, including coolant flow and inlet temperature where relevant. The cited IEEE and SAE studies show that thermal design can materially affect allowable current, temperature and losses.
- Use an efficiency map for the duty cycle. A single peak-efficiency number does not describe stop-start driving, towing or sustained high-speed operation. Compare a torque-speed efficiency map over the operating points the vehicle or machine will actually use. Sumitomo Electric’s published operating points, for example, range from 93.2% to 94.8%.
- Separate short-duration peak from sustained output. Get the peak torque value, duration and recovery or thermal limits as well as the continuous rating. A brief peak may help with acceleration, but it should not be used as the basis for a sustained towing or climbing requirement.
- Check the integration constraints. Confirm inverter voltage compatibility, shaft interface, cooling connections, NVH requirements, service access and ingress-protection rating. For a product such as Turntide’s, its published information includes ISO 4156 spline, voltage, IP and environmental-rating details; verify the exact variant against the vehicle or machine design.
Is there a single best axial-flux motor for torque density?
Not on the evidence cited here. The studies use different prototypes, comparison motors and test conditions, while manufacturer product figures do not by themselves provide a standardized, like-for-like torque-density comparison. The reported 30% advantage in the IEEE Halbach study applies to its 5-kW prototype and radial-flux reference; Turntide and EMRAX figures describe different product ranges and do not establish a common ranking.
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For a real selection, define the required continuous torque-speed operating points first, then compare complete motor ratings and package measurements under matched thermal conditions. If a supplier provides only peak torque or omits the conditions behind continuous torque, request the continuous torque-speed curve and the assumptions used to rate it before treating the number as comparable.
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