Quad motor vs locking diff

[White Shadow]

One additional thing I've been wondering about. Engineering explained did a video on locking diffs but...

The R1T's power is split between 4 motors. That's 200hp/225lb tq per motor. In the event of a slip you end up relying solely on the motors that have traction. 3 wheels=600hp/675lb, 2=400/450, 1=200hp/225lb tq right?

With a locking diff, you get most of the power (*driveline loss?) to a single wheel according to the video.

So if we take a F-150 Lightning with dual motors at 580hp/775lb or 390hp/387lb per motor. When it locks you still get power from both motors. 3 wheels = 580hp/775lb, 2 wheels = 390hp/387lb, 1 wheel = 390hp/387lb.

Which would mean despite the significantly less power it is actually able to put down similar power and in some cases more because of the configuration. I'm not sure if I'm understanding that correctly, and don't off road - just trying to understand.

With a truly locked differential, you're splitting the available toque between two wheels. You'll never get it all to one wheel on a locked differential.

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[White Shadow]

I'm reading the words you wrote. And write again above.

First you don't *know* that "it would be easy to "change" - or fix.

Secondly, you don't have any idea what the implications *might* be to make the "easy" change in software - in context of the problem as it is defined by the vehicle - as it sits. But you continue to ignore this as it relates to the multiple issues at hand. Preferring to (now) cherry pick the problem so that you can insist on the solution you *believe* , perhaps correctly to be "easy".

And, as you have now been told by several others (again), the very real problem depicted in Kyle's video is only one of issue that the current implementation of software/hardware does not adequately address - for some people, in some situations.

The bottom line is , regardless of the language used, you have implied over and over again that the problem is trivial and up until now could be simply "fixed" with a software tweak. Now the word is "changed" and applies to only one of the problems.

Tomorrow the word will be "improved". And my guess Rivian will indeed improve on these and other issues. By enough? Who knows. I for one sincerely hope so. But it *may* not be trivial.

Just because tech has advanced very quickly over your lifetime does not necessarily mean the environment of the truck and the tech that can be readily applied will solve the issues present. "Past performance does not guarantee future results."

This whole discussion reminds me of an old, tired joke about the most genius invention. In variations many great things are proposed. Then someone suggests the "thermos" (yesterday's yeti cup). The reason given? "It keeps cold things cold and hot things hot. How does it know?"

Physics at work....

Call it whatever you want, but my opinion is that it's an easy fix. The software is already written for the vehicle to behave the way it does....and that can be easily changed in the software. I'm not saying that there aren't other considerations (such as the overheating I mentioned earlier), I'm simply saying that the behavior can be changed via software because that's what's happening currently.....it's not mechanical like a traditionally built vehicle.

 

[R.I.P.]

You can't move past an issue that's the root cause of the problem. Until Rivian changes the behavior of it's quad motor design, then it will never be comparable to today's other "offroad capable" vehicles. That's my whole point.

The other issue you mentioned did indeed seem like there was no torque available....but we know that isn't the case with these high-torque electric motors. What I suspect is happening is that the vehicle is intentionally limiting torque to the motors for whatever reason. It might be to keep the motors from overheating, who knows? I'll tell you this---I did read an article recently that Rivian is building a gearbox to enable torque multiplication through gearing instead of relying on the motors alone. Did anyone catch that article? Very interesting....

I did read about the crawler gearing they're looking at offering. Frankly, it blew my mind. It has to be bolted on, and then the vehicle is not highway capable until you switch it back to stock gearing. How this is an improvement to the lever in traditional vehicles that can drop you to low range and back within seconds is quite beyond me.
?

 

[R.I.P.]

With a truly locked differential, you're splitting the available toque between two wheels. You'll never get it all to one wheel on a locked differential.

Well, that's not true. If a differential is locked, and one wheel is in the air, then yes, all torque is going to the one with traction.

If you are having trouble visualizing why this is the case, consider this:

When a differential is locked, it is as if you have one single axle that drives both wheels. If you put 10lbs torque to that axle, you have 10lbs to the axle, 10lbs to the ground, which can be split between the wheels. If one wheel is lifted off the ground, you still have the same Force going to the ground, it is just on one wheel instead of two. The wheel in the Air does not "dissipate" any power, it has to go somewhere.

