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Quad motor vs locking diff

Dark-Fx

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To @Dark-Fx point, the dual motor will have a differential, and even with brakes holding the in air wheel, you won't get more than roughly 50% of the power from the axel to the planted wheel.

The clip starts where Mason, Rivians drivetrain VP attests to that fact.

I expect if there is room for some sort of a limited slip differential that there will be a company offering it as an upgrade.

Power is not the same thing as torque in this application though. The motor might be able to generate the same amount of power when only driving one wheel, but since the wheel has to spin twice as fast, you're losing half the mechanical advantage so the actual brake torque is halved. I'm not surprised this is a difficult concept to understand for some folks. It took me playing with an open differential at a children's science museum to actually finally grasp it.
 
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To @Dark-Fx point, the dual motor will have a differential, and even with brakes holding the in air wheel, you won't get more than roughly 50% of the power from the axel to the planted wheel.

The clip starts where Mason, Rivians drivetrain VP attests to that fact.

Yes, he does say that. I suppose possibilities include reducing the torque from the motor by half whenever traction control is engaged to protect driveline components, or maybe he is just reiterating common misconceptions about how a differential works. I don't know. It would not surprise me if they are dropping motor torque when traction control is engaged. It can put a lot of stress on components, and I have seen twisted brake plates off of trucks where the systems were abused.
 
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I expect if there is room for some sort of a limited slip differential that there will be a company offering it as an upgrade.
I had an F-150 for a while with brake based limited slip. I admit to s*** talking it a lot, being an off-road snob that prefers my ECTEDs and lockers. However, and it pains me to say this, I really do have to admit that it worked really well with things like snow and ice. Being that my Rivian really is not a rock crawler, and what I am most concerned about is slippery surfaces like snow and ice, I am coming around to thinking that I will likely be perfectly happy with Rivian's brake based traction control if it works as well as Ford's did.
 

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I had an F-150 for a while with brake based limited slip. I admit to s*** talking it a lot, being an off-road snob that prefers my ECTEDs and lockers. However, and it pains me to say this, I really do have to admit that it worked really well with things like snow and ice. Being that my Rivian really is not a rock crawler, and what I am most concerned about is slippery surfaces like snow and ice, I am coming around to thinking that I will likely be perfectly happy with Rivian's brake based traction control if it works as well as Ford's did.
Yes, brake-based eLSD does well on rocks, look at Toyota's ATRAC. Where it doesn't is in mud, sand, or snow where you need to maintain wheel speed. At least here in CO that's where many suggest a proper locked diff is better. Another place that locking my diff actually helped over ATRAC was on a steep hill covered in gravel/scree and ATRAC wasn't able to move power around quickly enough. Kick on the locker and the rig went right up with little fuss.
 

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Errm.. even if you can use a diff on the dual motor to send 50% of power to one wheel, that's still the equivalent of the 25% in the quad because you also have half as many motors? I honestly haven't paid attention to the dual motor specs - are the motors in there each equivalent to 2 quad motors? If not, then it's still less torque on the dual than the quad, so if torque to get over obstacles is an issue, I'm not seeing how dual motor solves that.

Apologies if I've misunderstood something or am unaware of some spec I should be aware of wrt the dual motor.
 
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Errm.. even if you can use a diff on the dual motor to send 50% of power to one wheel, that's still the equivalent of the 25% in the quad because you also have half as many motors? I honestly haven't paid attention to the dual motor specs - are the motors in there each equivalent to 2 quad motors? If not, then it's still less torque on the dual than the quad, so if torque to get over obstacles is an issue, I'm not seeing how dual motor solves that.

Apologies if I've misunderstood something or am unaware of some spec I should be aware of wrt the dual motor.
I think I understand it the same as you do. I would have scoffed at the idea that my ICE-powered Jeep could provide more torque to the wheels than the powerful Rivian electric motors, but the math seems to be lining up that way.
🫤
 

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Errm.. even if you can use a diff on the dual motor to send 50% of power to one wheel, that's still the equivalent of the 25% in the quad because you also have half as many motors? I honestly haven't paid attention to the dual motor specs - are the motors in there each equivalent to 2 quad motors? If not, then it's still less torque on the dual than the quad, so if torque to get over obstacles is an issue, I'm not seeing how dual motor solves that.

Apologies if I've misunderstood something or am unaware of some spec I should be aware of wrt the dual motor.
It removes the "wheel needs to slip to determine traction" issue, but further limits the drivetrains single wheel power vs the quad.
 

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This R.I.P guy doesn't really understand anything about how all of this works despite his careful thought experiements. His idea that a dual motor will be better on slippery roads is a red flag that he's clueless about motor software, sensors, and traction control systems. Here's a relevant video:

The Holy Grail Of AWD Systems | Rivian R1T - YouTube
 
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This R.I.P guy doesn't really understand anything about how all of this works despite his careful thought experiements. His idea that a dual motor will be better on slippery roads is a red flag that he's clueless about motor software, sensors, and traction control systems. Here's a relevant video:

The Holy Grail Of AWD Systems | Rivian R1T - YouTube
Cute link.

