Rivian announces Tank Turn feature

[ajdelange]

Please excuse my ignorance but how does this work? The wheels don't appear to be turning. Hmm...

In a video there is a strobe effect from the framing so you can't reliably judge wheel spin from video. The general principle is that as you have independent torque control on the four wheels you can apply rearward force to the passenger side of the car and forward force to the drivers side. Both of these put a clockwize (looking down ) torque on the vehicle and it will, thus rotate clockwize. As the vehicle is being pushed simultaneously forwards and backwards it is clear it won't be going anywhere and that, therefore, there will be considerable slip at each of the four wheels. This is why you must do this in mud only.

I actually think this is very dumb. Can someone please elaborate what makes this so useful?

Practically speaking this is going to be about as useful as the "Emissions Mode" in the Tesla. What this video does is demonstrate superb control over torque/slip at each of the four wheels. This has lots of implications (all good ones) with respect to control of under and over steer (i.e. lateral stability) over a wide range of substrate conditions (wet, dry. ice, snow, grave, mud.....).

Advertisement

 

[Mule Ferguson]

Back up and do a bootlegger turn. This was perfected by bootleggers here in NC to get away from the law. my friend JR Johnson was famous for it.

 

[martinsky]

You should be able to perform slow tank turns with the twin motor CT. It would need to be a function you could select from the screen. It would be really useful for some tight parking situations and would work like this.
Slow tank turn right: Brake right wheels, roll left wheels forward 4". Brake left wheels, roll right wheels back 4". Repeat.
So for instance on the screen you would select tank turn 90 degrees, 180 degrees or 270 degrees.

 

[TyPope]

I actually think this is very dumb. Can someone please elaborate what makes this so useful?

A long time ago... I was driving down a narrow abandoned logging road in my '65 Mustang. Now, you don't normally drive along looking for trouble in a classic Mustang but there I was. Needless to say, it took a bulldozer to pull me out. There wasn't room to turn around and I was face forward down a slippery slope. I would have loved to be able to turn around in place there rather than the hell storm that came after that. Granted, that's pretty isolated but I can definitely see some use for being able to flip it around like that. Not often, and hopefully REALLY not often but having the capability would be neat. Plus, it'd be a great party trick!

 

[Ehninger1212]

A long time ago... I was driving down a narrow abandoned logging road in my '65 Mustang. Now, you don't normally drive along looking for trouble in a classic Mustang but there I was. Needless to say, it took a bulldozer to pull me out. There wasn't room to turn around and I was face forward down a slippery slope. I would have loved to be able to turn around in place there rather than the hell storm that came after that. Granted, that's pretty isolated but I can definitely see some use for being able to flip it around like that. Not often, and hopefully REALLY not often but having the capability would be neat. Plus, it'd be a great party trick!

Did you try reversing? If it was that slippery i doubt tank turning would have made a difference, MAYBE you would have managed better traction form the shift in weight going the opposite direction but who knows? Don't get me wrong, i can see the very very rare occasion this could be somewhat useful.. but it mostly just seems like a gimmicky feature.

 

[TyPope]

Did you try reversing? If it was that slippery i doubt tank turning would have made a difference, MAYBE you would have managed better traction form the shift in weight going the opposite direction but who knows? Don't get me wrong, i can see the very very rare occasion this could be somewhat useful.. but it mostly just seems like a gimmicky feature.

I did. It just spun. It had a 351 Windsor in it but that C4 transmission would just spin one tire. There was no weight in the back but I thought if I could just get the rear downhill that there would be enough weight transfer to get up the hill. As soon as I crested that hill slowly, I hit the brakes and STILL slid forward 20 feet or so. We put pine branches under the tires to no avail. we finally got it backed up just enough to be aimed straight ahead. My brother and a friend who were pushing jumped in and I gunned it down the hill, across a narrow patch over a culvert pipe and about half-way up the other side. Again with tree branches but the darn thing just wouldn't move. One buddy went for help and came back with the neighbor and his front end loader. Even he had to go around me and into the woods just to get enough traction to get me out of there. It was quite the scandal at the time. (1988 probably) Come to think of it, tank turn probably wouldn't have helped then.

 

[Sirfun]

I did. It just spun. It had a 351 Windsor in it but that C4 transmission would just spin one tire. There was no weight in the back but I thought if I could just get the rear downhill that there would be enough weight transfer to get up the hill. As soon as I crested that hill slowly, I hit the brakes and STILL slid forward 20 feet or so. We put pine branches under the tires to no avail. we finally got it backed up just enough to be aimed straight ahead. My brother and a friend who were pushing jumped in and I gunned it down the hill, across a narrow patch over a culvert pipe and about half-way up the other side. Again with tree branches but the darn thing just wouldn't move. One buddy went for help and came back with the neighbor and his front end loader. Even he had to go around me and into the woods just to get enough traction to get me out of there. It was quite the scandal at the time. (1988 probably) Come to think of it, tank turn probably wouldn't have helped then.

Great story, thanks for sharing.

 

[martinsky]

I actually think this is very dumb. Can someone please elaborate what makes this so useful?

