Donut Lab's next-generation in-wheel motors(donutlab.com) |
Donut Lab's next-generation in-wheel motors(donutlab.com) |
Cheifly, bearings. They're not shown in any of the oh-wow images, but these will likely be the most expensive component of each motor. Big bearings are expensive, and to accept the loading of normal wheel operation, these will have to be pretty beefy. That's not even discussing operational life and maintenance.
After you've stuffed a pair of angular contact roller bearings into this "wheel", you're going to want to keep salt water and road grime from entering those bearings, so what do you use as a seal? Whatever you use is going to be big, expensive, and suck up huge amounts of power due to the large contact surface.
Finally, once you've got big ass bearings and big ass seals, how do you have enough room to put a decent amount of copper in there? Power in these things always amounts to maximizing the amount of copper in the space, and I just don't see room for it.
If so, is that heat another issue or is it a "don't care" because the heat is over a large enough surface?
Contact seals work by contact and friction, friction generates heat proportional to linear velocity and linear velocity goes up proportionally with radius.
The motors I designed were intended for food production washdown areas, and if I were designing large motors for use in road environments, I would use a lot of similar methods, including high quality contact seals.
Teflon seals would probably have the required capabilities, but they will get destroyed by dust and grit. Nitrile seals would do it too with the detraction of a huge power loss at the seal. I wouldn't trust a plain labyrinth seal to do the job.
https://arstechnica.com/cars/2024/07/sci-fi-looks-high-end-p...
I also look back in history and see many "revolutionary" technologies in the automotive/transportation space that didn't turn out as the inventors hoped. A veritable graveyard of "good on paper" ideas that failed due to the harsh realities of environment, maintenance, safety and manufacturing.
As I said in another comment, I want them to succeed. I am familiar with the great efficiency that a direct drive motor can offer. They can be great motors in the right application. But my evaluation of what I can glean through the marketing is that this particular product will end up in the graveyard.
I found [2] on YouTube, but it doesn't seem to contain any actual video of the vehicle (and the voice-over says "unit-rack" rather than "uni-track" which I didn't love).
That said, I was already thinking 630 kw per wheel was a pretty incredible claim before I realized these are apparently not much heavier than a non-mptorized wheel. These have to be some marketing department numbers or something. 630 kw is roughly 850 horsepower.
NB reminder that your employers legal policy may be to never look at patents.
There is zero chance this tech will make it into sports cars unless it can beat the weight of a magnesium or AL alloy rim. Even casual vehicles like minivans have rim weight minimized for comfort.
Not an expert :) just watched enough Donut media on youtubes :P
That's high enough that I have to assume it's for all four wheels... if it's for a single wheel, then an all wheel drive vehicle would have 2520Kw Power + 17,200 Nm Torque, which is 1.6x more than the most powerful production car in the world: the Lotus Evija (1,500 kW).
I don't see how you go from a single 286kW/510Nm hub motor x4 gets you 1500kW/9000Nm instead of 2520Kw/17200Nm. Wonder what the limitations are + what nonsense they are trying to pull in their single motor stats.
[1]: https://www.cnet.com/home/electric-vehicles/this-donut-shape...
Copper is heavy. So is silicon steel. So are high strength magnets.
I love the idea, but this one's going to have a real world bite in the ass once they get it out of the lab.
I'm skeptical; They say 40kg, but I think that's just for the motor, not the entire wheel. I working off the (maybe incorrect)[1] assumption that the 40kg doesn't include the steel/mag rim and the tyre.
As far as a 21" standard mag wheel, the tyre alone is around 12kg, so quite believable that a standard wheel with tyre would weigh maybe 30kg. However this still means that putting a tyre on a 40kg wheel is going to take it to +52kg.
[1] Just the minimum metal and rubber needed for a 21" wheel to maintain its shape and structure should be around 30kg. Maybe this motor is structurally round already, so doesn't need any rim to reinforce it?
Disk brakes add another 4-5kg, maybe their wheel hub doesn't need one? At these power levels, regen is probably stronger than the largest brake disc you could fit.
You'll also have at least 150kg less on the car (motor/differential). Hard to tell what handling would be like until someone builds a test car.
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The unsprung mass of a typical wheel/tire combination represents a trade-off between the pair's bump-absorbing/road-tracking ability and vibration isolation.“
In a way this is a transfer of semiconductor miniaturization to motors: when your power transistors can switch fast enough, you can replace fewer bigger coils with more smaller coils (that switch more often per rotation) and moving it all rimward gives you more torque per Newton. That ice skater effect? It's on your side.
At these weights, I suspect the vehicle won't handle as well as a vehicle with the motor offboard.
I still have my doubts, but I wish them luck. I've always wanted to get Kenada's bike.
Do you have any rough numbers to put on this? If there was 1000w of electrical power going to a wheel like this, what kind of heat loss are we talking? 5%, 10%, 30%?