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Looks like the Tesla has an open diff with poor brake lock diff control, I think the lighting has an option for a locking rear diff wonder if they were using it

Looks like the Tesla has an open diff with poor brake lock diff control, I think the lighting has an option for a locking rear diff wonder if they were using it, looks like it. Interesting thing about the Rivian quad motor version is while it has full software control due to a motor per wheel, this can be a downside for crawling like this because it has no way to send torque from one side to the other, so if say only two wheels have traction its torque is cut in half and can actually struggle to move forward as its also a fixed gear ratio. Contrast this with say a Jeep wrangler that can have a locking transfer case with low range and locking diffs can send a lot of torque to a single wheel through torque multiplication in both the transmission and transfer case and everything locked up. Jeeps also have a decent brake lock diff even if you don't have lockers.

GenerWork 3y ago
>this can be a downside for crawling like this because it has no way to send torque from one side to the other I'm pretty sure that there'll eventually be some sort of LSD/locking programming for electric motors. Take the existing F-150 Tremor for example. It comes with a locking rear diff and a Torsen diff in the front axle. If you have a quad motor vehicle, someone could easily write a "locking rear diff" mode that simply has the rear motors turn at the same pace, and then have a "Torsen diff" mode for the front that will modulate the front motors just like a Torsen diff would.
- SigmundA 3y ago
  It's not about turning at the same pace, the side that has no traction cannot send its torque to the side that does without a mechanical connection. Each wheel is limited to the maximum torque of a single motor vs torque being sent to all wheels in a traditional single ICE engine with transfer case and lockers. You can see a quad motor Rivian performing worse than the new dual motor due this issue, the dual motor can use brake locking to send full torque from one side to the other, the quad motor cannot: https://youtu.be/I9J52zE5boc?si=Fn1KA6Mtb_FFTGDc&t=2652 https://youtu.be/I9J52zE5boc?si=Fn1KA6Mtb_FFTGDc&t=2652
  - deelowe 3y ago
    You just need motors large enough to break traction. After that, it's irrelevant. Doesn't seem impossible to me.
    - SigmundA 3y ago
      Yeah just need larger motors that can put out more torque which adds more cost and weight. Or you can have a way to connect each side with a locker or a single larger motor with brake locker control like dual motor vs quad motor Rivian's. Again the quad motor Rivian can be stalled on rock crawling due to lack of torque when multiple wheels lose traction. Electric motors have a lot of torque but EV drive trains are usually single speed so it must not have too much gear reduction for highway speed. A modern ICE offroad vehicle has a multispeed transmission with torque converter that greatly amplifies stall torque along with a transfer case that has a low range that multiplies even further. I would imagine when jeep does an electric production Wrangler it will probably have dual motors with lockers and may even have a 2 speed transmission for low range. Maybe they will even do like their Magento prototype and run a single large electric motor through a traditional transfer case and driveline.
jmtulloss 3y ago
I am no expert at this but I think the Rivian should perform comparably. The Rivian can do 908 lb-ft of torque. Like you say, that's divided up amongst the 4 wheels, so that's 227 lb-ft per wheel. The Jeep can do 260 lb-ft total. The Rivian weighs ~7200 lbs and the Jeep weighs ~5300 lbs. So, with only one wheel of traction you're right. If you can transfer all of that torque on the jeep with less than ~14% loss (which, I dunno, might be reasonable) then the Jeep has more "oomph". With two wheels, the Jeep is still figuring out how to distribute 260 lb-ft and the Rivian has 454. It's not close at that point.
- SigmundA 3y ago
  A Jeep can have over 100:1 gear ratio in low range with torque converter and transmission and axles, its can put 20,000 to 30,000 lbs/ft to the wheels a quad motor Rivian is a fixed 12.6:1 gear ratio so 11440.8 lbs/ft to the wheels max. Now have two wheels lose traction and you cut that down to 5720.4 lbs/ft at the wheels while a Jeep with lockers put the full 20k+ torque to any one wheel as needed.

GenerWork 3y ago

>this can be a downside for crawling like this because it has no way to send torque from one side to the other I'm pretty sure that there'll eventually be some sort of LSD/locking programming for electric motors. Take the existing F-150 Tremor for example. It comes with a locking rear diff and a Torsen diff in the front axle. If you have a quad motor vehicle, someone could easily write a "locking rear diff" mode that simply has the rear motors turn at the same pace, and then have a "Torsen diff" mode for the front that will modulate the front motors just like a Torsen diff would.

SigmundA 3y ago
It's not about turning at the same pace, the side that has no traction cannot send its torque to the side that does without a mechanical connection. Each wheel is limited to the maximum torque of a single motor vs torque being sent to all wheels in a traditional single ICE engine with transfer case and lockers. You can see a quad motor Rivian performing worse than the new dual motor due this issue, the dual motor can use brake locking to send full torque from one side to the other, the quad motor cannot: https://youtu.be/I9J52zE5boc?si=Fn1KA6Mtb_FFTGDc&t=2652 https://youtu.be/I9J52zE5boc?si=Fn1KA6Mtb_FFTGDc&t=2652
- deelowe 3y ago
  You just need motors large enough to break traction. After that, it's irrelevant. Doesn't seem impossible to me.
  - SigmundA 3y ago
    Yeah just need larger motors that can put out more torque which adds more cost and weight. Or you can have a way to connect each side with a locker or a single larger motor with brake locker control like dual motor vs quad motor Rivian's. Again the quad motor Rivian can be stalled on rock crawling due to lack of torque when multiple wheels lose traction. Electric motors have a lot of torque but EV drive trains are usually single speed so it must not have too much gear reduction for highway speed. A modern ICE offroad vehicle has a multispeed transmission with torque converter that greatly amplifies stall torque along with a transfer case that has a low range that multiplies even further. I would imagine when jeep does an electric production Wrangler it will probably have dual motors with lockers and may even have a 2 speed transmission for low range. Maybe they will even do like their Magento prototype and run a single large electric motor through a traditional transfer case and driveline.

jmtulloss 3y ago

I am no expert at this but I think the Rivian should perform comparably. The Rivian can do 908 lb-ft of torque. Like you say, that's divided up amongst the 4 wheels, so that's 227 lb-ft per wheel. The Jeep can do 260 lb-ft total. The Rivian weighs ~7200 lbs and the Jeep weighs ~5300 lbs. So, with only one wheel of traction you're right. If you can transfer all of that torque on the jeep with less than ~14% loss (which, I dunno, might be reasonable) then the Jeep has more "oomph". With two wheels, the Jeep is still figuring out how to distribute 260 lb-ft and the Rivian has 454. It's not close at that point.

SigmundA 3y ago
A Jeep can have over 100:1 gear ratio in low range with torque converter and transmission and axles, its can put 20,000 to 30,000 lbs/ft to the wheels a quad motor Rivian is a fixed 12.6:1 gear ratio so 11440.8 lbs/ft to the wheels max. Now have two wheels lose traction and you cut that down to 5720.4 lbs/ft at the wheels while a Jeep with lockers put the full 20k+ torque to any one wheel as needed.