It would be really useful to park the CT in the parking bay beside my driveway. I'm actually not even sure I could get the CT into the bay without the tank turn feature. I park my Triton ute there now which is a really tight squeeze, but the CT has a wheelbase that is 32" longer than the Triton, which means it will have a pretty large turning circle, and be difficult to get into that bay.
So that's one example of how useful a slow tank turn feature would be. In fact I think the tank turn feature would be used more for parking in tight spots than anything else.

 

[ajdelange]

A tank turn requires forward thrust on one side of the vehicle and reverse thrust on the other. Setting this up on a low slip surface will clearly destroy tires. There is a definite caveat concerning this in all the Rivian videos etc. about this feature. It is only to be used in loose mud, gravel, sand etc. It is definitely a promotional feature rather than a practical one.

 

[martinsky]

A tank turn required forward thrust on one side of the vehicle and reverse thrust on the other. Setting this up on a low slip surface will clearly destroy tires. There is a definite caveat concerning this in all the Rivian videos etc. about this feature. It is only to be used in loose mud, gravel, sand etc. It is definitely a promotional feature rather than a practical one.

Well that is one way to do a tank turn, but there is another way which I described. It is actually a maneuver I often perform on my own mini-excavator. I find that when I am in really tight spots, and I need to carefully avoid smashing the boom into something like my house, I will inch the left track forward a bit and then inch the right track back a bit, and I will repeat this until I am in the required position.
So while moving one side of the vehicle's wheels at a time, is not as spectacular as the Rivian spinning tank turn, it's not really required for tight maneuvering. By applying brakes to the left side and then rotating the right wheels forward a little, followed by braking the right side and rotating the lefts wheels rearwards a little, you obtain the tank turn effect. And this is exactly what is done with excavators to perform tight turns.
As for tire wear, it would be no worse on the front tires than any tight parking maneuver where you change wheel direction while stationary. And as the maneuver would be under slow speed, this would reduce the level of heat and friction applied to the tires.

My prediction is that it is such an obviously useful feature for a twin motor EV, that it will become standard in due course.

 

[Ehninger1212]

It would be really useful to park the CT in the parking bay beside my driveway. I'm actually not even sure I could get the CT into the bay without the tank turn feature. I park my Triton ute there now which is a really tight squeeze, but the CT has a wheelbase that is 32" longer than the Triton, which means it will have a pretty large turning circle, and be difficult to get into that bay.
So that's one example of how useful a slow tank turn feature would be. In fact I think the tank turn feature would be used more for parking in tight spots than anything else.

Lol, i cant wait to see what happens when people activate this feature on pavement.?

 

[TyPope]

It would be really useful to park the CT in the parking bay beside my driveway. I'm actually not even sure I could get the CT into the bay without the tank turn feature. I park my Triton ute there now which is a really tight squeeze, but the CT has a wheelbase that is 32" longer than the Triton, which means it will have a pretty large turning circle, and be difficult to get into that bay.
So that's one example of how useful a slow tank turn feature would be. In fact I think the tank turn feature would be used more for parking in tight spots than anything else.

You bring up a good point. My F350 Platinum Crewcab long bed truck... 22' long has the turning radius of an aircraft carrier. I had an equally long F-450 dually before it that would turn around on a dime. I actually did a U-turn on a 2 lane road T intersection one time! I know that the 450 had "I-beam front end that pushed the wheels outwards a couple of inches which allowed the wheels to turn sharper than most. Is there a reason the CT can't have a great turn radius? I know the motors connect to the wheels about the same way but it seems that without an engine between the front wheels, Tesla would be able to move the suspension stuff inwards a little bit to help us make tight maneuvers.

 

[ajdelange]

Common sense will rule - Tesla seems to have it.

What is being discussed is generally called "torque vectoring" and is realized by applying differential thrust. This can be done by adding (motors) or subtracting (brakes) thrust. Obviously Rivian, with its 4 independently controlled motors, has the most sophisticated torque vectoring with its 4 independent motors. The Tesla TriMotor will be reasonably close with two motors in the rear and differential braking in the front. The dual motor will have somewhat less and the single motor less still but there is fundamentally no reason the single motor can do some torque vectoring too. Pin the right rear wheel and apply torque to the rear motor. There is then torque around the right rear wheel which will try to rotate the vehicle clockwise and push it forward. Now pin the left and put the vehicle in R. More clockwise torque trying to turn the car on its left wheel while dragging it back.

 

[Sirfun]

You bring up a good point. My F350 Platinum Crewcab long bed truck... 22' long has the turning radius of an aircraft carrier. I had an equally long F-450 dually before it that would turn around on a dime. I actually did a U-turn on a 2 lane road T intersection one time! I know that the 450 had "I-beam front end that pushed the wheels outwards a couple of inches which allowed the wheels to turn sharper than most. Is there a reason the CT can't have a great turn radius? I know the motors connect to the wheels about the same way but it seems that without an engine between the front wheels, Tesla would be able to move the suspension stuff inwards a little bit to help us make tight maneuvers.

Check out the rides during the reveal. The CT turns very tightly.

 

[martinsky]

Check out the rides during the reveal. The CT turns very tightly.

Going by this test drive - - I would say curb to curb turning circle of over 40 feet, which would be good considering it's wheelbase length.