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Oxford YASA Motors Shows Specific Torque Above 30N·m/kg

A picture of the YASA topology. Source: Woolmer and McCulloch 2007. Click to enlarge.

Recent results from certified dynamometer testing has demonstrated that the 23 kg Oxford YASA motor produces a peak torque of 700 N·m (516 lb-ft), pushing its specific torque to more than 30N·m/kg. The company has also received the second tranche of £1.45-million (US$2.3 million) investment funding.

The Yokeless And Segmented Armature (YASA) topology is a new type of axial flux motor that has no stator yoke, a high fill factor and short end windings which all increase torque density and efficiency of the machine. The topology is based around a series of magnetically separated segments that form the stator of the machine. The novel design is enabled by using powdered iron materials that enable complex magnetic parts to be manufactured easily.

The YASA motor shows a step change improvement in torque density—initially with 20N·m/kg, or typically at least 2 times better than the best alternatives, according to the company. The improvement in specific torque comes from the combination of patented improvements in the magnetics, the cooling and the packaging of the motor.

We already have our sights set on the next generation YASA motor, which will push specific torque towards 40N·m/kg. This will enable the company to deliver a range of exciting direct-drive products with unparalleled performance.

—Nick Farrant, CEO of Oxford YASA Motors

Direct-drive electric motors are increasingly viewed in motor racing as the most efficient method of delivering quick acceleration as well as capturing a high percentage of energy from braking, th company said. Over the next 12 months, Oxford YASA Motors will be installing systems into new racing vehicles and TTXGP motorcycles.

The company is continuing to develop new markets for hybrid and electric vehicles, through ongoing collaborations with Delta Motorsport and Morgan Motor Cars in the UK, plus Electroengine in Sweden.

Oxford YASA Motors was founded in September 2009 to commercialize the YASA electric motor, developed by Dr. Malcolm McCulloch and Dr. Tim Woolmer at OXford University. McCulloch, head of the Department’s Electronic Power Group and Woolmer, then a PhD student in the group, originally devised the electric motor for the 2008 Morgan Lifecar.




A 12-inch tread radius on one of these in-wheel motors would give a static thrust of over 500 pounds. One on a motorcycle could give a thrust/weight of 0.5, and 4 on a car like a Mini Cooper could get close to 1:1.


That is very impressive. But we need to know the power or at least how many RPM it can do so we can derive the kW.

I'm betting that it's going to be over a 23kg package!


Over 275 KW in a 23 Kg package, that's much better power torque/density than recent ICE units can do. Coupled with ESStor ESSU, it could make a more than decent e-vehicle.


When will we see this 23kg in a suburban passenger locomotive or would it be too much grunt.?
The bigger unit will need bigger test bed.

The pure research outcomes from GB are definitely par excellence.
The US has a similar demonstrated intellectual ability
but have institutional bottlenecks including severe community justice, ethnic prejudice and national interest that has to constantly battle with big buisness interests and the military.
Well the military is the biggest business but many citizens live an illusion and aren't aware of the links.

Tim Duncan

Does sound impressive. I wonder how it compares to Unique Mobility designs. They were the highest & fattest efficiency in acceleration and braking modes some years back when I worked on solar race car. The weight of the motor will add packaging options but is not the whole enchilada. See system (includes motor, controler, cooling system) efficiency peak and breadth. Also what is the mass of the balance of plant, controler and cooling? Hopefully these would be asgood or better as other high performace motors and this is truely a 2x kind of step.


With KERS back on the table for F1 next year, these have to be on every teams shopping lists.


The peak power is 100 kW and continuous is 50 kW.

The preferred installation appears to be inboard (one motor per wheel, driving a half-shaft) but if the size and weight scale linearly with power a half-size unit would make an excellent in-wheel motor. 11.5 kg isn't much more than a disc brake (maybe internal drum brakes can be added for parking and emergency use) and 4 x 25 kW motors should be able to drive almost any passenger vehicle. 4 x 50 kW acceleration power is plenty, and AWD with no impact on interior space is a huge plus.


I think having one driving the front axle with a small ICE mounted in the rear and driving the rear axle would be quite neat.


It would be interesting if there was the possibility of a Michelin style in wheel motor with integrated suspension. That would keep the packaging efficiency high and can provide ride (pitch)control for short wheelbase vehicles.


Another invention based on clever geometry.

What it does is apparently the reduction of weight by reducing the amount of iron used.
For the same power/torque of the machine, the mass will be lower, which is desirable for in-wheel installations or on half-shafts.
It's also advantageous for light-weight, racing and high performance sports cars.

But the price of assembled e-motor per unit of power/torque is not likely to drop significantly, as the iron is much cheaper component in e-motors than the rare-earth magnetic material used and copper wire.


When you look at the demonstration video, they show two running. They also show a small car that uses them. Since they have them directly connected, they are counting on the the torque for acceleration from a stop.


MG good points, but also less copper wire used in the windings.. that saves $$ and reduces IR losses. I think the application would be in-wheel motors which I heartily approve off. Probably some weight savings in the iron flux ring used to trap the magnetic fields.

Maybe they could even use aluminum wire if the efficiency hit is not too big... save a few ounces.

BTW, I really hate CV joints and their pain-in-the-neck rubber boots.


Thanks for the link Engineer-Poet. Yeah, now that I've had time to go through their website, it looks like this is on the same scale as the Remy motors in terms of power and torque per kg.

Yasa still has a great motor, but not the "2x more than any alternatives" they claim in the press release.

They aren't publishing their power curves yet, that I can find, but I bet they look fairly similar to those from Remy.

Guessing at their numbers, I bet their torque falls of pretty quickly at about 1,400RPM.
100kW / (700Nm * 2Pi)*60,000 = 1,364 RPM

I wonder what it's RPM limit is and how well it could work as an in wheel motor for top speed?? Without some type of gearing, it seems like it would be limited on the high end.


Proton/Detroit Electric had an axial design, Lynx has had one for a while. There are advantages, but the application makes the difference. I like axial motors, I think they may become popular over time.


Here is an image of the Detroit Electric axial motor.

You can see that it takes the place of the transfer case it is so thin.
This allows a lot of flexibility for installations.

That link shows the Lotus Elise and other models they are working on.


Do you know what happen with Michelin in-wheel motor? Volvo Recharge and Mitsubishi i-Mev were making vague attempts to implement in-whee and finaly stoped trying. They decided simply make EV without any added values. For a while I have not heard any gossips.


I favor the in board shaft to wheel design. You can use several different types of motors for different cars. Sure there are U joints and boots, but cars have used those for a long time.


And they've been a hassle for some time, too. ;-)

The in-wheel motor has the advantage of eliminating both the weight of shafts and the bulk of the system inboard of the ball joints. In-wheel motors can turn just about any wheel into a drive wheel, without modifying the suspension or redesigning bodies for transfer cases and differentials. It eliminates CV joints and their maintenance. It's the future.


We will see what is used. When you add the weight of wheel motors, you will probably need to beef up the suspension. Doubling the weight at each wheel changes the response characteristics. Wheel motors have limited power, so for many vehicles you have no choice but all four wheels, which is expensive.


The weight of the wheel motors isn't supported by the suspension. On the other hand, it does increase the moving mass so greater damping is required (or lightening the wheels and tires to compensate).

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