Canthoney

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Why Rivian’s "Tank Turn" Stationary Spin Feature Is Delayed
Short answer: It’s a lot harder than it looks to do it right.

https://www.motortrend.com/news/why-rivian-tank-turn-stationary-spin-feature-is-delayed/

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“Back in 2019, Rivian lit up the automotive internet with Tank Turn, demonstrated by the 2022 Rivian R1T in a viral YouTube video. Since then, though, the company has announced the feature is delayed and won't be ready at launch. There are several reasons why, which R1T chief engineer Charles Sanderson walked us through.

Tank Turn takes advantage of the R1T pickup and the R1S SUV's quad-motor platform to make the vehicle to spin like a top; to do so, the motors and wheels on one side of the vehicle rotate forward and the wheels and motors on the other side rotate backward at the same time. It's a devilishly simple idea that's proven much harder to program than you'd expect, and the core concern is safety. Getting the truck to Tank Turn safely and consistently is not a small challenge.
The biggest issue is the number of variables involved. What you see in the video was a best-case scenario, and the Rivian team was lucky enough to capture a good turn on the first try.

First, unless conditions are perfect, it's possible each wheel will have a different amount of grip than the others and require more or less power to break traction. While the truck's computer can read the road surface via suspension inputs as you're driving, there's no good way for it to know exactly what the surface under each tire is like when you come to a stop. If any wheel is getting too much or too little power during a Tank Turn, it can cause the vehicle to spin off in a random direction instead of rotating in one place. Power delivery has to be programmed very carefully to respond to changing grip before and during a Tank Turn. You can see this issue crop up right at the beginning of the video.

Next, because the truck's wheelbase isn't square (that is, because there's more distance between the front and rear axles than there is between the wheels on either side of each axle), it won't always rotate around the exact center of the vehicle, especially if the surface isn't consistent. If the point of rotation is off center, it can cause the vehicle to spin off in any direction instead of rotating in one place. A safeguard needs to be programmed to recognize this situation and either correct it or end the Tank Turn.

Then there's the matter of gravity. In order to execute a Tank Turn, all four wheels have to break traction. Once that happens, the truck is at the mercy of physics. If the surface is inclined in any direction, the truck will slide that direction as it spins. A safeguard needs to be programmed that can recognize this and shut it down before the truck spins into a tree, a ditch, or worse.

Finally, there's the matter of speed. During testing, Rivian discovered the amount of power needed to get all four wheels spinning results in a lot of wheel speed, which ends up making the truck spin around very fast. From inside the truck, it's a hell of a ride, so much so there's concern it'll scare drivers who aren't ready for it, which could result in a loss of control if the driver panics. Speed, of course, also exacerbates all the above issues.

Put it all together, and Tank Turn is really only easy to do in the middle of a big, flat, slippery field. Making it work anywhere else is a big challenge. The places a Tank Turn would actually be useful off-road are never level, wide-open spaces. The amount of programming and testing needed to make Tank Turn work safely and predictably is far too great for Rivian to develop it purely as a gimmick, so the engineers are dedicated to making it actually useful.

Right now, though, the majority of Rivian's engineering resources are dedicated to getting the R1T, R1S, and Amazon van out the door as smoothly as possible. After that, they'll have the R2 and R3 models to work on. Although the team hasn't forgotten about Tank Turn, a complicated off-road tool that most buyers will only ever use once to show off to their friends and family just isn't a top priority. Sanderson couldn't give us an updated timeline, but he knows full well how cool Tank Turn is and how plenty of people on his team are eager to perfect it.”
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P.S.Mangelsdorf

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Canthoney

Canthoney

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Based on my reading of it and some other comments I’ve seen, I don’t know if this will ever be a feature. It sounds like something they can do, but it is also very risky if the conditions aren’t perfect. I’m personally OK if they don’t put the tank turn feature in, it’s a cool gimmick but obviously not very useful. I would be more interested to see if they could ever do rear wheel steering, or the crab walk like the GMC Hummer EVs or if they would require additional hardware
 

