Tesla Model Y, Cadillac ELR, Rivian R1T, Chevrolet Volt, Spark EV
Good review, illustrating very well why quad motors can't really compete with full locking diffs. It is interesting to see in the comments that people believe this can be "fixed" with software updates. I guess it is just a factor of people not understanding the technology.
A traditional four-wheel drive with fully locked diffs turns all four wheels at exactly the same speed. One wheel can never, and this is the point that is so very important NEVER slip. Any slip can mean falling off a rock and impaling your truck. Any slip starts to create holes that you have to dig yourself out of. When it is critical that you don't slip any wheel, four wheels locked into identical rotation speeds can never be approximated by a quad motor or software.
While this creates a handicap the quad motor Rivian can never overcome off-road, it has a similar handicap on road. When conditions become super slippery, (snow and ice is an example), a traditional four wheel drive can lock both front and rear axles together while not locking the differentials. In this mode there are at least two wheels at any given time providing lateral stability while the other two attempt to either increase or decrease speed. Again, four disconnected wheels on motors and software can never really approximate this very important ability.
I doubt that Rivian will ever admit that there is more than just a cost savings motivation behind the new dual motor version. As cool as the quad motors are, and as useful as they are in some circumstances, they really do carry some very basic handicaps.
Thank you Kyle for a decent demonstration of at least the first concept.