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► Why they’re the ‘Cosworth of EV tech‘
If you worry that Britain no longer produces brilliant engineers of the Frank Whittle variety, meet Dr Tim Woolmer, and YASA. Lamborghini has just announced that the new Temerario will use YASA’s brilliant, tiny, lightweight electric motors in its hybrid drivetrain, but the impact of what Woolmer is creating might go far beyond high-priced hypercars.
For more than 200 years we’ve known that there are two basic types (or ‘topologies’) of electric motor. There’s the ubiquitous radial-flux design, which is cheap and easy to produce and which powers everything from your Tamiya to your Tesla. It looks a bit like a sausage roll: the magnetic flux flows radially around the stator (the pastry) acting on the permanent magnets in the rotor (the sausage), causing it to turn. You know what a conventional electric motor looks like, and if you can’t quite picture how the electrons flow, there are plenty of animations online.
In 1821, Michael Faraday demonstrated the first example of the other kind of electric motor: the axial-flux or ‘pancake’ design. Here the stator and rotor are both discs, sitting next to each other with the shaft passing through the middle. The current flows through the stator axially, or in line with the shaft, acting on the permanent magnets in the disc-shaped rotor alongside it, causing it to turn.
The advantages of this design are legion. Because there’s more surface area for magnetic interaction and most of it is generated with greater leverage at the edges of the discs, an axial-flux motor can produce much higher torque for a given weight. Because the hot bits aren’t buried in the pastry, it can be cooled more easily and can operate at a higher percentage of its peak output for longer. And that pancake shape has obvious packaging advantages in any application but especially cars, where it can be slipped between a combustion engine and the gearbox in a hybrid, or even into the wheels of a pure EV.
The trouble was that nobody could work out how to mass-produce an axial-flux motor, until Woolmer came along. He saw that they would be perfect for electric cars, devoted his Oxford PhD to making them work at scale, and within five weeks had cracked the problems that had stumped everyone else for two centuries.
His solutions include (but aren’t limited to) getting rid of the heavy iron ‘yoke’ which previously held the stator’s copper coils, further reducing weight and bulk and allowing a rotor to be placed on either side; an oil-cooling system for the copper coils through which the current flows; and the rather beautiful, jewellery-like design of those coils, which are edge-wound from flat copper wire around cores of soft magnetic composite and sit in the stator like the segments of an orange. The firm he founded to put his ideas into production – YASA – sounds exotic, but stands for ‘yokeless and segmented armature’: essentially just a description of what he invented.
This was back in 2005, and in those pre-Tesla times there was little demand for EV motors. But as the market has grown exponentially, and Woolmer’s designs have grown in power, shrunk in size and taken shelter behind what he describes as ‘a thicket of patents’. Look at the YASA and Tesla motors on Tim’s desk and axial’s advantages are immediately obvious: YASA’s current design is around a quarter the depth of the Tesla motor, half the weight and makes twice the torque. It’s also a far neater, better-resolved design than the Tesla: a classic example of something looking right because it is right.
It’s still expensive though. YASA first supplied prototype, racing or very low volume road cars such as the Jaguar C-X75, Koenigsegg Regera and the Lola-Drayson electric land speed record car. In 2019 the Ferrari SF90 became first standard-production car to get a YASA motor, followed by the 296 GTB. The Lamborghini Revuelto hybrid uses two on the front axle to assist its V12, and the Temerario adds a third on the rear axle. Lambo’s forthcoming full EVs will be entirely YASA powered. McLaren is also reported to be a customer.
The biggest beneficiary of Woolmer’s tech is likely to be Mercedes, which bought the company outright (but excluding Evolito, his aerospace division) for an undisclosed sum in 2021. YASA now employs 500 people in the UK, and will continue to supply the supercar makers from a plant near Oxford which can now make 25,000 motors each year after a £12m investment. But Mercedes will start building them in the hundreds of thousands for its AMG.EA platform at a new plant in Berlin.
Axial-flux motors might give a new generation of all-electric AMGs the engineering distinctiveness which we all feared might be lost in performance cars in the EV age. Other than the packaging flexibility, the compounding effect of mass reduction means the 100kg saved by the motors themselves is at least matched by what can then be saved elsewhere in the car: in the battery especially.
But the greater benefit might come from what Woolmer does next. YASA is developing motors of around 225kW – or 300bhp – weighing just 7kgs. That’s less than a conventional brake disc. Put that motor in the wheel – as the Mercedes Vision One-Eleven concept did in 2023 – and there’s no increase in unsprung mass, so no effect on the ride or handling of the car. But the weight savings really start to multiply: no driveshafts, possibly no gearbox, and if the law is changed, no conventional friction brakes either; the electric motors doing as effective a job of shedding speed as creating it.
Radial-flux motors won’t be rendered obsolete, of course. Rimac and Lucid in particular are making huge strides in the power density of their motors, which are hardly disadvantaged by being shaped like sausage rolls: Aston Martin gave Lucid a stake in the company in return for access to its tech. Axial-flux motors are likely to remain relatively costly and lower-volume, and their most dramatic impact might not be in automotive at all. Aerospace companies will pay way more to cut weight than carmakers and the compounding effects of weight loss are greater. Evolito is developing extremely expensive, lightweight axial-flux motors which could produce a colossal 50kW per kg, and which might enable practical, affordable, short-hop electric flight. If that happens, the comparisons between Woolmer and Frank Whittle might be more than academic.