Quad motor vs locking diff

[R.I.P.]

You don't have to get wheel slip when you're measuring the motor position. If they're using a pure back-EMF design, they might have some trouble at exactly 0 speed, but advanced motor control ICs can measure the inductance at 0 speed as well to determine phase without encoders. With 12.6:1 reduction from the motor, you're entering a pretty decent measurable range as soon as you're moving at all, and again, you're not sensing wheel slip, you're sensing motor phase and controlling torque to keep the motor phases in 'sync'. (the phases are all independent, just would be locked to the relative positions when you turn on the 'locker mode').

With an unloaded wheel like in the first example, you would likely see about as much wheel movement from the speed sync control as you would see from the compliance of a 4WD axle system loading up.

The type of motor controller you reference is normally used in low speed electric motors. Is it doable in a vehicle designed for freeway speeds? Probably. I know Rivian's controller does not work like that now, because I am driving one.

Here is the other part to that. If I live in Denver, and I want to get to Kansas, there are a couple of ways to go. I can travel a short distance East, and I have achieved my goal. I can of course go West, and with a lot more work and expense get to Kansas by going around the world.

I fall in the camp that would judge the more elegant choice being just go East.

Rivian techs I have discussed this with tell me they are well aware of the quad-motor's limitations, but that is being addressed with the new dual motor variant. If, like me, you would rather have the benefit of a differential at each axle, they will be building a variant that we will be happier with. There, problem fixed. Can you throw a lot of resources into trying to make the quad behave more like the dual? Sure, but why would you? You just end up with a heavier, less efficient, more complicated system that that may or may not vector as well as a differential.

Lighter, simpler, more efficient, with traditional, predictable handling on slippery surfaces... yes please.

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[White Shadow]

Meanwhile, you're touting capabilities of a model that doesn't even exist yet. ? While what you claim could prove true, only those within Rivian know what its capabilities are.

Exactly this. My problem with him is that he's usually speaking in absolutes, telling us what is and isn't possible (and often wrong, BTW), but then tries to back up his opinion by challenging people to prove him wrong on a dirt hill in Oregon.

 

[R.I.P.]

Meanwhile, you're touting capabilities of a model that doesn't even exist yet. ? While what you claim could prove true, only those within Rivian know what its capabilities are.

Yes sir, I am hoping for the next version to perform better than the one I have. Am I missing why that is not appropriate...?
?

 

[MountainBikeDude]

@R.I.P. load up a factory optioned jeep gladiator without aftermarket alterations to 7000lbs, put similar tires on compared to the T, then run both through the same situations. Film it, and put it on youtube. This is the only way you'll be able to stand on your soapbox and not be questioned by people.

I also understand the outside uses you're outlining as highlighting the limiting factor within the system. Keep in mind, the Rivian isn't marketed as an extreme anything, more of a beyond capable jack of all trades both on and off road.

 

[R.I.P.]

Exactly this. My problem with him is that he's usually speaking in absolutes, telling us what is and isn't possible (and often wrong, BTW), but then tries to back up his opinion by challenging people to prove him wrong on a dirt hill in Oregon.

Well, yes, I am 'absolutely' disappointed with how the quad-motor design comes up short when pitted against my other, older tech. Frankly, it is not what I expected, and I am sharing my ownership experience with you.

Evidently this has caused you to have a "problem with me"? I apologize for offending, it was not the purpose of this post.

 

[the long way downunder]

Shortcomings of the quad motor are entirely software.
It would be great to have Max Koff explain what they're doing.
Once Rivian publishes a simple "3 diff lock" mode, quad will perform.
Quad can be more efficient than dual because diff locks absorb power.
Diff locks are slow. Quad motors are real time.
With correct software, quad can outperform any other configuration.
Rivian's software development is … behind.

 

[R.I.P.]

@R.I.P. load up a factory optioned jeep gladiator without aftermarket alterations to 7000lbs, put similar tires on compared to the T, then run both through the same situations. Film it, and put it on youtube. This is the only way you'll be able to stand on your soapbox and not be questioned by people.

I also understand the outside uses you're outlining as highlighting the limiting factor within the system. Keep in mind, the Rivian isn't marketed as an extreme anything, more of a beyond capable jack of all trades both on and off road.

Well, unlike Kyle I am not a yubtub guy lol. That is why I posted his vid. What I have experienced is on full display in his vid. Note how the vehicle "hangs" on the off camber test, with only two wheels spinning. Note the un-controlled spin of some wheels on the rock climb, causing dicey slides. It is all there, I just posted it for anybody that was interested, along with my similar experience.

As for being questioned, there ended up being a lot of people that don't even own one saying "nuhuh". Weird, and childish really. I drive one, have experienced the same things Kyle demonstrated in his video, and shared my experience. If somehow this offended people, I just don't know what to do with that.

 

[R.I.P.]

Shortcomings of the quad motor are entirely software.
It would be great to have Max Koff explain what they're doing.
Once Rivian publishes a simple "3 diff lock" mode, quad will perform.
Quad can be more efficient than dual because diff locks absorb power.
Diff locks are slow. Quad motors are real time.
With correct software, quad can outperform any other configuration.
Rivian's software development is … behind.

That would be great. But now you may get flamed for insinuating that Rivian is "behind" lol.

 

[dorsai]

A few points - Rivian's software right now is definitely behind where they want it to be and it's not living up to its potential right now. But I think it's potential is far higher than RIP does.

