[husam212]

Maybe the motor is supposed to turn with the wheel, that doesn't sound like a good idea.

[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.

[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.

[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.

[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.

[deeg]

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

[justinclift]

That'd make the motor the pivot point. No idea if that's good or bad though. :)