Rivian's plan for Rock Crawling is a low-range crawler gearbox. Is it something Cybertruck S.B. looking at?

[Aces-Truck]

I just saw this about a way to make Rock Crawling with an EV easier. Ideas on if it could be adapted to CT?

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

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[Sirfun]

Personally it wouldn't bother me one bit if my Cybertruck was geared in a way to where it would have more grunt and a top end of maybe 110mph. (think about off road tires speed rating).
4 gearboxes. One at each corner, doesn't seem like an easy way to rock crawl.

 

[Ogre]

Rivian patents thing which they never deliver on. Remember the “Tank Turn”?

It’s a PR patent. Released to get media with almost zero chance it’ll be applied in the real world.

 

[Crissa]

That's no different than Tesla's defensive patents. You do this thing because it's a method, not because it turns out it's easy.

-Crissa

 

[Zabhawkin]

Pretty sure I have seen it before... oh yeah its on the original on many military vehicles. look up portal axles. There are several aftermarket kits available as well.

 

[slomo]

Electric pickups are inferior to ICE vehicles in both rock crawling and difficult slippery conditions. Rivian owners who have experience with full locker ICE vehicles know this. CT owners with siilar experience will learn this.

Lockers on the two motor CT would make a big improvement over rivian. Odds are the two motor CT doesn't have lockers. Four motors is not the same as lockers. Rivian can't lift itself from a stalled position on a single quad motor. That's why the patent above was filed. It's likely that CT is similar.

 

[JBee]

This is one of the reasons I posted a thread a while ago that CT (as is now confirmed for semi too) will have smaller type QM Plaid motors. The faster rpm allows them to operate at higher gear ratios for off road and still sit in the efficiency rpm band for cruise.

 

[FutureBoy]

I’m no expert here so excuse what may be a stupid question.

Is there something the extra gearing (resulting in extra parts, failure points, maintenance) would provide that cannot be done in software?

From what I understand, torque is plenty abundant. Tire grip wouldn’t be changing. The lower gears don’t affect the coordination of tire spin. So really, I’m seeing this as a precision control issue. How easy is it to calibrate, using a foot petal, the exact amount of tire rotation and speed to each specific obstacle.

Assuming that is the case, couldn’t the solution be to change the rate of power application accepted through the foot pedal? So instead of variable steering (I want that too though) have variable power pedal action. So in off road mode, a full pedal push could provide max torque but only allow a max speed of say 20 mph.

Easier to change the software than the hardware.

 

[slomo]

This is one of the reasons I posted a thread a while ago that CT (as is now confirmed for semi too) will have smaller type QM Plaid motors. The faster rpm allows them to operate at higher gear ratios for off road and still sit in the efficiency rpm band for cruise.

Cool. Tesla's in-motor traction control may be superior to Rivian and others too.

 

[Crissa]

When comparing a mature technology you're familiar with vs a new technology you're not familiar with...

Perhaps that's not a great time to state one is 'superior' to the other.

Just sayin'.

Locking axles are not unique to ICE vehicles, nor are they the best at rock crawling. The best rock crawlers are these:

-Crissa

 

[Zabhawkin]

I’m no expert here so excuse what may be a stupid question.

Is there something the extra gearing (resulting in extra parts, failure points, maintenance) would provide that cannot be done in software?

From what I understand, torque is plenty abundant. Tire grip wouldn’t be changing. The lower gears don’t affect the coordination of tire spin. So really, I’m seeing this as a precision control issue. How easy is it to calibrate, using a foot petal, the exact amount of tire rotation and speed to each specific obstacle.

Assuming that is the case, couldn’t the solution be to change the rate of power application accepted through the foot pedal? So instead of variable steering (I want that too though) have variable power pedal action. So in off road mode, a full pedal push could provide max torque but only allow a max speed of say 20 mph.

Easier to change the software than the hardware.

It would be hard to say for certain but gearing gives a significant amount of low speed control. Can that be duplicated in software by remapping the throttle response? Probably, time will tell.

The example Crissa posted has a combination of a very flexible suspension and insane gearing as well as only one purpose. Road going vehicles even like my Ugly still have to be able to be driven on regular roads at reasonable speeds which requires compromises.

Edit to add: Many rock crawlers like the idea of electrics due to max torque at very low RPM.

 

[slomo]

The problem with Rivian so far is getting stuck a zero RPM on an uphill with only one or two wheels having traction. It's unclear if the motor controller is limiting power for thermal or safety reasons. Or if the motor simply can't generate enough torque at near 0 RPM to move the vehicle.

With enough traction the low speed power and control is impressive. But the ratio or vehicle weight to tire size is not good on the Rivian. The tires don't air down well due to needing stiff sidewalls for a 7K pound vehicle.

MRAP/Unimog grade tires do air down well. Diesel pickups tire, similar weight to CT, do not typically air down well. So I don't assume that the reasonably priced tires Tesla will use on CT will be great offroad.

Hopefully the CT is at least in the weight range of the Lightning. A 10K GVWR seems about right.

 

[JBee]

I’m no expert here so excuse what may be a stupid question.

Is there something the extra gearing (resulting in extra parts, failure points, maintenance) would provide that cannot be done in software?

From what I understand, torque is plenty abundant. Tire grip wouldn’t be changing. The lower gears don’t affect the coordination of tire spin. So really, I’m seeing this as a precision control issue. How easy is it to calibrate, using a foot petal, the exact amount of tire rotation and speed to each specific obstacle.

