To put that kind of power production in perspective, the ludicrously fast 193-horsepower BMW S1000RR superbike of 2011 – a power-to-weight beast that would slay just about anything in the automotive world – has a lightweight motor that makes a puny 2.4 kilowatts per kilogram. So 9 kW/kg is no joke.

Which makes this axial flux, direct drive motor from Belgian company Magnax a real eyebrow-raiser. Magnax claims it makes a peak power no less than 15 kW/kg, with the ability to produce sustained power at around 7.5 kW/kg. To bring that back to the motorcycle example, if you built a Magnax motor that weighed as much as the BMW superbike's engine, you'd have yourself a 603-horse powertrain that could produce bursts of up to 1206 horsepower for short periods before overheating and needing to take it easy for a bit.

Obviously, that's a silly example, but these kinds of ultra-lightweight motors could do significant work towards offsetting the large weight figures of today's heavy lithium battery packs in electric vehicles. And until automotive-grade battery density takes a significant leap forward as it's been promising to for several years now, weight will continue to be a serious issue for e-mobility.

Benefits and drawbacks of Axial Flux Designs

While the vast majority of electric motors currently in circulation are radial flux designs, Magnax claims the key to the high power density it's achieving is the direct drive axial flux design used in all its motors, which uses a stator disc sandwiched between two rotor discs with small air gaps in between. Yokeless axial flux motors, the company claims, have a number of advantages if implemented properly. The flux path is shorter, and the magnets further away from the axis, leading to greater efficiency and leverage around the central axis.

What's more, the axial flux design allows Magnax to waste very little copper on overhanging loops on the windings. Magnax's motors have zero overhang; 100 percent of the windings are active, where the company claims radial flux motors can sometimes have up to 50 percent of their copper inactive, adding extra resistance and causing heat build-up. Magnax uses a rectangular-section copper wire in its windings to give the highest possible density. And the motors are much thinner than radial flux machines, meaning that you can stack them easily to work in parallel.

There are, of course, difficulties when it comes to building axial flux motors – otherwise everyone would be making them. Powerful magnetic forces acting between the rotor and stator discs tend to make it very difficult to keep the air gap between them uniform. If they start to wobble or bend, the discs can start rubbing against one another, leading to bearing damage at best, and rapid, spectacular unscheduled disassembly at worst.