Does that help?

 

[White Shadow]

I'm not reading 20 pages of this thread to get to this point but as a former Jeep owner (will own one again in the future once the 4xe isn't stupid expensive) who has taken it off roading in a wide variety of terrain, the issue isn't differentials or wheel speed. A lot of the issue is that even though the R1T has 830hp...each wheel only has about 210hp. If one wheel has grip, your 210hp is all you got to move your 7k lb truck up and over an obstacle. With locking diffs, you get all the motor's torque and power to one wheel. Also, low range helps a lot.

I've taken my Jeep through some serious stuff and can count on one hand the number of times I've used the lockers. Top of the World, no lockers. Hell's Revenge, no lockers. Poison Spider, no lockers. Imogene Pass, no lockers. Black bear pass, no lockers...etc. The big things that are needed for effective off roading is articulation and tires. The Pirelli's that come stock aren't great and the articulation of a R1T is nowhere near the same as a Jeep Rubicon with the sway bar disconnected. Having a wheel on the ground is far more important than a locked diff for a variety of reasons.

Lastly, I don't EXPECT the Rivian to be anywhere close to as good as a Jeep off road. It's not at all meant to be that way. The Rivian is 1000000000000000000000000000x better on road than a Wrangler which is where the vast majority of them will live. It certainly can go off road in moderate situations but I doubt you'll see any Rivians traversing the Rubicon trail anytime soon. The Wrangler gives up a lot for being an off road beast, the majority of what it gives up is in on road behavior. The Rivian trades that off road performance for better on road performance.

So HP doesn't really mean anything at all. It's the torque that matters. And electric motors make great torque from essentially the moment they start spinning.

I agree that articulation is key, since a wheel in the air isn't going any good. Lockers only help in certain situations, not all offroad situations. In many cases, you'd want action similar to a limited slip diff, meaning constant transfer of power between wheels on the same axle.

With a quad motor set up, the potential capability is the best possible capability if it's controlled properly. You cannot get any better than having a motor at each wheel, but again, it has to be controlled properly. Rivian isn't meant to compete with a Wrangler....it's mean to compete with something like a Grand Cherokee. And Grand Cherokees can be quite capable, so Rivian should really aim for that level of offroad performance. Maybe in the future they'll come out with something like a Wrangler or Bronco competitor, but not with their current R1S &R1T

 

[White Shadow]

Well, that's not true. If a differential is locked, and one wheel is in the air, then yes, all torque is going to the one with traction.

If you are having trouble visualizing why this is the case, consider this:

When a differential is locked, it is as if you have one single axle that drives both wheels. If you put 10lbs torque to that axle, you have 10lbs to the axle, 10lbs to the ground, which can be split between the wheels. If one wheel is lifted off the ground, you still have the same Force going to the ground, it is just on one wheel instead of two. The wheel in the Air does not "dissipate" any power, it has to go somewhere.

Does that help?

The wheel in the air is still getting turned, so some torque is being consumed to turn that wheel/hub/axle, etc... Wheels don't turn on a locked axle without torque being applied.

 

[White Shadow]

Electronic traction control has been around for at least 20 years on 4Wheel drives. It is still no better than a limited slip differential. Doesn't matter if the vehicle is diesel powered or electric. You can muscle your way through obstacles with it but inevitably you will break something. Beam axles cantilever weight to the opposite side unlike IFS/IRS but in the end a locking diff always takes you further off road.
I've owned solid axle open diff vehicles and they go amazing places. I've also owned locked trucks with lockers front and rear. They are beasts and Kyle's video would qualify as the road that leads to the trail for them; not the actual trail.
On occasion I've shifted into 4Lo on my current vehicle but forgotten to lock the transfer case center leaving it in all wheel drive low range with the traction control struggling like crazy; similar to this video. With it locked it behaves better of course but locking the rear axle changes the whole game immediately. Those who aren't Web Wheelers just understand this.
Unfortunately, Kyle was actually driving in the worst possible way for traction control to function. Letting off the throttle right when it started moving or even worse stepping on the brakes. Traction control designed for off road doesn't work at zero wheel rpm. On a gas powered rig, the best is to just maintain 1500 engine rpm steady through the obstacle. Subconsciously he realized he was going to break something (bumper, undercarriage, etc) using the traction control.

