Automotive

Magnax prepares to manufacture radically high-powered, compact axial flux electric motor

Magnax prepares to manufacture...
The Magnax yokeless axial-flux electric motor offers incredible power densities in what the manufacturer describes as a reliable, manufacturable and low-maintenance package
The Magnax yokeless axial-flux electric motor offers incredible power densities in what the manufacturer describes as a reliable, manufacturable and low-maintenance package
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Electric aviation is one target market for the Magnax motor
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Electric aviation is one target market for the Magnax motor
Because of these motors' extreme light weight, high power and thin profile, they're ideal for direct drive hub motor applications
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Because of these motors' extreme light weight, high power and thin profile, they're ideal for direct drive hub motor applications
Magnax motors can be mated to a transmission if necessary
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Magnax motors can be mated to a transmission if necessary
Lightweight and compact, the Magnax motor should be terrific in electric motorcycles where weight is paramount
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Lightweight and compact, the Magnax motor should be terrific in electric motorcycles where weight is paramount
An example of an electric car design using a Magnax motor through a gearbox
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An example of an electric car design using a Magnax motor through a gearbox
The Magnax axial flux motor is scalable through all kinds of sizes
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The Magnax axial flux motor is scalable through all kinds of sizes
Part of the lightweighting and power density advantage of axial flux motors comes from the large amount of useless overhanging copper on a radial flux design (left)
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Part of the lightweighting and power density advantage of axial flux motors comes from the large amount of useless overhanging copper on a radial flux design (left)
Radial (left) vs axial flux designs
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Radial (left) vs axial flux designs
Large diameter, high torque, low RPM versions can be manufactured up to 5.4 meters in diameter and beyond
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Large diameter, high torque, low RPM versions can be manufactured up to 5.4 meters in diameter and beyond
Large industrial-sized prototype on the test bench
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Large industrial-sized prototype on the test bench
Size advantage: on the left, a standard 300-kilowatt radial flux direct drive generator. On the right, three stacked 100-kilowatt Magnax motors offering superior efficiency
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Size advantage: on the left, a standard 300-kilowatt radial flux direct drive generator. On the right, three stacked 100-kilowatt Magnax motors offering superior efficiency
Stackable design gives design flexibility
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Stackable design gives design flexibility
The Magnax yokeless axial-flux electric motor offers incredible power densities in what the manufacturer describes as a reliable, manufacturable and low-maintenance package
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The Magnax yokeless axial-flux electric motor offers incredible power densities in what the manufacturer describes as a reliable, manufacturable and low-maintenance package

After nearly a decade in development, Belgian startup Magnax claims it has developed an ultra-high power, lightweight, compact axial flux electric motor with performance figures that blow away everything in the conventional radial flux world. Crucially, it says it's worked out how to manufacture them too.

It might not have the romance of combustion engine tuning, but it seems a bit of a battle is brewing to develop the kinds of high-performance motors that will power the electric cars, motorcycles, aircraft and industrial equipment of the future.

A week ago we wrote about Equipmake's spoke motor design, which allows it to pump out some 9 kilowatts per kilogram with exceptional cooling and continuous power production ability.

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.

The Magnax axial flux motor is scalable through all kinds of sizes
The Magnax axial flux motor is scalable through all kinds of sizes

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.

Radial (left) vs axial flux designs
Radial (left) vs axial flux designs

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.

Size advantage: on the left, a standard 300-kilowatt radial flux direct drive generator. On the right, three stacked 100-kilowatt Magnax motors offering superior efficiency
Size advantage: on the left, a standard 300-kilowatt radial flux direct drive generator. On the right, three stacked 100-kilowatt Magnax motors offering superior efficiency

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.

Magnax claims it addresses this in its yokeless axial flux design by having two rotor discs that constantly put equal and opposing forces onto the stator disc. The rotors are connected directly to one another via a shaft ring, so the magnetic forces cancel each other out, and the internal bearing doesn't have to deal with them.

Cooling is key with any high powered electric motor that's expected to do consistent work, and axial flux designs tend to suffer in this regard, since their stator windings are sandwiched between the rotor discs, making it hard to get heat out. Magnax claims its motor designs cool well, as the windings are in direct contact with the outer aluminum casing, allowing decent heat transfer.

