Belgian startup Magnax has found a way to mass-produce the axial-flux motor
spectrum.ieee.org
spectrum.ieee.org
Another positive impact to GA is you don't need to adjust for mass and balance that much, batteries have a fixed center of gravity that does not change while discharging, while fuel tanks impact the plane's center of gravity as they go from full to empty. Less trimming, simpler flying.
And not the last, it is eliminating any problems with carburetors, mixture, air density or inverted flight: none of these affect an electrical motor, but it needs to be considered for the likes of Cessna where you need to adjust the (fuel/air) mixture depending on the altitude.
And it improves propeller efficiency, simplifying constant speed propeller operation. It can be easily fully automated.
All good news, but seeing it happen is a different story: it can take 3 to 5 years, more that a decade or never to reach mass availability and adoption in general aviation. It has the potential to make the market explode (in the positive way), but there is so much politics involved there are chances the status quo will be maintained. Let's see.
Later edit: I did some calculations, the result is less than 30 minutes.
Also, you could use structural batteries, which would substitute for part of the plane structure.
I don't, however, get the point about propeller efficiency, as is it not about matching the pitch to the airspeed? Fixed-pitch propellers have a maximum efficiency at one particular airspeed (and maximum thrust at, in general, a different particular airspeed), regardless of what sort of motor is turning them.
If you play with the propeller pitch, the force on the engine will make it change the rpm; if you change the engine rpm to the optimal of your propeller, you don't always have the best pitch, so you adjust it and this will impact the rpm. With an electrical motor the power delivery is much more robust, so you can adjust the pitch and then set the motor to the desired rpm and that's it.
Normal operation of a constant-speed propeller involves setting the desired rpm via the pitch control, and then adjusting the power, via the throttle, according to your purpose (such as level cruise at a specific IAS, or climb at maximum sustainable power), with the propeller govenor maintaining the chosen rpm via pitch changes, and I do not see how electric power changes this relationship. I understand that electric power might simplify making a sort of FADEC for electric airplanes (so that there is only one power control), and that constant-speed propellers could eke out more duration from the batteries, but now you are adding the cost and complexity of a constant-speed prop. I am not sure that it would be justified in a light airplane having a cruise speed not much higher than its best climb speed.
There are many planes in Europe that have the cruise speed much higher than the best climb speed. The best climb speed is around 100-120 km/h for light planes, while several plane models have the cruise speed over 200 km/h, up to 250 km/h. I am not aware of any plane with cruise speed below 200 km/h to use constant speed propellers, they have fixed pitch propellers, but the faster ones have in-flight adjustable pitch. I personally flew 7-8 different models of planes, only one with adjustable pitch, but they were all in the LSA class and const-speed is not used there.
Am I absolutely wrong or is it not actually much of a factor?
On the other side, large planes carry a lot more fuel as a percentage of the total mass, it really matters to them.
It shouldn't be a large factor. Drag is independent of mass, and while lifting the fuel to cruising altitude takes energy, most of the flight should ideally be cruising.
The rocket equation doesn't apply; that's for an entirely different regime.
Also, bear in mind that it's much easier to accurately and reliably measure a battery's state of charge than it is to measure how many gallons of fuel are in an airplane's wing.
I hope they succeed.
Its an interesting time to be alive. I'm not THAT old and when I was a kid a generic NEMA 50 HP industrial electric motor took a crane or at least a large engine hoist to lift, more than 500 pounds for sure, but now there are high end automotive motors that I can easily do bicep curls with (like 40 pounds)
VFDs are kinda like that too. What used to be a large rack is now a little tiny DIN unit that handles 10x the power.
See: https://m.youtube.com/watch?feature=youtu.be&v=BTuCshX5bc0&t...
They would still need to include a light thrust bearing on the double rotor design since you can never assume perfectly balanced air gap and one side or the other will dominate, but the losses would be much lower with that setup.
Also, during operation, is not each magnet in the motor being simultaneously pulled by the pole it is moving towards, and pushed by the pole it is moving away from? If so then, at any given point in the rotation, the axial force would be the net of the two effects.
...
Conclusion... ...Based on the results presented herein, the RFPM machine still appears as a better choice for a direct-drive generator, than the AFPM machine with slots"
Anyone can subscribe to the paper version and it's $40 for 12 issues international (or $20 in US): https://ieee.omeda.com/ieee/r-paid.do?p=WEBPAID
They are obviously making huge strides for a hardware startup if they're already field testing, so writing style opinion differences aside, mucho respect and I hope they succeed as well.
