Lockers on Dual Motor, like the Lightning?

[SurfnBike]

Will the Dual Motor variant have mechanical lockers like the Ford Lightning (rear locker only)? I am a long time off-roader and I am so far unimpressed with the footage I've seen of the R1T quad motor in situations where one wheel has zero or near zero traction.

On a side note, I also wonder why they can't just add a software mode "lockers" that will spin both left and right motors front/rear at identical speeds. I'm not an engineer, just a software guy, so please excuse me if that's technically infeasible.

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[SeaGeo]

No. Word from Rivian is that it does not appear to have a mechanical locker.

 

[SurfnBike]

Well that is disappointing. My '05 Tacoma had a rear locker and so does my current F150. Never been a fan of using computerized braking to get traction; that's not for real offroad use but more of an emergency situation, e.g. running into a small patch gravel or snow here and there.

 

[White Shadow]

Well that is disappointing. My '05 Tacoma had a rear locker and so does my current F150. Never been a fan of using computerized braking to get traction; that's not for real offroad use but more of an emergency situation, e.g. running into a small patch gravel or snow here and there.

They should at least put an electronic limited slip differential on it. That's about as close as you can get to a locker without actually installing a locker.

 

[the long way downunder]

RJ said their dual motor doesn't have diff locks. So traction control will be the primitive brake system … the motors put out power and the brakes resist the power … which is why the quad motor is far superior. Diff locks break axles in the extreme, especially with a lot of torque and a lot of weight.

Rivian also wrote in one of these recent emails that there will be a quad motor max pack in the future.

I think Rivian really needs to work on their communications, not just their products and engineering.

 

[dleepnw]

There was an interview done with a Rivian engineer months ago, i can't recall who interviewed them (might have been Rivian Stories) but there is no mechanical locker on the dual motor. from the way it was described it could be an atrac type of system.

 

[White Shadow]

RJ said their dual motor doesn't have diff locks. So traction control will be the primitive brake system … the motors put out power and the brakes resist the power … which is why the quad motor is far superior. Diff locks break axles in the extreme, especially with a lot of torque and a lot of weight.

Rivian also wrote in one of these recent emails that there will be a quad motor max pack in the future.

I think Rivian really needs to work on their communications, not just their products and engineering.

But the quad motor will basically do the same thing....it's similar to a traction/brake-based system where on a traditional modern 4x4, the spinning wheel receives brake pressure so that torque is transferred to the other wheel on the same axle. But in the case of a quad motor EV, they can simply apply more torque to the wheel that isn't slipping. Same concept, slightly different approach to getting there.

I argued in another thread that it would be easy to simulate lockers on a quad motor Rivian and I still think that's true. But some people pointed out that you may not always want straight up locker type action and that's a valid point. It completely depends upon the terrain and the situation. That's why I suggested that an electronic limited slip differential might be the way to go. That's what some of the best 4wd vehicles use today in place of lockers and it works really well.

 

[derekmw]

Yeah, buckle in, this thread is going to end up 15 pages long with arguments from both sides.

 

[mmiles2012]

Well that is disappointing. My '05 Tacoma had a rear locker and so does my current F150. Never been a fan of using computerized braking to get traction; that's not for real offroad use but more of an emergency situation, e.g. running into a small patch gravel or snow here and there.

Watch Doug DeMuro's off-roading video - he raises a very interesting point in that the WAY you drive a quad motor off-roader is fundamentally different regarding this. When a wheel slips, they've designed the system to sense that and respond by "seeking" a wheel where torque applied = forward motion (you'll see some videos where the wheels appear to hunt for traction like this). And the actual, Rivian design team recommended, approach to this in limited traction scenarios is to apply MORE throttle/go pedal (in a true "do-what-I-mean" design sense - I want the car to go forward more, so I press on the throttle more).

It's different. Not going to say better or worse as I'm not an expert. But from an engineering standpoint it should actually work better because I can apply maximum torque to the wheel where it will most benefit the forward progress of the truck over the obstacle. Without having to worry about drivetrain losses/compromises from different modes of "differentials" between motor and wheel.

 

[the long way downunder]

But the quad motor will basically do the same thing....it's similar to a traction/brake-based system where on a traditional modern 4x4, the spinning wheel receives brake pressure so that torque is transferred to the other wheel on the same axle. But in the case of a quad motor EV, they can simply apply more torque to the wheel that isn't slipping. Same concept, slightly different approach to getting there.

I argued in another thread that it would be easy to simulate lockers on a quad motor Rivian and I still think that's true. But some people pointed out that you may not always want straight up locker type action and that's a valid point. It completely depends upon the terrain and the situation. That's why I suggested that an electronic limited slip differential might be the way to go. That's what some of the best 4wd vehicles use today in place of lockers and it works really well.