I am driving one on ice and snow, are you? Yesterday I took my old F-250 up the mountain, because the Rivian just flat goes sideways under certain conditions and as a death trap.

I know that people say it is snarky to say things like this, but if you are anywhere near the Pacific northwest, I invite you over to show me what I am doing wrong. Websites and links and people talking about how things are supposed to work are great, but when all those theories don't hold up on the ground they're not worth the time you took to watch them.

I can only assume you have not gone through this thread carefully, and absorbed the hundreds of hours of testing that have gone into trying to figure out why this vehicle is behaving the way it is on slippery surfaces. If you care to and have something constructive to add, you are welcome. If, on the other hand, you are just about trolling, then we can just note that and move on.
 

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Translation: "I have opinions and informed people like engineers or vehicle control specialists cannot change my mind because I have an offroad pit I go to and live in the PNW."

Your screed on why lockers are a must got how the quad motor system works entirely wrong. So why should we trust your non-specialist opinion? For instance you ignore that each wheel is looking at its traction situations thousand of times/second and adjusting as needed. You also ignore the elephant in the room which is traction - which is highly influenced by tires. The compound in the Pirelli Scorpions is an ELECT based compound which looks to balance rolling resistance with mechanical grip. It's not great on slippery rocks or mud. You want more traction? Get a different tire. The Rivian goes sideways in certain conditions going up a mountain? What are you talking about? A 2WD F250 can in no way approach the torque vectoring and traction control system of a well designed EV, and the traction issues inherent in traditional pickups are well known. Literally no one else has made the claims you're making, including those who live in far snowier and icier climates. Look at the video where Out of Spec tests a Defender vs the R1T. It's not even close.

Another thing here to note is that Rivian has consistently improved the off-road and on-road control software month-to-month. It's a different and better beast off-road and on-road than it was 12 months ago.
 
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Translation: "I have opinions and informed people like engineers or vehicle control specialists cannot change my mind because I have an offroad pit I go to and live in the PNW."

Your screed on why lockers are a must got how the quad motor system works entirely wrong. So why should we trust your non-specialist opinion? For instance you ignore that each wheel is looking at its traction situations thousand of times/second and adjusting as needed. You also ignore the elephant in the room which is traction - which is highly influenced by tires. The compound in the Pirelli Scorpions is an ELECT based compound which looks to balance rolling resistance with mechanical grip. It's not great on slippery rocks or mud. You want more traction? Get a different tire. The Rivian goes sideways in certain conditions going up a mountain? What are you talking about? A 2WD F250 can in no way approach the torque vectoring and traction control system of a well designed EV, and the traction issues inherent in traditional pickups are well known. Literally no one else has made the claims you're making, including those who live in far snowier and icier climates. Look at the video where Out of Spec tests a Defender vs the R1T. It's not even close.
...aaaand question answered, thank you. OMG, and your tire suggestion... THANK YOU! How could we have missed something so simple!

OMG, you are such a lifesaver I cannot thank you enough for getting us all straightened out on this.
🤦
 

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Just the fact that you said, "cute video" in relation to Jason Fenske's careful explanation of how the quad motor system works (and its benefits and potential) is a reason to not take you seriously. You don't even understand how/why Rivians "feel" the surface and spin tires in the air in a controlled manner when they are free/off a surface and that their spinning is not a reason for criticism given the fundamental differences in how it all works.. All I see here is an old man shaking his fist at the modern world and ignoring realities and change right in front of him in favor of edge cases and misunderstanding.
 

zefram47

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Just the fact that you said, "cute video" in relation to Jason Fenske's careful explanation of how the quad motor system works (and its benefits and potential) is a reason to not take you seriously. You don't even understand how/why Rivians "feel" the surface and spin tires in the air in a controlled manner when they are free/off a surface and that their spinning is not a reason for criticism given the fundamental differences in how it all works.. All I see here is an old man shaking his fist at the modern world and ignoring realities and change right in front of him in favor of edge cases and misunderstanding.
And all your loud ranting is proving is you haven't actually read a damn thing in this thread. Theoretical operation is great, but when the rubber meets the road, ice, trail, etc...theory goes out the window. In certain situations Rivian's system is absolutely not properly calibrated. As many have already said in the thread, depending on the hardware they've actually used it may be possible to get a lot closer to theory...but if they haven't, then it may never get better. On-road performance does not equal off-road performance and no vehicle will excel at both. Rivian has attempted to make a jack-of-all-trades and it shows and does many things well...but they are a master of none of these realms.
 

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It seems to me if some of their shortcomings can be mitigated, switched reluctance motors are better suited for this kind of application (i.e. four motor off/on road vehicle).

Though I suppose four ac type motors with a coil driver setup maybe workable as well. ue-graph-curve-for-EV-motor-controller-coil-driver.jpg
link


Nonetheless it will be interesting to see if Rivian’s in house motor design will improve things when/if they're implemented in the four motor variants.
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