3 ms·

Do the Tesla’s still have differentials then? It would be cool to eliminate those two but then you’d need a motor for each wheel I guess.

Negitivefrags 6y ago
They do for all the models currently on the road. In the future the Roadster and the Cybertruck both have 3 motors. The rear wheels both have one each, so presumably they can avoid the differential there.
chaboud 6y ago
Rivian has an independent 4-motor setup. It's a compelling case of extra parts allowing for simplicity. It also allows for the ever-entertaining tank turn: https://www.youtube.com/watch?v=yzwM8KE2L3I https://www.youtube.com/watch?v=yzwM8KE2L3I
sandworm101 6y ago
Differentials still have a place. They allow wheels to be perfectly balanced when negotiating corners. That can be done with independent electric motors, but never perfectly. Lot of little factors have to be considered in the software. For instance, as a car corners weight shifts, this causes the diameters of pneumatic tires to change slightly. A mechanical differential handles this tiny effect seamlessly. Independent motors on each wheel would have to sense, calculate and react to this via software. That is just one effect. There are also uneven road surfaces to deal with. Any slight error would result in one wheel dragging or trying to accelerate, resulting in instability or at least chewing through tire rubber. Differentials are cheap and reliable, most going for the lifetime of a car without any issue or even real servicing. They are likely the cheaper option than running multiple motors.
- mrfusion 6y ago
  Good point. What about simply powering only the outer wheel? It could look at the steering position to decide when to do that?
  - sandworm101 6y ago
    So long as you are happy giving up 1/2 of your traction, that would only solve corners if the steering wheel is moving. Say your right wheel hits a bump. Even with zero steering input that right wheel is traveling slightly further than the left wheel. (Up and over the bump is longer than the strait line driven by the left wheel.) There also also times when the steering wheel moves but the car remains strait (crosswinds). The further one looks down this rabbit hole, the more appealing a simple mechanical differential becomes.

Negitivefrags 6y ago

They do for all the models currently on the road. In the future the Roadster and the Cybertruck both have 3 motors. The rear wheels both have one each, so presumably they can avoid the differential there.

chaboud 6y ago

Rivian has an independent 4-motor setup. It's a compelling case of extra parts allowing for simplicity. It also allows for the ever-entertaining tank turn: https://www.youtube.com/watch?v=yzwM8KE2L3I https://www.youtube.com/watch?v=yzwM8KE2L3I

sandworm101 6y ago

Differentials still have a place. They allow wheels to be perfectly balanced when negotiating corners. That can be done with independent electric motors, but never perfectly. Lot of little factors have to be considered in the software. For instance, as a car corners weight shifts, this causes the diameters of pneumatic tires to change slightly. A mechanical differential handles this tiny effect seamlessly. Independent motors on each wheel would have to sense, calculate and react to this via software. That is just one effect. There are also uneven road surfaces to deal with. Any slight error would result in one wheel dragging or trying to accelerate, resulting in instability or at least chewing through tire rubber. Differentials are cheap and reliable, most going for the lifetime of a car without any issue or even real servicing. They are likely the cheaper option than running multiple motors.

mrfusion 6y ago
Good point. What about simply powering only the outer wheel? It could look at the steering position to decide when to do that?
- sandworm101 6y ago
  So long as you are happy giving up 1/2 of your traction, that would only solve corners if the steering wheel is moving. Say your right wheel hits a bump. Even with zero steering input that right wheel is traveling slightly further than the left wheel. (Up and over the bump is longer than the strait line driven by the left wheel.) There also also times when the steering wheel moves but the car remains strait (crosswinds). The further one looks down this rabbit hole, the more appealing a simple mechanical differential becomes.