Speaking of diffs

[R.I.P.]

There may be a perception that I was bashing Rivian when talking about the challenges posed when trying to off-road QMs, but that is not the case. In addition to the spooled Yodas having the same issues, so does that Hummer EV (in the rear) and I am confidant that the Tri-motor Cybertruck will suffer in those areas as well; there is just no way around it. Over on the CT forums there is faith that Tesla's "superior engineering" will be able to overcome the differential delete, but I am betting against that.

Of note, of all the E-trucks we have tested, the Lightning has the best traction characteristics. With excellent traction control and a real, physical locker in the back, it is, as of right now, the best handling truck in the super slick stuff. Of course the truck itself is not an off-roader, so actual obstacles stop it fairly quickly.

With Enduro lockers coming, that will give us every advantage the Ford has, in a more capable package.

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[SeaGeo]

How're you planning on adding lockers to the DM?

 

[HaveBlue]

It'll likely be an Eaton unit if they can squeeze one in there. Otherwise we'll have to make due with a lunchbox like a Powertrax; which tends to be noisy.

I helped ARB with some of their applications in engineering and would love that option since an ARB compressor is already on the truck but I don't think it's going to happen because there's no conventional carrier housing. It might be possible to route the air line out the side but the casing really doesn't lend itself to fitting all the right parts in all the right places.

 

[R.I.P.]

How're you planning on adding lockers to the DM?

There are two aftermarket outfits that are working up prototypes now. One of them is already in field testing, and I have volunteered my brand new DM for beta testing the unit.

 

[R.I.P.]

It'll likely be an Eaton unit if they can squeeze one in there. Otherwise we'll have to make due with a lunchbox like a Powertrax; which tends to be noisy.

I helped ARB with some of their applications in engineering and would love that option since an ARB compressor is already on the truck but I don't think it's going to happen because there's no conventional carrier housing. It might be possible to route the air line out the side but the casing really doesn't lend itself to fitting all the right parts in all the right places.

I'm running an Eaton in the rear, and an Auburn in the front of my TJ. I would be thrilled with either unit in my R1. Personally, I don't think that the powerrtax unit is all that much of an improvement over the already good traction control that the DM has. Brake heat and wear is one argument, but frankly I've never had any problems with that. Even under extended deep snow runs where the traction control was very active.

The prototype being developed is essentially an Eaton copy.

All that said, I really am going to be surprised if Rivian doesn't offer their own within 12 to 18 months.

 

[PBRAZ]

For my own education... Each motor on the quad has an electronic connect / disconnect (dog clutch). If both sides of the front and/or rear were engaged this would essentially be a locker, no? Right now it's a software decision not to have this capability. Or perhaps the dog clutch was not engineered to withstand that sort of torque?

 

[SoCal Rob]

For my own education... Each motor on the quad has an electronic connect / disconnect (dog clutch). If both sides of the front and/or rear were engaged this would essentially be a locker, no? Right now it's a software decision not to have this capability. Or perhaps the dog clutch was not engineered to withstand that sort of torque?

Only the rear motors have disconnects on the quad.

 

[PBRAZ]

Only the rear motors have disconnects on the quad.

Got it, thanks. Could be used as a locker, no?

 

[OrthoBlock]

For my own education... Each motor on the quad has an electronic connect / disconnect (dog clutch). If both sides of the front and/or rear were engaged this would essentially be a locker, no? Right now it's a software decision not to have this capability. Or perhaps the dog clutch was not engineered to withstand that sort of torque?

I believe this is not the case. The disconnects do not connect the axels across from each other in any way. They simply connect each respective motor assembly (rear only as noted) to the axle it drives.

 

[PBRAZ]

I believe this is not the case. The disconnects do not connect the axels across from each other in any way. They simply connect each respective motor assembly (rear only as noted) to the axle it drives.

Right. I suppose irregardless of the disconnects, why can't the drive system just tell both rear and/or both front motors to spin at the same speed? With 4 independent motors the quads should be the most capable off road production vehicles ever made. From this thread it sounds like those that offroad their vehicles often are not seeing that.

Perhaps Rivian hasn't gotten there yet with the software, and/or there are engineering limitations with some of the hardware components. But technically it seems a virtual locker is possible.