Assuming that is the case, couldn’t the solution be to change the rate of power application accepted through the foot pedal? So instead of variable steering (I want that too though) have variable power pedal action. So in off road mode, a full pedal push could provide max torque but only allow a max speed of say 20 mph.

Easier to change the software than the hardware.

I'm 100% sure the CT will remap throttle inputs to suite terrain, like snow mode on Tesla reduce power output according to traction. That's not actually the issue though.

Heat is the performance limitation in all electric motors. All electric motors have an efficiency heat map:

Now if you look at the map, consider that the inefficiency is energy being converted into heat energy and not kinetic energy for forward motion. That means this motor above, at high torque levels and low rpm is converting half (50%) of the energy into heat. Let's say each motor on a wheel is producing 10kW of torque in a off road situation, that means its also producing 40kW of heat! (Or 20 room heaters!)

Now even if you can get the heat out of the stator with a cooling loop to a radiator the rotor can't really be plumbed up because it spins. So the motor heats up really fast, that means failing windings, de-magnetisation (in PM motors), tolerance changes from thermal expansion that also lead to bearing failure etc. It's a problem that is normally addressed by having a gear ratio which puts the electric motor at a higher RPM.

Whilst rock climbing, or travelling slow in hard terrain, your wheel might only be doing 60 rpm, which depending on your gear ratio means the motor is only doing a few hundred rpm, but at high torque, which is very low rpm on that heat map.

But if you have a higher gear ratio, you also end up spinning the motor faster than you need to at highway speeds, where less torque is required, pushing you on the other side of the map, and down low towards the blue area again, and can cause you to end up running out of rpm for top speed. This is where the Plaid motor excels in that the CF wrap allows for a closer rotor to stator air gap, as it prevents the rotor from expanding from centripetal forces at high rpm. The closer gap means better efficiency throughout the rpm range, (imagine an expanded center region of that heat map) without having to limit top rpm as much because of rotational expansion of the rotor. (Plaid goes up to 23,000rpm btw)

This means higher overall ratios can be used with the CF wrap motor that in turn pushes it into the higher RPM and better efficiency band of the motor. Because of this, you can also put more power through a smaller faster spinning motor for short periods of time, which is where Teslas get their strong acceleration performance from until they start overheating. Which is why they had to upgrade the Plaid cooling as well, because around the track it would overheat and debate performance to protect itself.

Essentially, the better efficiency you can operate the motors at, the less heat that needs to be managed, and the more performance you can get out of a motor. So if a two speed gearbox helps you do that, or a CF wrap, you choose which works best for your intended application.

 

[FutureBoy]

I hear what you are saying... Not sure I am interpreting your graph the same way you are though.

I'm seeing 2 options in this graph if you don't want to over-heat the motor. You can let it spin as fast as you like (well until the rotational forces explode the motor). If you are driving at any speed but the with very little torque no problem. So the less mass of the vehicle, contents, trailers, toys, etc the better. And try to reduce wind resistance as much as possible. Cool. Tesla basically rules that game.

But the second option in that graph looks like you can max out the torque all you want as long as you keep the rotation speed low enough. So if you gear up to say 1 motor rotation = 5 tire rotations, then as long as the max torque is strong enough, you could potentially run those motors as long as you wanted so long as you keep the rotation speed of the motor below say 500 rpm.

Now I know that the gearing I made up here is completely bogus. I rode long distance bicycle rides a lot growing up and the difference between starting in 1st gear vs 12th gear is insane. But theoretically we are now at a gearing problem. Looking at the Tesla M3 specs, the gearing is set at 9:1. With my limited knowledge and a bit of guessing, I assume that means 9 motor rotations for each tire rotation. I haven't found what the gearing ratio is on the Rivian. But looking in the article that started this whole thread, it says:

The patent states the reduction could be between 1.5:1 and 5.0:1.

? Workin' 9 to 5...? - Sorry, got distracted there.

Anyway, so Rivian is thinking that they could add some gears and improve the system. It looks to me like they are trying to move the gearing so that the high torque of rock climbing is happening further to the left (lower rpms). Given the heavy weight of the Rivian, the amount of torque needed to do cool rock climbing etc would be very high. So it makes sense. But there needs to be a balance because you need to be able to turn the wheels at a high enough speed to keep your momentum up in some areas. And I hope that the patented gearing allows for the driver to turn off the low gearing when desired so that they can drive home after having fun out in the wilds.

From what I've seen of Rivians out rock climbing, there are often times when the driver is trying to ascend an obstacle and will just mash the throttle to the ground. At the start this helps build up momentum. Then as they climb, the tires start to slip and lose traction so traction control kicks in and keeps the tires from losing grip. I'm not sure how their traction control works but if it involves using the brakes to slow the spin then that would potentially increase the need for torque and push the curve further into the over-heat zone.

So my thoughts for the CT are that if you limit the max throttle, you can potentially help mitigate the situation by lowering the fight between the throttle and the brakes in this situation.

But as you can see, I'm no expert here. I just trust that Tesla will have thought of this rock climbing issue. How it will prioritize in the delicate balance of features and trade-offs I don't know. I look forward to finding out though.

 

[JBee]

I hear what you are saying... Not sure I am interpreting your graph the same way you are though.

Sorry I think I didn't explain exactly what a "efficiency heat map" is. The colouring scale on the graph is not heat output, rather motor efficiency. That means the red areas make less heat than the blue areas. So you want to optimise to run in the red areas to keep the motor cool.

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