It reminds me a bit of the debates between mechanical LSD and brake based electronic LSDs, where the early implementations were subpar, but well tuned electric LSDs provided equal performance on the track.

Also, I'll bet that the dual motor Rivians won't have a locking diff, just brake based LSD with open diff like most Teslas except Plaid, though they could surprise, given the mechanical disconnects they included for the rear drive unit.

 

[R.I.P.]

I've already explained why a quad-motor Rivian will never be as good off-road compared to an off-road 4x4 with center, rear and front locking diffs in the off-road section.

Rivian quad motor acts more like a "good" AWD system. That is why it struggles even over some pretty small/basic obstacles.

Perfectly put, and completely accurate. Thank you.

 

[racekarl]

Here is the other part to that. If I live in Denver, and I want to get to Kansas, there are a couple of ways to go. I can travel a short distance West, and I have achieved my goal. I can of course go East, and with a lot more work and expense get to Kansas by going around the world.

Either something just whooshed over my head, or you are *really* bad at planning trips...

 

[R.I.P.]

Kyle's video doesn't apply to some of the claims you're making. What I got out of the video was this----the way the Rivian vehicles is currently set up isn't even as good offroad as a basic brake-based 4wd or AWD system.

Proof? Easy---when Kyle took his R1T and put it at the bottom of the hill in that off-camber situation, he had one front tire and one rear tire spinning. The other two tires weren't moving at all. Even a basic AWD or 4wd system will brake the spinning wheel to send at least some torque to the wheel that isn't spinning. That's the easiest and most simple way to move torque across an axle. But since Rivian doesn't have wheels connected by axles, they can EASILY fix this with nothing more than software. I'm just surprised that they didn't bake it into their vehicles in the first place. There's no reason whatsoever that we should see any Rivian sitting there spinning one front tire or one rear tire, while the opposite tire does nothing....at least not in any type of offroad driving mode.

LOL. You have oscillated from "you are all wrong, quad motors are better that a locking diff" to "they are not even as good as a brake based AWD"? I am having having trouble keeping up with ya man, you are switching sides too fast.

Hey, I admit 'tho, I am old & slow these days.

Yes, I agree. My R1T is _not_ as good on simple obstacles as an inexpensive brake-based AWD vehicle is. You say "they can easily fix this".

Well, that would be nice. Here is to hoping.

 

[White Shadow]

Well, yes, I am 'absolutely' disappointed with how the quad-motor design comes up short when pitted against my other, older tech. Frankly, it is not what I expected, and I am sharing my ownership experience with you.

Evidently this has caused you to have a "problem with me"? I apologize for offending, it was not the purpose of this post.

No, my problem with you is in the very first post of this thread. Your entire premise is incorrect and you don't want to back it up with facts other than to make some silly challenge for people to prove it to you in Oregon. Sorry, that's not the way a message forum works. You conveniently ignored my posts asking you to prove to me why it's not possible to make a quad motor vehicle that essentially outputs the same speed to all the wheels all the time. You said it's not possible, but it's entirely possible to do that. And that would be completely equivalent to a fully locked drivetrain on a conventional 4wd system with front, center, and rear locking diffs.

 

[Inkedsphynx]

After reading all this, I guess my thoughts are... Shrug?

Anecdotal only, but I've yet to have any situations my T couldn't handle. I've not managed to get my T sitting all 4 wheels on top of 4 big boulders to figure out if one of them is loose, but then again, in all my years of overlanding and offroading I don't think I've ever come across a real world situation where the correct line was to get my truck up on top of 4 boulders ?

I have had boulders slip out from under the tires on my T, and my Defender, and my Ram, and my F250... It happens to every vehicle.

I also don't tend to drive down loose off-camber slopes, in any vehicle. I can't think of a single time I've done any overlanding and that was the only option I had, so as with anything, I know my and my vehicles limitations and I avoid obstacles that are too risky for either.

I still believe the R1T is the most capable stock overlander I've ever owned. It performs better than my Defender in every situation I've run across with it, and western Washington is hardly Moab.

Nothing about my post is disputing or arguing any of the underlying technical points. I honestly haven't stuck my R1T on a slipper off-camber slope. I doubt I will. So far, at least, my T has taken me every single place I've wanted to go, regardless of the conditions. That's why I bought it. That's a win to me. If it can't get me to 2% of places.. I'll live with that.

To me it is like this: Would I rather have a kitted out Taco that can do the things the OP is saying the R1T can't, but drives like absolute garbage any time it's not sitting on top of 4 boulders, or would I rather have an R1T that drives like an amazing machine in every circumstance except those couple that the Taco would excel at?

As others have said, jack of all trades, master of none. If I want to do hardcore rock crwaling, I'll build/buy/drive a dedicated rock crawler. If I want to drive over the mountains, get off the beaten path, then rip it home at 100mph in luxury and comfort... What are my other options exactly? In the EV world, none

 

[zefram47]

It reminds me a bit of the debates between mechanical LSD and brake based electronic LSDs, where the early implementations were subpar, but well tuned electric LSDs provided equal performance on the track.

And eLSD programming even like Toyota's ATRAC still has limitations that mechanical lockers don't while off-road. Mechanical LSDs also come in several flavors that behave differently, clutch pack vs geared (Torsen) for instance.

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