Moosehead wrote: ↑Mon Dec 20, 2021 9:53 am
In Rivian’s case, with a motor at each wheel, there is no center driveshaft/transfer case/differential. Note the early videos showing the R1T doing Hell’s Gate and other OR efforts are also using their own stock Pirelli Scorpion spec tires which are not nearly as aggressive or capable OR rubber but the incredible traction afforded by Rivian’s unique drivetrain still shows remarkable prowess OR. This, plus 4 wheel adjustable indy air suspension provide for some impressive OR capabilities, of which they are just scratching the surface. OR gearing can simply be customized by ECU vs mechanical trans, axles, and lockers.
See Jalopnik’s description of the Rivian chassis and OR capabilities here:
https://jalopnik.com/a-ridiculously-det ... 1847749837
Pic of skateboard chassis below, the mid frame is all battery cells providing for clearance, low weight distribution, and in cabin space.
This issue with the four motor approach, and Doug’s video showed this perfectly, is that it’s extremely rare that all four tires have the same amount of loading on them. In a vehicle with lockers, all four tires have to spin at the same speed. So if one tire has tons of traction, but the other three do not, the three without are not going to sit there and spin like crazy. Instead that tire with traction will pull the vehicle up as it will be receiving all the torque. This allows for finesse, as the driver has far better control. It also means the vehicle won’t lose lateral stability.
With the Rivian, this is not the case. Each tire is being sent the same amount of torque, but the only thing controlling wheel speed is the computer. But all the computer does is decrease the torque going to wheels that are spinning. The one tire with traction is still stuck there without enough torque to pull the vehicle up. So he kept having to give it more throttle. But then once it got up that one spot, the amount of throttle way was too much so everything started to spin like crazy.
As for gearing, no. This can’t be done via an ECU. You cannot program in mechanical leverage. One of the big issues with current electric vehicles (except the 4xE) is that they do not have low gearing. This means two things. One, the motor spends a lot of time at very low RPM where it is extremely inefficient. The current draw is insanely high at zero RPM. Sure they make tons of torque there, but at the cost of crazy high battery consumption. In normal driving though they are only there for a split second. Off road, they are there most of the time. The other side effects of this is you have to rely heavily on the computer to control vehicle speed when traction is lost, which is bad. In my Wrangler for instance, I know in first gear, low range I am basically redlining at 9mph. If I break traction, I know my wheel speed isn’t going to go nuts. However in the Rivian, if you disabled traction control, the tire could quickly spin up to 100mph. Meaning if it then caught traction, parts are going to explode. And I know Rivian does not allow you to turn it off. Which brings up the issue of how do you get through obstacles that require when spin?
As for the suspension, as I note above, on the street it is great. And it does show some interesting characteristics off-road. It is also however extremely complicated with all the cross corner lines. And if really used off-road, it is unlikely it would hold up.
Rivian seems bent on trying to make the truck a Jack of all trades. They keep trying to market it as the truck that does everything perfectly. And if anybody says anything bad, they attack them for it. They are hurting themselves by setting expectations unrealistically high.