[benj111]

Why not?

You'd have an added complication of making the shock absorber the pivot point, and attaching the motor to the top point. Or having a separate pivot point where the motor or wheel can slide up and down.

This does raise the question of why not just attach the motor straight to the wheel.

The standard response to that is a hand wavey "unsprung mass". But has it actually been tried and shown to be an issue?

[tlb]

Unsprung mass sucks. You don’t notice on smooth surfaces, but if you are cornering on a rough surface the wheel ends up losing contact with the ground after each bump. It’s extra-dangerous when its the rear wheels because the car can spin out.

[hwillis]

It's not unsprung. The wheel and gear bit are the only unsprung parts; think of it like the motor attaching directly to the wheel bearing, and the wheel is able to move vertically on the bearing.

I think this only works with RWD, because the turning wheels can't be sprung without also having to rotate the springs.

It would be a better suspension (closer to racing suspensions) than standard, because wheels wouldnt toe in/out when they moved down/up. Looks expensive as hell though

[schiffern]

tlb was replying to this part:

"This does raise the question of why not just attach the motor straight to the wheel. The standard response is ...unsprung mass"

[hooby]

Well, if the motor is unsprung mass, you no longer need this contraption at all, and you can just directly connect the motor to the wheel...

So, that's probably not it.

[dist-epoch]

I'm no mechanical expert, but I wonder how you prevent damage to the motor if the wheel encounters an obstacle when it tries to rotate (against a curb for example) or if it's forced to rotate by an exterior force.

[benj111]

Cars already have traction control, and there's probably a thermal cutout already in the motor.

[DennisP]

The wheel can move up and down relative to the motor, so you can still attach a shock absorber to the wheel, without the motor being involved. The video shows this at 2:36.

[benj111]

Yes my point is, why have the complication of this set up at all.

[DennisP]

To me it doesn't seem any more complicated than a pair of CV joints.

Benefits according to the article: "reduced packaging size, improved ride quality, greater durability and, importantly, increased efficiency."

[consp]

> The standard response to that is a hand wavey "unsprung mass". But has it actually been tried and shown to be an issue?

Afaik with high performance motors, if you want optimal performance and space efficiency you take the unsprung mass for granted and move everything in wheel and try to reduce the mass as much as possible. As a bonus you do not need joints, just a planetary gear system.

[benj111]

Why only high performance though.

A motor per wheel simplifies everything.

No diff, no CV joints, you don't need this, just a simple planetary gearbox.

You gain space, lower manufacturing costs (theoretically, assuming multiple motors doesn't offset the other cost reductions, although as you could base a 2wd and 4wd high performance version on the same motor, that's an even harder case to make).

[lstodd]

Everyone says "unsprung mass" but you also have to provide cooling without ingesting all the dirt and water off the road. It's not that simple.

[benj111]

Brake lines are a solved problem. Water lines wouldn't be any more difficult. If air cooled it could be a sealed unit.

[deeg]

I've been under the impression that putting the motor on the wheels increases gyroscopic forces which can cause handling problems.

[benj111]

It isn't rotational mass though, just unsprung.