But I do hope they do not proceed with the in wheel concept. In wheel motors make the ride not only bumpier but more dangerous. This is because the wheel with more un-sprung weight bounces more and tends to lose contact with the road more, which in turn makes the car more likely to spin out of control, miss a turn, etc.
Electric cars, being still relatively new, cannot afford to get a reputation for danger.
The idea with motors at the wheel seems to be that the moving parts are all concentrated there. No mechanical distribution. Compartmentalization. But that is not incompatible with active suspension systems.
An active suspension requires power, too. And a heavier wheel would presumably require a more power-hungry active suspension than a lighter wheel, so you're not getting something for nothing in terms of efficiency.
I guess it is a matter of numbers, though. A CV axle also gives a wheel inertia, as it has mass and moves when the wheel does (partially). If you can make an insanely light motor, maybe you could make it so light that it's actually contributes less inertia than a CV axle would, in which case go ahead.
The Lohner-Porsche was a hit at the World's Fair in 1900 and was in development before that. I mean I guess a concept 120 years old is still new enough to get a bad reputation...
If there was a design tradeoff that allowed to somehow massively sacrifice efficiency for very low low specific mass and extreme heat tolerance, we might see the discs replaced with in-wheel "harvesting brakes" in addition to inboard high efficiency cruise motors.
But #1 I doubt that kind of tradeoff exists, at least not in sufficient magnitude, and #2 it would probably be quite uneconomic to exploit, lots of lower hanging fruits to pick first.
Also, a larger rotor weighs more than a smaller one.
Combined, a large wheel and tire will require more energy to move and to stop, and will add as 75 pounds or more to the weight of the vehicle. This has negative impact on handling and fuel economy.
The only reason why the manufacturers add a large wheel option is because people want them.
Larger wheel vs larger rim is not the same thing. A larger wheel has a larger weight but smaller rolling resistance. A larger rim on the same sized wheel has better handling characteristics and more room for larger discs, whether it is on a performance vehicle or a regular one doesn't really matter, plenty of mid-sized sedans of today are yesterdays performance vehicles.
There are outside exceptions (any SUV, ridiculously sized wheels on many American cars and people driving trucks when a normal passenger vehicle would be more appropriate). Those do have worse handling and fuel economy, but they're the exception, not the rule.
[edit]
Disc brakes add about 9.5kg on the front[2] (maybe half that on the rear?), so a single disc brake rotor weighs more than the entire weight of all 4 motors.
Obviously this is using Magnax's numbers for very large motors and assuming they scale down, which is silly, but clearly there is some weight at which it would make sense, particularly for a non-high-performance vehicle (1 motor per wheel has lots of advantages for handling, but AFAICT this is not unique to in-wheel motors).
1: https://www.tirerack.com/wheels/tech/techpage.jsp?techid=108
In a light vehicle, it's very important to minimize unsprung weight for the reasons you've listed. Not so much with a heavy vehicle.
Trucks and trains are often not sprung, and can benefit from lighter, smaller,more efficient hub motors. Cooling is easier when the whole motor is moving through the air.
More than the body needs to weigh enough, you need a proper center of gravity via weight distribution or you're simply going to tilt the thing over and wreck everything when you lift an object (source: have multiple sit/stand/clamp lift certifications.)
"Size matters, in forklifts, which need to maneuver in tight spaces."
That's why we made the reach forklift, which is operated while standing up. Half the footprint of a traditional forklift with the ability to reach out across a shelf to pick up a pallet.
Where this will make even more sense is for driving conveyor belts on assembly lines. You'll save more power there in a manufacturing warehouse environment than you typically will switching your entire forklift fleet over to these new motors.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.678...
https://en.wikipedia.org/wiki/MagneRide
https://www.youtube.com/watch?v=hiaMpG4Y640
Further, on newer vehicles with the trend of 20inch+ rims, that is already 60-90+lbs (27-40+kg) of unsprung weight per wheel with tire. There is certainly room there for improvement to offset at least some of the motor weight.
Would have to know how much their in-wheel models would actually weigh though to determine beyond speculation if it could be reasonably compensated for in a highway vehicle.
Watching the video that was linked in another thread, it made me think that maybe the hub could be stationary, and the tire just spins around the outside. That could cut down a lot on wind resistance.
>Electric cars, being still relatively new, cannot afford to get a reputation for danger.
I'm really sick of this "anything that measurably effects handling in a negative way is a non-starter because safety" attitude that's become increasingly pervasive. The fact of the matter is that there is a range of handling that is "acceptable" and anything in it is fair game. Nobody is expecting a Dodge Journey or a Spark EV to handle like a Porsche. At 15kwh/kg these motors will be fine for vehicles with average power to weight ratios that do not place a massive emphasis on performance (i.e all the "appliance" vehicles that purists hate). For low power levels these motors may weigh on the same order as the parts you need to transmit power to the wheels in a conventional applications so there might not even be any net gain in some applications.
