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Comment by lelanthran | Hacker News Reader

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 some marketing department numbers or something. 630 kw is roughly 850 horsepower.

There's a whole lot of marketing speak, finger waggling, and wishful thinking in what I am seeing here.

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.

Well, you can already buy one: https://www.vergemotorcycles.com/

Well that is interesting.

I still have my doubts, but I wish them luck. I've always wanted to get Kenada's bike.

> 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/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?

A regular wheel is about 12kg bringing wheel+tire to ~25kg

At these weights, I suspect the vehicle won't handle as well as a vehicle with the motor offboard.

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.

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.

I'm thinking about the motorcycle motor. If they're really lighter than competing motors, I don't see the downside of using them like a traditional motor, taking the weight savings, putting it inside a sealed cavity, and coupling it to a driveshaft. Simplifies some of the other problems with sealing and bearings mentioned elsewhere, avoids unsprung mass.

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