Inside the YASA YM360: Axial Flux Motor Engineering Explained

TL;DR

The YASA YM360 achieves 360 Nm from just 15 kg by using both disc faces to maximize force-transmitting surface area while eliminating most steel.

Key Points

• 1.The YASA YM360 is dramatically lighter than comparable motors. At 15 kg producing 360 Nm and 125 kW (167 hp), it weighs less than a third of the BYD Tang traction motor (~40 kg) with similar output.
• 2.Larger diameter alone does not explain the torque advantage. A hub motor of similar diameter produces only one-third of the YM360's torque, disproving the common online claim that effective radius is the primary factor.
• 3.Magnetic shear stress is the true limiting factor for all electric motors. Steel saturates at ~2 Tesla and copper is limited to ~10–40 A/mm², capping usable shear stress at roughly 14 PSI (one atmosphere) regardless of geometry.
• 4.The axial flux design wins by using both faces of a disc. The combined surface area of the two rotor-facing sides equals that of the large radial flux motor, delivering the same torque with far less steel — roughly 30 kg less.
• 5.Soft magnetic composite (SMC) teeth enable complex, skewed geometry. Each stator tooth is made from insulator-coated powder metal compacted into shape, preventing eddy currents and allowing the skewed angle that produces smooth, sinusoidal torque with no ripple.
• 6.Oil cooling solves the axial flux thermal challenge. Oil (not water) circulates directly around each copper winding inside the stator, providing high-contact cooling while glass-fiber covers and thin magnetic end caps minimize air-gap losses.
• 7.A 1,000 hp version in the same package is already on Yasa's roadmap. Grain-oriented steel laminations — possible because axial flux keeps flux uni-directional — could replace SMC for even lower losses; Yasa is wholly owned by Mercedes-Benz and is currently in production for the Lamborghini hybrid.