British start-up YASA, acquired by Mercedes, has built the most powerful and lightweight electric motor in the world — and there’s still room for further development.
Mercedes acquired the YASA start-up on July 21, 2021, with the goal of using its new axial flux electric motors in future high-performance AMG electric models. The acquisition of the British company has proven to be a brilliant move, as YASA’s axial flux electric motors are becoming increasingly more advanced.
Recently, YASA developed an ultra-high-performance prototype that sets a new world record in power density, according to the company’s founder and CTO, Tim Woolmer.
This motor, weighing only 13.1 kg, delivers an incredible power output of 550 kW (758 PS), resulting in a power-to-weight ratio of 57.1 PS/kg (42 kW/kg).
With this achievement, YASA has surpassed the industry’s best performances. Previously, a Helix motor produced 650 kW with a mass of 28 kg (23.2 kW/kg), and another motor, the HPM 400 from Equipmake, delivered 400 kW with a mass of 30 kg (13.3 kW/kg).
YASA motors are permanent magnet synchronous motors (PMSM) with axial flux and a disc-like shape.
Unlike conventional radial flux PMSMs used in today’s electric vehicles — where the stator is positioned on the outside like a ring and the rotor coaxially inside — in axial flux motors, the rotor and stator consist of several rings arranged side by side along an axis. The magnetic flux moves parallel to the axis of rotation — hence the name “axial flux motor.” In conventional synchronous motors, the magnetic flux moves radially around the axis of rotation.
As a result, axial flux motors are more compact and lighter than conventional PMSMs and offer higher power density. But the major advantage is that they can be cooled more easily, since the components that heat up the most (the copper wire coils carrying current) are located on the outside.
However, due to the alternating ring structure, these motors are much more complex to manufacture — and thus more expensive.
That’s why YASA motors are used in expensive, sporty electric cars, such as the Mercedes-AMG GT XX concept, which previews the future Mercedes-AMG GT 4-door. It produces a total of 1,000 kW (1,360 PS) from three YASA motors.
Woolmer states that YASA motors do not use rare materials and are scalable for mass production between 10,000–50,000 units at reasonable costs for the premium segment. This motor will be tested this summer, and Woolmer hopes the world record will become official.