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Comment by seltzered_ | Hacker News Reader

FWIW, there was recently a now-defunct car company (Lordstown motors) that utilized an in-wheel motor from the company Elaphe (https://in-wheel.com/en/technology/#in-wheel-motor-technolog...)

I think the tradeoff is between more flexibility & fewer parts (no cv joints) but possibly more rolling resistance.

But watch the video, this uni-wheel thing is different. It isnt an in-wheel motor, more of a cv-joint alternative?

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I'll be interested to see if the Elaphe in-wheel motors are designed into a high ground clearance 4WD. The site says added weight 25-65kg but maybe that is two motors for 2WD? A grunty 4WD tyre like a 33 inch (33/12.50R20) might weigh 33kg per tyre (not sure if rim weight), so the additional unsprung weight for the motor is comparatively reasonable per wheel? In-wheel would allow the suspension to be designed for much better clearance (since no shafts). Tyre might have a speed rating of Q (99mph).

Pretty sure I measured a 33" BF Goodrich MT (mud traction) tire on an aluminum 15x8 wheel at 93lbs. However, it was about 25 years ago so memory's probably a bit fuzzy.

Is Lordstown defunct?

As far as I know, this Czech company uses in-wheel motors:

https://spartan.mwmotors.cz/ev-traditional-technologies/

Looks like they already abandoned that idea: https://mwmotors.cz/luka-ev-traditional/

Interesting, I wonder what the technical reasons were for the change. It has gone this way with pretty much every hub motor concept that I've seen so far, either they don't make it of the drawing board, or they end up abandoned at the prototyping stage. The GP had me wondering if someone had actually managed to conquer it but alas that doesn't seem to be the case. It's a neat little car though, reminds of the Daihatsu Copen that I had at some point.

unsprung weight is what every engineer who looks at a hub motor will think. The less of that the better. Engineers would love to move the brakes off the wheel (there are safety reasons not to, but it would make the car handle notably better if you did)

Citroen DS/ID had that, SM as well. CX and XM did not.

Don't even need to be an engineer just go ride some nice bikes, it is an amazing and very tangible lesson in the cost of unsprung weight.

Yeah, it’s not a hub motor, so the unsprung weight should be a lot less.

unsprung weight I believe is also a big issue with hub motors esp as you get up to car size at speed

It is the issue for in-hub motors. Solve that one and the world will beat a path to your door and shower you with money.

The other issue is that potholes my get quite expensive.

Yes, the impact from a pothole can be substantial. Having an upset alignment is one thing, damaging the guts of an in-wheel motor is a totally different picture. But: when properly packaged and lightweight enough I think that is a secondary concern, you can design with that in mind given that it is more or less predictable from which direction and with which magnitude such an impact would happen. But every pound counts and the shocks+spring will have to be matched to the increased weight.

Have you got a source. Everyone mentions this, but I've never come across anyone trying and failing.

Motor scooters have unsprung motors, the motor is a significant proportion of the mass.

Motor scooter motors weigh a fraction of what the equivalent motor for a car would weigh, and it's exactly the problem:

The issue is that it scales poorly, unsprung weight is bad enough that on some cars the disc brakes live 'inboard' on the front wheels (older hydraulic suspension cars).

Essentially the larger the unsprung mass the bigger the hit every time the road surface irregularities cause the wheels to move relative to the vehicle body. The larger the mass the more energy gets imparted, and the more energy that gets imparted the bigger the impact and all that energy then needs to be absorbed so you'll need a stronger (and heavier) suspension system, roughly half of which is unsprung mass!, and a larger battery to compensate for the losses in the suspension which also adds weight (harder suspension -> bigger range but less comfortable ride). So it feeds back on itself and that's why it scales so poorly.

I can sort of buy this at the upper end. But a small car with 4 relatively small motors with normal tyres v a range rover with run flat tyres and massive disc brakes?

In a small car it could work, but you'd be very much limited in power and weight.

See upthread links and subsequent updates

https://news.ycombinator.com/item?id=38485097.

Note that more unsprung weight has other effects as well, such as poor handling because the wheel bounces higher and so will be out of contact with the road for a longer time when it encounters an obstacle. If you think of the weight of the wheel as the weight on a pendulum it is easy to see why that would affect the period of the swing.

You can buy a car powered with in-wheel motors here:

We have developed the first production car to use in-wheel hub motors. https://mwmotors.cz/luka-ev/

This car maybe too, as far as I understand it. A Russian UAZ on steroids: https://www.youtube.com/watch?v=RCOf_33C1qc

815 Kg curb weight, aluminum chassis. It makes sense for a vehicle with that form factor (2 seater little sports car) but you can't really compare it with a full sized sedan, and note too that it has a tiny battery pack (22 KWh), range is 'unofficial' 300 Km and likely will be adjusted down based on weight/pack size. The four motors together are less than half the rated power of what you'd find in a more conventional (is there such a thing already?) EV. But with that light total weight it will be a zippy little car anyway (most EVs are over-powered for their weight).

Still, very impressive achievement and a nice testbed for this kind of tech, it may also make sense for motorcycles and for vehicles that are not meant for highway use.

What is the advantage of in-wheel motors?

That you save on a whole bunch of linkage and drive train components, four wheel drive without the associated complexity, that you can integrate the wheels, motors and brakes, cleaner airflow under the car and that the system as a whole can be lighter weight than the same package with motors near the centerline of the car, so you get somewhat better range. It also gives more space for batteries and/or more storage space. That's why manufacturers will keep trying to get this done, if they can get it to work cost effectively and without impacting that unsprung weight too much it will give them an advantage.

"cleaner airflow under the car"?

Why should the airflow be cleaner?

Because that's automatically better range, cleaner airflow is less drag. That's why cars have all of those underbody skirts, it improves their mileage (and helps with not fouling up the more sensitive bits).

I think they mean smoother or less turbulent airflow, not cleaner in the sense of less pollution.

That Luka has some pretty interesting tech and is so sharp-looking. I hope it's a massive success.

Gorgeous little car! Reminds me of the sports cars of the 50's and 60's. But they apparently dropped the hub motors.

The height of that little sports car reminded me of the ultra-low-height 1960s Lotus Europa (first version) - one didn't so much exit it as roll outwards from it.

I've had a kei-car sized sports car that was a hoot to drive but it felt like putting on gloves just to get in.

Bummer. Like Mazda’s experiment with the Wankel engine it would have been very cool to see the results

Well, they did make them. I suspect that the safety concerns were the main issue (less road contact compared to inboard motors).

There's another startup, Aptera, which is ostensibly still working towards producing a vehicle using Elaphe hub motors. Interestingly they are efficiency focused so I wonder how the motors are working out for them in that respect.

Very well in fact, you have to look at the whole drivetrain efficiency, not just the motor. Elaphe has a webinar on this topic on their youtube channel, look it up.

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