Autolycus

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Based on my reading of it and some other comments I’ve seen, I don’t know if this will ever be a feature. It sounds like something they can do, but it is also very risky if the conditions aren’t perfect. I’m personally OK if they don’t put the tank turn feature in, it’s a cool gimmick but obviously not very useful. I would be more interested to see if they could ever do rear wheel steering, or the crab walk like the GMC Hummer EVs or if they would require additional hardware
I can't imagine how it could function without completely different hardware in the rear.
 

sevengroove

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Based on my reading of it and some other comments I’ve seen, I don’t know if this will ever be a feature. It sounds like something they can do, but it is also very risky if the conditions aren’t perfect. I’m personally OK if they don’t put the tank turn feature in, it’s a cool gimmick but obviously not very useful. I would be more interested to see if they could ever do rear wheel steering, or the crab walk like the GMC Hummer EVs or if they would require additional hardware
I agree, rear wheel steering is far more useful especially for how large these vehicles are. I am shuddering thinking about how I'm going to tackle the mini roundabouts here on Seattle's residential streets, and fully anticipate needing a multi-point turn to navigate a few of them in the R1S.
 

Sean

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I'm in the camp for I'd love to get it but I understand the complexity and the only surprising thing is that they put out the feature in the first place without having a lot of it worked out.
 

crashmtb

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Based on what my focus RS will do just by varying the speed of each rear wheel… rivian’s own “drift mode” will be more than enough for hooligans purposes, and should get pretty close to zero turning radius with enough right foot 🤣
 

sevengroove

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Put it all together, and Tank Turn is really only easy to do in the middle of a big, flat, slippery field. Making it work anywhere else is a big challenge. The places a Tank Turn would actually be useful off-road are never level, wide-open spaces.
This is really the crux of the issue. Makes total sense to delay until they figure it out.
 

Forager1

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I agree, rear wheel steering is far more useful especially for how large these vehicles are. I am shuddering thinking about how I'm going to tackle the mini roundabouts here on Seattle's residential streets, and fully anticipate needing a multi-point turn to navigate a few of them in the R1S.
That’s easy. Here’s what I do in my Supercrew Long-bed F150: for right turns and straight pass through you go the normal way ( counter clockwise). For left turns, you get close to the intersection and verify no traffic and then go clockwise. I think the R1T wheel base is small enough it won’t be a problem, but If it is then that’s how you do it.

Edit: directionally challenged
 
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sevengroove

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That’s easy. Here’s what I do in my Supercrew Long-bed F150: for right turns and straight pass through you go the normal way (clockwise). For left turns, you get close to the intersection and verify no traffic and then go counter clockwise. I think the R1T wheel base is small enough it won’t be a problem, but If it is then that’s how you do it.
I think you might have gotten the counter/clockwise directions mixed up but yea, I think that might have to be the solution. The one thing I dislike as a pedestrian about those left turns is that it is hard to anticipate when a vehicle is about to pull one, especially if the driver is not paying attention to pedestrians. It happens very rarely in my experience, to be fair. With all vehicles meant to go in one direction, it's easier to predict how/when to cross the street.
 

Forager1

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I think you might have gotten the counter/clockwise directions mixed up but yea, I think that might have to be the solution. The one thing I dislike as a pedestrian about those left turns is that it is hard to anticipate when a vehicle is about to pull one, especially if the driver is not paying attention to pedestrians. It happens very rarely in my experience, to be fair. With all vehicles meant to go in one direction, it's easier to predict how/when to cross the street.
Gah! Yes, you are right and I’ve corrected that. I agree, it’s uncommon that peds or another vehicle approach these small residential intersections at the same time as my need to left turn. If it’s a pedestrian I wave them through (they have right of way anyway). If it’s a vehicle, you just have to bite the bullet and do a 3 point turn or mount a curb.

Regarding tank turn, I’ve wondered for a while if the issue with rolling it out wasn’t likely due to the underlying physics of making 4 wheels tank turn (which have to break static friction), versus 2 tank treads (which constantly maintain static friction). This is probably why we see K-turn being emphasized as a preferred solution —it’s more practical in real world use and in design application.
 
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