 

[OrthoBlock]

Right. I suppose irregardless of the disconnects, why can't the drive system just tell both rear and/or both front motors to spin at the same speed? With 4 independent motors the quads should be the most capable off road production vehicles ever made. From this thread it sounds like those that offroad their vehicles often are not seeing that.

Perhaps Rivian hasn't gotten there yet with the software, and/or there are engineering limitations with some of the hardware components. But technically it seems a virtual locker is possible.

While it's unlikely that anyone outside Rivian knows the answer to this 100%, my personal belief is that it is a limitation of the available torque at individual tire(s). There simply is not enough torque available (either because of limits of the motors/batteries, or through some software design that tries to protect systems, etc.) to spin one or more of the tires in specific situations.

While this may seem odd, given the gazillion pound-feet of torque that is stated for the vehicle, the issue stems from the limited gearing that is in place.

The mechanical solutions that have been suggested (either lockers, or low-range transfer case type extra gearing) both accomplish the same functional outcome with respect to the non-spinning tire: they provide more torque, so that the said tire can spin.

 

[R.I.P.]

For my own education... Each motor on the quad has an electronic connect / disconnect (dog clutch). If both sides of the front and/or rear were engaged this would essentially be a locker, no? Right now it's a software decision not to have this capability. Or perhaps the dog clutch was not engineered to withstand that sort of torque?

No. To be locked, there must be a physical connection between the wheels. A brilliant device was invented to do this in a way that automatically vectors torque to give the vehicle inherent stability in low traction situations, and a solid connection between the two when needed. It is called a differential. If there is no connection, like in the QM, there can not be any "locking".

The QM tries to simulate locking buy guessing with a computer. It does a poor job. To be fair, so does the Hummer EV, which is a pity as well, because otherwise it would be a monster.

 

[PBRAZ]

While this may seem odd, given the gazillion pound-feet of torque that is stated for the vehicle, the issue stems from the limited gearing that is in place.

That is the head scratcher right there. This drivetrain rockets a 7,000+ lb vehicle to 60 mph in 3 seconds. It seems like the motors and gearing are capable of getting the job done. We even have conseve mode where 2 motors still provide a pretty good punch.

I suppose off roading presents a different set of stresses on the various components. I'm sure the engineers tried a virtual locker and the results weren't to their liking.

 

[R.I.P.]

Right. I suppose irregardless of the disconnects, why can't the drive system just tell both rear and/or both front motors to spin at the same speed? With 4 independent motors the quads should be the most capable off road production vehicles ever made. From this thread it sounds like those that offroad their vehicles often are not seeing that.

Perhaps Rivian hasn't gotten there yet with the software, and/or there are engineering limitations with some of the hardware components. But technically it seems a virtual locker is possible.

Watch this:



It is a decent depiction of what happens when theory comes up against physics. Keep in mind, that is _not_ much of obstacle, and the truck that "beats" it is a pretty lame off-roader. In our experience it does not take much of an obstacle to get the QM in over it's capabilities. Here is the kicker; the DM crawls right over and through obstacles like that. Why? It's motors never stop and stall like the QM's do, why? It has differentials.

Rapters, TRX, Rovers, Jeeps, Broncos, name a capable off-roader, every one of them has differentials in them. This is no accident.

When we started talking to Rivian about our findings in February, one of the things we were told is that a DM would be coming, with differentials to address the problem. Yea Rivian!

They know.

Again, the people that love their QMs are going to howle, because they get they get their feelings hurt. So for the 100th time, I am not saying there is not place for the QM. In situations where traction is decent and there are at least 3 wheels on the ground, they perform well. Get two wheels off the ground or put them on very slippery surfaces and they suffer.

 

[OrthoBlock]

While no one asked, I personally do believe that the Quad Motor solutions have the potential to be superios to lockers in all* circumstances.

However, in it's current implementation the solutions falls short on performance relative to classic locker [and even advanced traction control] solutions that are out there.

In my mind, a quad motor with sufficiently powerful motors and/or gearing (basically getting to the same place) will allow for software based implementation that will beat out lockers and other brake based traction control devices in all* cases.

*[one should be careful when speaking in absolutes, as they are seldom correct: I'm guessing there is some scenario in which lockers, or other traction control systems, would still be better than the ideal quad motor solutions, even if I can not think of them at the moment.]

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