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Comment by jama211 | Hacker News Reader

I don’t see anything inside the article that says it’s designed to be inside the wheel. I’m not sure where they got that from.

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From Wikipedia on Axial Flux Motors: >"Mercedes-Benz subsidiary YASA (Yokeless and Segmented Armature) makes AFMs that have powered various concept (Jaguar C-X75), prototype, and racing vehicles. It was also used in the Koenigsegg Regera, the Ferrari SF90 Stradale and S96GTB, Lamborghini Revuelto hybrid and the Lola-Drayson.[9] The company is investigating the potential for placing motors inside wheels, given that AFM's low mass does not excessively increase a vehicle's unsprung mass.[10] "

The fact that you CAN put it in the wheel doesn't mean it MUST to go in the wheel.

Yes but the wikipedia article is referencing YASA, the company in the featured article.

They’re investigating the potential for them to be placed inside wheels, but they aren’t at the moment, so my point stands.

I think they misspoke when they said "in" the wheel, but supercars can have a separate motor for each wheel, and the closer they are to the wheel the better the torque as it's not also driving a longer shaft. The smaller the motor, the closer you can get.

I guess if you can make the motor and a suitable reduction box lighter than the equivalent bearing and driveshaft combination you could make the suspension arms mechanically simpler.

By using motors at each wheel you'd eliminate the need for a differential, saving a good 40-50kg or so. Of course, if you kept the drive shafts and put the motor and reduction box in the middle, you'd be able to use inboard brakes and save a lot of unsprung weight!

I wonder if that would be legal, or if there is a regulation about where you can put your brakes?

I’ve generally assumed that brakes are in the wheel because they’re not all that massive, they get decent cooling airflow in the wheel, and they can produce enormous amounts of torque.

There are cars with inboard brakes, although not recently. From a packaging point of view putting them out at the wheel makes sense, since there's a lot of space you're not using otherwise.

It's hard to fit inboard brakes to front wheel drive cars because there's so little space but Citroën managed it with the 2CV and various derivatives, and the GS/GSA/Birotor family. They had an inline engine with a very compact gearbox behind, with the brake discs (drums, on very early 2CVs) right on the side of the gearbox.

You got lower unsprung weight and possibly more usefully the kingpin was aligned with the centre of the tyre, so when you steered the tyre turned "on the spot" rather than rotating through a curve.

Some old Jags and Alfas had inboard discs on the rear axle, which was of course rear wheel drive. They were a bit of a pain to get at.

Super pro comment, should be much higher.

it would be really interesting if it became possible to do electronic only breaks. I'm sure the regulatory system isn't there yet, but it would let you shave a whole bunch more parts and complexity

Interesting! But yes in axel in this case then

I get your skepticism and I know nothing about the field, but if the round thing in the press release picture isn’t designed to fit in a wheel, I’m confused. https://yasa.com/news/yasa-smashes-own-unofficial-power-dens...

Not necessarily, cf: https://lammotor.com/wp-content/uploads/2024/12/YASA-400R.jp...

From https://lammotor.com/yasa-axial-flux-motor/

the shape is due to the change to the motor layout: https://www.thedrive.com/news/why-axial-flux-motors-are-a-bi...

It’s currently designed for the axel for now as far as I’m aware.

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