The quad motor can change its torque output much faster than ABS can cycle to absorb power.
The energy absorbed by the brake is the differential of the power going to ground across that axle … it's not a trivial waste. With sustained operation, the brakes heat up.
The quad can simulate three diff locks, rotating all four wheels in synchronous, or it can be smarter than diff locks, that can bog a vehicle down in mud or snow, and instead turn each wheel at the speed interpolated from the behavior of all four wheels, the steering angle, vehicle inclination and lean angle, suspension compression and load sensing.
Meanwhile, ABS just go "brrrr" … : )
If/when Rivian writes the code, the quad will go where the dual quits.
I can only hope the dual gets the same suspension. I'm concerned that they might have dumbed down the suspension to save on costs and to house the dual motors in a cheaper assembly or make space for more battery, etc.

 

[the long way downunder]

Watch Doug DeMuro's off-roading video - he raises a very interesting point in that the WAY you drive a quad motor off-roader is fundamentally different regarding this. When a wheel slips, they've designed the system to sense that and respond by "seeking" a wheel where torque applied = forward motion (you'll see some videos where the wheels appear to hunt for traction like this). And the actual, Rivian design team recommended, approach to this in limited traction scenarios is to apply MORE throttle/go pedal (in a true "do-what-I-mean" design sense - I want the car to go forward more, so I press on the throttle more).

It's different. Not going to say better or worse as I'm not an expert. But from an engineering standpoint it should actually work better because I can apply maximum torque to the wheel where it will most benefit the forward progress of the truck over the obstacle. Without having to worry about drivetrain losses/compromises from different modes of "differentials" between motor and wheel.

This vid?

Doug wasn't showing any apparent skill or prowess. He's owned a lot of expensive and "best" off-road vehicles, but he seemed to be wanting to put the R1T crossed up and compel it to figure out the traction, which is fine, it would give up no information to pick a clean line and roll up there at a steady pace with just enough momentum to let the suspension do the work.

He was in an early press beater with original software that was frankly crapola, and I'm no fan of those factory tires. If we're talking about the same particular track, he took a particularly difficult route and didn't try to improve his line, but eventually clambered up with no real drama. Someone came along in an upgraded off-road vehicle and failed to make it up the same track, or just didn't even try.

I'm sure he'd do a lot better today with K02s at 30psi and the latest rock crawl mode. He I think correctly describes what was true then and no much improved today, though I think the suspension is now a tad softer and more compliant. There's still bizarre behavior in the software. They've decided you need to use disproportionate throttle movement to receive anywhere near max torque for traction. It's a rubbish design at present. Snow mode seems to be less crippled than Rock mode.

I'd like to see the touchscreen with an off-road mode that shows each corner with two bar graph indicators, one for requested power with actual power, one for computed traction. There should also be all the usual indicators (lean angle, front-rear pitch, steering angle, suspension position, tire rotation.) Of course Rivian DNF'd on design of underbody cameras, spotter mode, lens washers, manual suspension height controls, extraction modes (e.g. max suspension lift, sand extraction constant rotation) and climb/descent speed control, etc.

Of course there's no winch, and the air suspension is very slow (though I read it's going to be faster with a bigger tank s00n.) Whatever they learned from 2018 thru 2021, they didn't implement. Mercedes suspension can hop, it's that fast. Land Rover has a great spotter mode in the cameras and transparent hood/bonnet mode. Everybody has camera washers. Hummer has underbody cameras. Everybody has HUD.

Rivian is first with quad motors – the ultimate solution – and 800hp and torque … but didn't bring any of the tech to match the capabilities of the motors, and hasn't written the software. We still don't have tank mode … Mercedes is going show up with their tank mode ("G turn") in 2025 … will Rivian deliver tank turn mode before Mercedes? : )

 

[White Shadow]

The quad motor can change its torque output much faster than ABS can cycle to absorb power.
The energy absorbed by the brake is the differential of the power going to ground across that axle … it's not a trivial waste. With sustained operation, the brakes heat up.
The quad can simulate three diff locks, rotating all four wheels in synchronous, or it can be smarter than diff locks, that can bog a vehicle down in mud or snow, and instead turn each wheel at the speed interpolated from the behavior of all four wheels, the steering angle, vehicle inclination and lean angle, suspension compression and load sensing.
Meanwhile, ABS just go "brrrr" … : )
If/when Rivian writes the code, the quad will go where the dual quits.
I can only hope the dual gets the same suspension. I'm concerned that they might have dumbed down the suspension to save on costs and to house the dual motors in a cheaper assembly or make space for more battery, etc.

I agree with you completely, but the issue is that the quad motor just doesn't operate that way. I still wonder why....and from what I've seen online, they have a long way to go before we see a quad motor Rivian compare to even something like a Subaru when it comes to putting torque to the wheels that can actually use it.

But on paper, nothing should be better than a properly set up quad motor vehicle. The real question is why didn't Rivian set it up to maximize traction in all scenarios.

 

[SurfnBike]

I'd trade all the tech for mechanical front and rear lockers. I've done a lot of offroading in my life and haven't found a better solution. It's also easier on the trail and your tires. That video looks like it's just a matter of time before multiple tires get shredded and abused on those rocks from the start/stop application of torque.

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