Lightweight and compact, the Magnax motor should be terrific in electric motorcycles where weight is paramount
Lightweight and compact, the Magnax motor should be terrific in electric motorcycles where weight is paramount

It seems to be working. Continuous power figures for the Magnax motor come out at 50 percent of what it can make at its peak, which is pretty decent but not in the realm of the best-cooled radial flux motors. The Equipmake motor, for example, can continuously make nearly 70 percent of its peak power, suggesting superior cooling.

One further challenge comes with manufacturing, as the stator discs can be particularly hard to get right, and even harder to build in an automated high volume process. So when they do get built, they're hand-made and highly expensive as a result. Magnax claims to have cracked this problem too, with a number of "proprietary solutions" that allow it to scale and build these things cost-effectively.

Because of these motors' extreme light weight, high power and thin profile, they're ideal for direct drive hub motor applications
Because of these motors' extreme light weight, high power and thin profile, they're ideal for direct drive hub motor applications

Applications

The Magnax motor is highly scalable, ranging in size from 15 centimetres (~6 inches) right up to discs 5.4 metres (~13 feet) in diameter and beyond. They can be slotted in next to one another to run in parallel, and they can run either as direct drive or through a gearbox if you're willing to accept the efficiency losses involved.

Magnax is pitching them at electric cars and motorcycles, aircraft rotors, and as large-diameter, high torque, low RPM solutions for wind power, hydroelectric and wave power generation.

Large diameter, high torque, low RPM versions can be manufactured up to 5.4 meters in diameter and beyond
Large diameter, high torque, low RPM versions can be manufactured up to 5.4 meters in diameter and beyond

At the end of the day, field testing in the automotive and industrial worlds will be the proof of this pudding, but if this is truly a high-power, long-life, well-cooled, high-efficiency, low-maintenance axial flux motor, Magnax could be poised to make some serious waves.

The company has spent some nine years getting its tech together after a proof of concept was originally built at the University of Ghent in 2009. Now, it claims to have working prototypes and a manufacturing methodology sorted out. With a bit of luck, the rubber will hit the road soon and we can see if this truly is the electric motor of the future.

Check out a couple of videos below:

Magnax Axial Flux Motor - high speed prototype

Magnax Axial Flux Permanent Magnet Electric Motor / Generator

Source: Magnax

20 comments
notarichman
maybe electric generators driven by this motor will be feasible -- i'm thinking train/ship engines.
McDesign
Cooler motors every week, it seems!
ljaques
I'll bet that Zero is chomping at the bit to get these to put in their motorcycles. I hope it works out that these truly do work and go into production soon. It would make replacing the gas engine in my Toyota Tundra a viable possibility and make electric motorcycles even lighter, which is always a Good Thing(tm). Go, Magnax!
Darus Zehrbach
The second issue besides cooling with this design type is that since the force of the magnets is translated into torque in lb ft on Nm by the distance from the shaft center, with the magnets in the axial system, it is the average distance of all of the magnets acting that creates the torque. So on a motor of a given diameter, all else being equal, the torque is 1/2 that of a radial motor. So then you need to run higher amps, or do something else that is less efficient or more bulky. But there is a lot of software around to help you design an axial motor, but nothing for radial. So its not so much that axial is better, its just better for start up companies to get something working.
Paul Anthony
I would like to see an American company make a hub motor for bicycles using this technology.
korolexa
YASA e-motors also has more than 10 kW/kg https://www.youtube.com/watch?v=8XHdjpA4rWY avidtp also claims >10 https://www.youtube.com/watch?v=cDLUBL7ib-0 and here Bosh demonstrate its Induction motor which doesn't require gear box, extra cables... https://www.youtube.com/watch?v=HELSkIlT9Sc This just interesting Electric-Hydraulic Engine https://www.youtube.com/watch?v=qgN8U3Q_RcQ
Kpar
If this article (and video) are to be believed, we will hear a great deal about this in the near future.
Grunchy
The best permanent magnet motor I'd seen was the DRS PA44, producing 336 kW with a weight of 195 kg (1.7 kW/kg). This is approaching or even exceeding the power density of hydraulics. I heard this was technology demilitarized in the 90s, originally designed for American tanks. http://leonardodrs.com/media/3118/pa44-450-pm-motor.pdf (I would imagine the DRS motors might be a bit more rugged than the newer Magnaz motors).
guzmanchinky
"rapid, spectacular unscheduled disassembly" Best line ever.
Fast Eddie
This is very compelling. Whether the Magnex design makes it or not, it certainly shows that the Innovation Light is fully illuminated for electric transport!