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Tesla Model Y, Cadillac ELR, Rivian R1T, Chevrolet Volt, Spark EV
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Discussion Starter · #1 ·

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.
👍😎
 

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Locked diffs can and often do slip tires Although a fully agree that a 4 motor or EV motor attached to open diffs can likely never equal a fully locked rig. I’ve had 3 triple locked (land cruisers 60 and 80 and an g500) off roaders over the years and my current LX570 is double locked (center, rear). I think another limitation of EVs off road is the massive instant HP/torque, a Unimog, one of the best off roaders out there is <200 hp ~400 ftoh and it’s GVWR is >that of three R1Ts.
 

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I understand locking diffs, but understand why with quad motors and the ability to very accurately control wheel speed and power output to each motor they can't do a better job of simulating lockers. It probably can't be quite as good as lockers, but it seems like they should be able to get it closer. In respect to instant torque, it seems that over time they will likely provide better throttle mapping. I recently saw a newer out of spec video (don't remember which one) where he mentions that throttle mapping has improved since he has had his R1T. I don't have mine yet, but from what I've seen until the improvements are made this is going to be a very capable off roader but probably not a rock crawler.
 

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Tesla Model Y, Cadillac ELR, Rivian R1T, Chevrolet Volt, Spark EV
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Discussion Starter · #4 ·
I understand locking diffs, but understand why with quad motors and the ability to very accurately control wheel speed and power output to each motor they can't do a better job of simulating lockers. It probably can't be quite as good as lockers, but it seems like they should be able to get it closer. In respect to instant torque, it seems that over time they will likely provide better throttle mapping. I recently saw a newer out of spec video (don't remember which one) where he mentions that throttle mapping has improved since he has had his R1T. I don't have mine yet, but from what I've seen until the improvements are made this is going to be a very capable off roader but probably not a rock crawler.
The biggest downfall of the design is not it's attempts at mimicking a locked diff, but rather trying to replicate an open diff. On very slippery surfaces it always tries to power all Wheels (unlike a diff) which causes unpredictable, and often terrifying results.
 

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The problem with lockers is that they make it hard to turn because they don't allow the outer wheel to spin faster than the inner wheel. Therefore you engage them only for short periods of time when you are traveling mostly on a straight line. I would rather have 4 motors doing their thing 100% of the time than lockers doing their thing 0.1% of the time.
 
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