The engineering feat is impressive and exciting, but this conclusion doesn't account for the Jevons paradox. In itself, a technical progress that improves the efficiency with which a resource is used doesn't lower the demand for this resource, but instead increases it. The solution to a more livable planet is political, and this is why it's so difficult to find.
Perhaps if every person embraces the politician within themselves.
https://www.magnax.com/magnax-blog/axial-flux-vs-radial-flux...
It will be interesting to see how Moore's law will materialize in EVs. Understanding that the majority of time and effort spent in the automobile industry has been aimed towards combustion engine design as opposed to electric motors, it will be equally interesting to follow the efficiencies to be discovered in the imminent future, taking into consideration how blazing quick they already are today.
No gear box, differential or CV joints. Potentially really cheep.
One curiosity for me is whether putting the motor in the wheel will work well. It's important to keep sprung weight as low as possible for suspension reasons. Then again, many (most?) electrical vehicles will be run on smooth roads.
I do know of axial flux motors that couldn't have had iron teeth, but I think it was a single-side design with a metal backplate to support the resin-soaked stator windings. I recall a nice discussion about them using GaN power electronics to reach very high efficiencies. Those machines were still hand made last year, however...
1) I don't consider this a breakthrough. 2) Magnax's motors are a really sensible design (like Emrax's) and I think they'll do very well.
Radial flux motors can achieve just as high of specific power and are already pretty cheap and available. I think it has taken a while for BLDC motors to become cheaply available at high specific powers except for R/C applications, and there wasn't really any fundamental reason why, but it's better late than never.
(I make high performance electric motors, including both radial and axial flux ones)
The batteries are the big pain point. A battery that's 50% lighter, has 50% more capacity and costs the same would trigger a technological revolution.
I find this surprising. Perhaps a big chunk of this is air conditioning, which is technically using a motor to run a compressor?
Interesting thing to consider is that reverse cycle airconditioners are notoriously inefficient compared to dedicated cooling or heating units..
Reverse cycle units can use anything from 2 times to 5 times the power of a dedicated unit on cooling
Do you have a source or a concrete example for that?
The most plausible explanation I can think of for what you're saying is that you're comparing an evaporative cooling system to a heat pump based one, in which case the 'reverse cycle' aspect is not the thing causing the inefficiency.
Example conversion motors: https://www.evwest.com/catalog/index.php?cPath=8
A general rule-of-thumb is that it takes about 100 watt-hours to move a thousand pounds of car one mile. I just started on a project to convert a Mazda RX-8 to electric. That's a 3,000 pound car (before the conversion), and I'm planning to use a Netgain Hyper9 AC motor, which is 120 pounds, which is pretty small compared to the rest of the car (or compared to the original rotary engine). Battery weight is the bigger concern; if I can keep the pack under 400 pounds I'm doing pretty good, and I'll be lucky if that gets me 100 miles of range.
One concern: I saw some designs with the rotor outside the stator, physically mounted to a wheel. I'm not a mechanical engineer, but as a guy who considers himself not quite dumb enough to fail at everything...
I hope they build those motors tough. Typical electric motor mounts create a situation where the only real stresses on the motor are rotational, along the axis of rotation, or in the case of a pulley / gear-mount setup, you are usually limited to 1-2 additional push/pull axis. But on a wheel? That wheel is going to want to rotate and move on all axis, which now needs to be supported by a motor, which also includes permanent electric magnets.
Awesome lighter motor, awesome that we can sandwich the rotor between stators (more layers more torque!).
One of the first questions that popped into my mind was how would this motor with less mass (less structure) handle 5 times the power/mass of traditional electric motors which are already pretty power full and sometimes break from strain.
>We believe that we can scale the design to whatever size carmakers (and other customers) may demand.
Count the weasel words. I'm at 5.
Wouldn't one expect a prototype to be better than a mass produced unit? It gets individual care and can be optimized for the test.
I judge by COTS pricing, but the $/kW falling on magnets increases a lot below 5~15kW electrical.
Seriously, though, this article is clear and well-written. I love it when I see people solve problems we didn't know we had. I'd figured we'd basically found the global optimum on electrical motors decades ago and were basically stuck there by physics now, with advances happening elsewhere in the powertrain. This development is like CPU vendors figuring out how to write 3x more single-core performance out of the same thermal budget after our own decade of stagnation in this area.