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Donut Lab's next-generation in-wheel motors

donutlab.com

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Re: Donut Lab's next-generation in-wheel motors

#31

Post by johnwalkr »

lelanthran wrote: post #17
notjulianjaynes wrote: post #9

Earlier quoted context omitted.

If the weights are listed on the are to be believed, this shouldn't be an issue. It says 40 kg for a 21" wheel. A quick Google is telling me that a regular old steel wheel from a truck of the same size is around 50 to 80 lbs (23-36 kg). 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 s…

> If the weights are listed on the are to be believed, this shouldn't be an issue. It says 40 kg for a 21" wheel. A quick Google is telling me that a regular old steel wheel from a truck of the same size is around 50 to 80 lbs (23-36 kg). 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/…

I think it still needs the wheel, and all the related parts in the middle like an upright/steering knuckle, which probably cancels out any mass of the motor that is acting as a structural part of a wheel. Other things like brakes would still be required. These should allow for regenerative braking normally the braking torque of a motor is nowhere near the acceleration torque, plus they don't mention braking function anywhere so it's safe to assume there's no special performance there. In all, I would assume for now that a 40kg motor would add approximately 40kg to the overall wheel mass, possibly even more. It would be interesting to see if there's a concept for an inboard version of these motors and compare to others.

Re: Donut Lab's next-generation in-wheel motors

#32

Post by usrusr »

Neywiny wrote: post #21
exabrial wrote: post #18

There's a concept called "unsprung mass", which basically destroys handling of all vehicles from race cars to trucks. Basically the greater the unsprung mass, the harder it is to damp the input into the suspension because of the inertia of the moving suspension components themselves. An ideal suspension has zero undamped mass, and all input to the suspension is a direct result of contact with the surface the vehicle…

There's also the inertia problem where it's harder to accelerate mass that's further away from you. The classic spinning ice skater demo. This feels physically disadvantageous. Hopefully I'm wrong though, the more competition in spaces the better.

But here that mass is the driving force: the further away from the center you put your magnets, the less force (the less magnet) you need for a given amount of Newtonmeters. When you move that mass away from the center, you need less mass, changing at the same factor as rotational inertia changes. So no improvement or drawback in terms of rotational inertia, but improvement in terms of total mass (and improvement in terms of unsprung mass when comparing to a wheel motor in the hub).

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.

Re: Donut Lab's next-generation in-wheel motors

#33

Post by ricardobeat »

vlachen wrote: post #6

I spent a number of years designing outer-runner direct drive permanent magnet motors for industrial equipment and I've got some questions. 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 o…

This is an offshoot of a motorcycle manufacturer. They have this product on the market already, so there must be something you missed?

https://arstechnica.com/cars/2024/07/sci-fi-looks-high-end-p...

Re: Donut Lab's next-generation in-wheel motors

#34

Post by ricardobeat »

notjulianjaynes wrote: post #9
lelanthran wrote: post #8

Maybe they thought of this, but I didn't see any mitigation for the unsprung mass problem that these motors bring.

If the weights are listed on the are to be believed, this shouldn't be an issue. It says 40 kg for a 21" wheel. A quick Google is telling me that a regular old steel wheel from a truck of the same size is around 50 to 80 lbs (23-36 kg). 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 s…

They mention in their CES interview that putting two of these in the rear axle + a lighter version in the front can give you a 2500hp+ car. That is the other breakthrough, and matches the comparison chart they have on the website against other tech.

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.

Re: Donut Lab's next-generation in-wheel motors

#35

Post by usrusr »

vlachen wrote: post #6

I spent a number of years designing outer-runner direct drive permanent magnet motors for industrial equipment and I've got some questions. 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 o…

The way I understand hubless wheel designs (powered or not) is that you don't build them as one big bearing, wasting huge amounts of load bearing capacity in all parts of the rotation that aren't the ground contact point. I assume that the moving part is the rim is designed as a rail, with tiny trucks (as in the rail car component) riding on it that are fixed to the non-moving part. You'd have a high density of strong trucks near the floor, some at the three and nine o'clock positions for braking and acceleration force and perhaps some flimsy guiding on top. Those trucks would not necessarily require more sealing (outside their own small bearings) than the rail/wheel contact in railroads need sealing. And moving that rail a little hubward, behind a lip that extends rimward would already get you strong centripetal forces driving out all ingress in contact with the moving part, and adding some overpressure (that you might need for cooling anyways) would help even more. I think it could all remain contactless on that first, whole-wheel level, at least if you don't design for routine wading.

Re: Donut Lab's next-generation in-wheel motors

#36

Post by xhkkffbf »

Is the control of these things good enough that there's no need for a steering mechanism? Or I should say "mechanical steering". Devices like the Segway steer by changing the wheel speeds just a bit. Could this deliver enough control to steer well enough at highway speeds? I'm guessing it could work in a parking lot.

Re: Donut Lab's next-generation in-wheel motors

#37

Post by Kelvin506 »

vlachen wrote: post #6

I spent a number of years designing outer-runner direct drive permanent magnet motors for industrial equipment and I've got some questions. 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 o…

Plus there's the unsprung mass. At least traditionally part of suspension performance is reducing the unsprung mass as much as possible because mass and spring rate inversely correlate.

Re: Donut Lab's next-generation in-wheel motors

#38

Post by vlachen »

esperent wrote: post #28
vlachen wrote: post #23

Earlier quoted context omitted.

It absolutely matters. Every Watt of energy that doesn't become torque at a rotational velocity is just heat. 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 l…

> Every Watt of energy that doesn't become torque at a rotational velocity is just heat. 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%?

Depends on the seal manufacturer. Those numbers are usually provided through their engineering data system. Their data will be fit to a particular tolerance for seal race surface finish, which will be influenced by the reality of manufacturing.

Re: Donut Lab's next-generation in-wheel motors

#39

Post by vlachen »

ricardobeat wrote: post #33
vlachen wrote: post #6

I spent a number of years designing outer-runner direct drive permanent magnet motors for industrial equipment and I've got some questions. 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 o…

This is an offshoot of a motorcycle manufacturer. They have this product on the market already, so there must be something you missed? https://arstechnica.com/cars/2024/07/sci-fi-looks-high-end-p...

I cannot speak to their actual means and methods. Maybe they've figured it out. But my experience designing and manufacturing similar products informs my skepticism.

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.

Re: Donut Lab's next-generation in-wheel motors

#40

Post by esperent »

vlachen wrote: post #38
esperent wrote: post #28

Earlier quoted context omitted.

> Every Watt of energy that doesn't become torque at a rotational velocity is just heat. 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%?

Depends on the seal manufacturer. Those numbers are usually provided through their engineering data system. Their data will be fit to a particular tolerance for seal race surface finish, which will be influenced by the reality of manufacturing.

Right, but are we talking closer to 5% or 50%?
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