5 ms·

It doesn't have differentials at all ... Each wheel has it's own motor.

almost_usual 3y ago
I see so slips are impossible to prevent, this seems like a big limitation for serious off roading. https://www.rivianforums.com/forum/threads/quad-motor-vs-locking-diff.12010/ https://www.rivianforums.com/forum/threads/quad-motor-vs-loc... The Tacoma Off Road Crawl Control is somewhat similar but uses ABS to prevent slips. It does come with a rear locker though.
- abenga 3y ago
  I'm not an expert here, but what stops four wheels from all rotating at the same speed with independent motors?
  - almost_usual 3y ago
    From the link: > If the axles are not physically tied, there is no way for any of the four wheels to know how much traction it actually has until it breaks free. Then, of course, it knows "too much" torque and it can apply traction control. But the damage is done. It has broken free, and any negative consequences have already happened prior to the computer being able to make any further calculations. > Again, if physically locked together with large gears and drive shafts, there is no possible way for one wheel to break free in that manner, unless of course something is broken.
  - bluGill 3y ago
    All four wheels rotating at the same speed is the normal case: straight line driving on good pavement. The real question is can all the wheels go to zero traction at the same moment and thus the computer thinks all is well. I think the odds of that are low enough to not worry about.
    - callalex 3y ago
      Traction control systems also use accelerometers and gyroscopes, so the scenario you describe is not possible.
- Daneel_ 3y ago
  Well, yes, but you can also sense which ones are turning slower and just increase the torque to those. Locking diffs simply provide torque to the wheels with grip, which is exactly what one motor per wheel can do too. There’s no difference in the real world, and in fact performance is even better because there’s no turning circle penalty from having a locked diff.
  - almost_usual 3y ago
    > Well, yes, but you can also sense which ones are turning slower and just increase the torque to those. From the link: > If the axles are not physically tied, there is no way for any of the four wheels to know how much traction it actually has until it breaks free. Then, of course, it knows "too much" torque and it can apply traction control. But the damage is done. It has broken free, and any negative consequences have already happened prior to the computer being able to make any further calculations. > Again, if physically locked together with large gears and drive shafts, there is no possible way for one wheel to break free in that manner, unless of course something is broken. Some other interesting tests by an R1T owner. https://www.rivianforums.com/forum/threads/quad-motor-vs-locking-diff.12010/post-270978 https://www.rivianforums.com/forum/threads/quad-motor-vs-loc...
    - CPLX 3y ago
      I mean, doesn't the set of computer controlled individual motors completely and totally contain all scenarios presented by a locked differential? Specifically, wouldn't one line of code that says "never ever ever turn this wheel faster than this other wheel" be totally and completely indistinguishable from having the wheels on the same axle, as far as the physical world is concerned?
      - shkkmo 3y ago
        That's not how electric motors work. You can measure the speed and adjust the power going to the motor if you go over or under that speed. The lower latency that this cycle has, the better, but it can never go to zero like with physically connected wheels.

I see so slips are impossible to prevent, this seems like a big limitation for serious off roading. https://www.rivianforums.com/forum/threads/quad-motor-vs-locking-diff.12010/ https://www.rivianforums.com/forum/threads/quad-motor-vs-loc... The Tacoma Off Road Crawl Control is somewhat similar but uses ABS to prevent slips. It does come with a rear locker though.

abenga 3y ago
I'm not an expert here, but what stops four wheels from all rotating at the same speed with independent motors?
- almost_usual 3y ago
  From the link: > If the axles are not physically tied, there is no way for any of the four wheels to know how much traction it actually has until it breaks free. Then, of course, it knows "too much" torque and it can apply traction control. But the damage is done. It has broken free, and any negative consequences have already happened prior to the computer being able to make any further calculations. > Again, if physically locked together with large gears and drive shafts, there is no possible way for one wheel to break free in that manner, unless of course something is broken.
- bluGill 3y ago
  All four wheels rotating at the same speed is the normal case: straight line driving on good pavement. The real question is can all the wheels go to zero traction at the same moment and thus the computer thinks all is well. I think the odds of that are low enough to not worry about.
  - callalex 3y ago
    Traction control systems also use accelerometers and gyroscopes, so the scenario you describe is not possible.
Daneel_ 3y ago
Well, yes, but you can also sense which ones are turning slower and just increase the torque to those. Locking diffs simply provide torque to the wheels with grip, which is exactly what one motor per wheel can do too. There’s no difference in the real world, and in fact performance is even better because there’s no turning circle penalty from having a locked diff.
- almost_usual 3y ago
  > Well, yes, but you can also sense which ones are turning slower and just increase the torque to those. From the link: > If the axles are not physically tied, there is no way for any of the four wheels to know how much traction it actually has until it breaks free. Then, of course, it knows "too much" torque and it can apply traction control. But the damage is done. It has broken free, and any negative consequences have already happened prior to the computer being able to make any further calculations. > Again, if physically locked together with large gears and drive shafts, there is no possible way for one wheel to break free in that manner, unless of course something is broken. Some other interesting tests by an R1T owner. https://www.rivianforums.com/forum/threads/quad-motor-vs-locking-diff.12010/post-270978 https://www.rivianforums.com/forum/threads/quad-motor-vs-loc...
  - CPLX 3y ago
    I mean, doesn't the set of computer controlled individual motors completely and totally contain all scenarios presented by a locked differential? Specifically, wouldn't one line of code that says "never ever ever turn this wheel faster than this other wheel" be totally and completely indistinguishable from having the wheels on the same axle, as far as the physical world is concerned?
    - shkkmo 3y ago
      That's not how electric motors work. You can measure the speed and adjust the power going to the motor if you go over or under that speed. The lower latency that this cycle has, the better, but it can never go to zero like with physically connected wheels.