I agree with that, but there's no reason to have to drive an EV in the same manner as an ICE with traction-based limited slip. The ICE vehicle is using electronics to control a mechanical system (the brakes and differential), while the EV should be able to do the same 100% electronically since it doesn't use the brakes to transfer power to a spinning wheel. So while I agree with you on what Kyle was doing, he shouldn't have to treat his Rivian like an ICE vehicle to get past those obstacles.

 

[White Shadow]

Looks like the quad motor set up will be THE best offroad setup that Rivian offers. Dual motor will not match it, according to this:

https://stories.rivian.com/difference-between-r1-drive-systems

 

[White Shadow]

I did read about the crawler gearing they're looking at offering. Frankly, it blew my mind. It has to be bolted on, and then the vehicle is not highway capable until you switch it back to stock gearing. How this is an improvement to the lever in traditional vehicles that can drop you to low range and back within seconds is quite beyond me.
?

https://www.thedrive.com/news/rivian-patents-bolt-on-low-range-crawler-gearbox-for-off-road-evs

Is this the link you've read? There are several articles on this patented gearbox, but it's not going to be something that you have to bolt on and then take off to drive on the road. It will be actuated, much like a transfer case is actuated in an ICE vehicle.

 

[White Shadow]

Boy oh boy did you upset the apple cart, RIP. What I read was a description of a specific problem inherent in the quad motor design.

What other people heard was an attack on their very souls. White shadow came out swinging like you had insulted his momma. If it was such a simple software solution, why haven't they implemented it? RIP has simply, succinctly, and accurately explained why a differential, without software, can be superior in low traction scenarios to a quad motor setup.

He has been on the same surfaces in his fully locked vehicle,and his quad motor, and talked about the results. Why oh why would anyone feel like they need to flame him or resort to personal attacks? Dude just made an observation.

White shadow, you must be real fun at parties. I mean, what did he do to you to get you so riled up?

LOL, what makes you think I'm riled up? Here's what you probably don't know---I own and drive a Jeep as a daily driver. I don't own a Rivian. I considered one, but ultimately decided against it at this point in time for various different reasons. That said, all of my comments here are based upon the absolute fact that having a motor independently power each wheel is the holy grail of offroad-ability. You simply cannot do any better. Not with lockers front, rear, and center. So my comments are all based upon the HOW and the WHY Rivian has chosen to make the R1T and R1S perform so poorly in CERTAIN offroad situations.

But I think I may have found my own answer----they are protecting the motors against overheating. It may not be as simple as that, but I think that's a big part of it. Case in point: Rivian's recent patent on low range gearboxes at each corner. While electric motors make excellent torque, it seems that too much heat is an issue and one way to get around that is by gearing.

And FWIW, next time try to attack the argument, not the person. You'll come off a lot better than you do making personal attacks.

 

[R.I.P.]

The wheel in the air is still getting turned, so some torque is being consumed to turn that wheel/hub/axle, etc... Wheels don't turn on a locked axle without torque being applied.

... 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.

 

[R.I.P.]

Looks like the quad motor set up will be THE best offroad setup that Rivian offers. Dual motor will not match it, according to this:

https://stories.rivian.com/difference-between-r1-drive-systems

That is too bad, and certainly disappointing.

 

[Zybane]

With a truly locked differential, you're splitting the available toque between two wheels. You'll never get it all to one wheel on a locked differential.

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?

 

[HaveBlue]

That is too bad, and certainly disappointing.

You know why they call it a story? That's what it is because if you put locking differentials in the dual motor it will run circles around the quad motor of road. Still won't be as good as an ice vehicle with 2 lockers though. Nothing beats all four wheels spinning exactly the same speed all the time from zero rpm on up. Electronics just can't seem to do that simple task. All you get is smoke either from the tires, the brakes or the motors.

 

[zipzag]

The reality is that the quad motor is designed to be a great Baja performer: High speed on a dry, loose and rough surface.

Unfortunently no one drives that way: The possibility of damage is high. And the involuntary manslaughter charge from killing a girl scout troop who happened to be on the trail is unpleasant.

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