Quad motor vs locking diff

[White Shadow]

That's literally the entire point of a locked differential and exactly how it works.

You should stick to topics you may be suited better for. May I suggest crocheting?

Nothing I said was incorrect. So go ahead and try again.

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[White Shadow]

... And torque can even be added to the other side due to rotational inertia of that Mass (flywheel effect).

Sir, I certainly am not making any attempt to flame, but you advance flawed and incorrect assumptions, and then simply want to argue about them for the sake of argument.. I'm not sure how constructive that is to those really interested in understanding the principles.

Physics isn't that complicated. Wheels don't rotate by magic. It takes torque to make that happen. Yes, even if they are in the air. What's the weight of the rotating assembly? IF you don't know, then take a guess. Once we know that, we can make a reasonable assumption on the requirement to rotate it.

 

[zipzag]

Physics isn't that complicated. Wheels don't rotate by magic. It takes torque to make that happen. Yes, even if they are in the air. What's the weight of the rotating assembly? IF you don't know, then take a guess. Once we know that, we can make a reasonable assumption on the requirement to rotate it.

Physics may not be complicated but the weight of a rotating wheel system is not part of the calculation of the torque needed to keep it moving.

 

[R.I.P.]

Physics isn't that complicated. Wheels don't rotate by magic. It takes torque to make that happen. Yes, even if they are in the air. What's the weight of the rotating assembly? IF you don't know, then take a guess. Once we know that, we can make a reasonable assumption on the requirement to rotate it.

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[R.I.P.]

Physics may not be complicated but the weight of a rotating wheel system is not part of the calculation of the torque needed to keep it moving.

You are of course right, but this guy clearly does not have a great grasp on the subject, and is only here to argue for the sake of argument. I learned that before, and am sheepish for having forgotten it.
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[Zybane]

Yikes, even more testing showing the Rivian is hobbled in a lot of scenarios. Floored on a flat surface with three wheels on rollers... and the 4th motor/wheel isn't even/barely doing anything. Pretty awful/SUPER conservative programming.

 

[HaveBlue]

It actually did ok and as expected. I'd say it's similar or a bit better than the first generation Toyota ATRAC system from the early 2000s. The newer ATRAC includes crawl control that works at slower wheel and engine speeds. The early ATRAC also required some speed in the form of 1500 rpm engine speed. Still none of the ATRAC systems, and Toyota makes the best one, come even close to locking diffs. No where near the same league. You'll hear that from anyone who rock crawls real rigs on serious trails.

 

[zefram47]

It actually did ok and as expected. I'd say it's similar or a bit better than the first generation Toyota ATRAC system from the early 2000s. The newer ATRAC includes crawl control that works at slower wheel and engine speeds. The early ATRAC also required some speed in the form of 1500 rpm engine speed. Still none of the ATRAC systems, and Toyota makes the best one, come even close to locking diffs. No where near the same league. You'll hear that from anyone who rock crawls real rigs on serious trails.

So far, the Rivian performs nothing like ATRAC. I still have hope they can fix their off-road calibration, but to say it's not great right now is an understatement.

 

[IPTV65]

Yikes, even more testing showing the Rivian is hobbled in a lot of scenarios. Floored on a flat surface with three wheels on rollers... and the 4th motor/wheel isn't even/barely doing anything. Pretty awful/SUPER conservative programming.

I saw that too. That’s just poor programming in my opinion. 3 spinning one not. Unless it fell off you can use the one not spinning to ascertain lack of forward motion. Just throw a little torque that way to achieve equal rotational speed and see what happens. What’s the harm if that one spins too? A vehicle with lockers will gladly spin all 4 while going absolutely nowhere. Of course I have to be missing something. It could not possibly be that easy.

 

[HaveBlue]

You have to keep in mind that this vehicle isn't 4wd even. It's all wheel drive. It doesn't have a center lock that evenly divides torque front to rear. It has to be simulated in software. The dual motor won't have that either so even adding locking diffs to that will still require software to help out. Rivian has a full plate to catch up where slow traction is concerned. High speed rally it's likely an excellent system.

 

[MM in South TX]

I read the first couple of pages and the last page of this thread. Can someone explain to me the early comments that claim that software can not overcome the lack of a locking differential? It seems like software could measure spin and adjust braking and torque to specific wheels. I know that is already done in many vehicles.

Not sure how it works, but my Lightning has electronically locking differentials, in a dual motor configuration.

 

[Zybane]

Rivian is very conservative with their driveline tuning IMO. They don't want a bunch of driveline warranty repairs. Main reason why they eliminated "tank turn". Telling one motor/wheel to turn a particular RPM "at all costs", aka "locked differential", put's an incredible amount of strain on the driveline for that one wheel.

Rivian only has 225 ft/lb of Torque per wheel as it has no locking differentials/transfer case, which means it cannot use any of the other motors to turn that particular wheel. If you get that one wheel say stuck in-between two rocks or up against a ledge, it hits its maximum torque load and then stops turning. Why you see so many Rivians off-roading, even with the pedal floored and the truck doesn't move.

It's literally "tapping-out", and the main reason Rivians will never be able to do more than light/moderate off-roading. But to be fair, I think that was their planned limit all along.

 

[HaveBlue]

The problem is that the software isn't smart enough to use hardly any of the torque from that one wheel with traction and refuses to at that. 225ftlb is double what a 1985 4runner has and they are rock crawling monsters. As hard as that rivian pulls from a stop light, it should be able to get some drive off one wheel. After all conserve uses two safely.

 

[AlexF]

The problem is that the software isn't smart enough to use hardly any of the torque from that one wheel with traction and refuses to at that. 225ftlb is double what a 1985 4runner has and they are rock crawling monsters. As hard as that rivian pulls from a stop light, it should be able to get some drive off one wheel. After all conserve uses two safely.

But… that 1985 4Runner has a transmission, low range transfer case, and differentials to multiply torque.

 

[HaveBlue]

But… that 1985 4Runner has a transmission, low range transfer case, and differentials to multiply torque.

So does the rivian according to the EPA filing and the tires would fly apart at motor speeds of 6000 rpm if it were direct drive not to mention Max rpm is 16000.

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