"Weight down, size down, cost down, efficiency up": how a British firm is revolutionising electric motors

Oxford-based Yasa was recently bought by Mercedes-Benz. Steve Cropley finds out all about its game-changing tech

- By Steve Cropley

All electric motors, you might well think, are endearingly simple, cylindrical, sausage-shaped and similar in weight and efficiency. They have few moving parts and are much smaller than the combustion engines that they are busy replacing in the world’s cars. Official figures say they make great use of energy, too, producing efficiency figures heading towards 90%. That sounds great, given that the latest and best petrol and diesel engines are well south of 40%.

The truth is less simple. Most current EVs do indeed use sausage-shaped radial-flux motor technology, but in the past few years, a radically different, British-developed, dog-in-the-manger design called Yasa has emerged – an axial-flux electric motor in a disc-shaped layout that’s more efficient and much lighter.

Yasa (standing for yokeless and segmented armature) motor design has already started bringing huge reductions in size and weight to EVs, although not yet mainstream ones. But that’s coming.

In essence, a Yasa motor ditches about 25kg of iron in a Tesla-size sausage motor, replacing it with a much more compact mechanism framework weighing around 3kg. And as a result of its continual development in the hands of an inspired Oxford PhD student, Tim Woolmer, a dozen years ago, its efficiency keeps improving to the tune of 25% per year.

Woolmer says the Yasa principle was “a known technology” when he unearthed it for his PhD thesis in 2008 and built a 27bhp, 88lb-ft prototype that weighed a then promising 20kg.