Will Model X have all-wheel steering?

[alin3]

If the MX has 4 wheel steering, that would be fantastic!. The new 911 GT3 with rear wheel steering is the most amazing handling car I have ever driven. It's ability to "shorten the wheel base" during slow maneuvers by turning opposite of the front wheels was uncanny and taking high speed turns was like cutting with a scalpel. It would fantastic also on a big heavy car like the MX.

http://www.porsche.com/usa/models/911/911-gt3/chassis/rear-axle-steering/

 

[Macgaver]

Correct me if I am wrong, but "torque vectoring" is for high speed steering performance right ? Like on track ?

When compared to mini, it was more related to easy city driving/parking (I believe)

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Ho ! just found that the four wheel drive version of the mini 2012 (the countryman) had a turn radius of 38 ft !!!

I think we have a potential answer here. 37 ft will be better than "a mini" after all !

 

[stopcrazypp]

Hasn´t Tesla always said that the MX would be built on the same platform as the MS? IMHO that would rule out any changes but some kind of torque vectoring (no matter how it is achieved) which is basically software. That would mean small improvements to handling under speed but not a decrease in turning radius at low speeds.

Negative torque vectoring where one wheel can apply torque in the opposite direction of the other one can reduce the turning radius of the car (think of how a tank turns). This is possible in cars like the SLS E-Cell where there are independent motors on the two sides of the car (4 motors total, one per wheel). I'm not sure if it's possible to approximate this with the independent front/rear motors and using the brakes on the wheels in the opposite corners.

 

[AnxietyRanger]

FWIW, using brakes/ESP to simulate partially the effect torque vectoring is quite commonly used as an electronic limited slip differential (I'd expect the Model S does it already too) - and just as commonly it is considered crap compared to mechanical limited-slip differentials, which are usually the domain of sporty models.

So, I doubt just using individual wheel brakes would create satisfactory torque vectoring. Individual motors in wheels, of course, would be the ultimate solution - probably exceeding what mechanical differentials can do.

 

[stopcrazypp]

FWIW, using brakes/ESP to simulate partially the effect torque vectoring is quite commonly used as an electronic limited slip differential (I'd expect the Model S does it already too) - and just as commonly it is considered crap compared to mechanical limited-slip differentials, which are usually the domain of sporty models.

So, I doubt just using individual wheel brakes would create satisfactory torque vectoring. Individual motors in wheels, of course, would be the ultimate solution - probably exceeding what mechanical differentials can do.

Not sure if you are referring to my post, but I'm aware of brakes already being in use to simulate torque vectoring. What I'm talking about is more complex than that (negative torque vectoring). Basically I'm talking about for example if you wanted to turn left:
Have the front motor spin forward and brake the front left wheel and have the back motor spin backwards and brake the rear right wheel to try to turn the vehicle and reduce the turning radius. I'm not sure if this would actually work properly to simulate negative torque vectoring.

It's much easier to have negative torque vectoring when you have independent motors per wheel. In the above case, you just spin the motors on the right forward and the motors on the left backwards. There are electric ATVs that achieve zero radius turns this way:
http://www.greencarcongress.com/2014/01/20140127-evdrive.html

 

[AnxietyRanger]

The effects of four wheel steering on most contemporary cars is very subtle.

I wonder if this is accurate of the Porsche system, of a slow-speed turn?

I tried looking at the LeftLane news gallery, one of the highest-resolution series we have a turning Model X mule:

http://www.leftlanenews.com/photos/large/tesla-model-x-picture-8-1.html

http://www.leftlanenews.com/photos/large/tesla-model-x-picture-10-1.html

It is probably just the shadows, but of course if one really tries (read: wants to believe), one can think the rear wheels are a little turned.

The best turning videos of Model X mule, I believe, are these but the rear wheels are obscured by cars and lighting in the crucial moments:

Tesla Model X Prototype May 8 2015 - YouTube

Tesla Model X Prototype May 8 2015 - YouTube

Tesla Model X May 8 2015 - YouTube

I guess on the second video one can imagine seeing the left rear wheel turned inwards right before the red car blocks the view, but that is probably just the angle and the video quality...

Overall, I see no evidence of rear-wheel steering on the Model X mules, but I guess we can't say for 100% it would be impossible?

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Not sure if you are referring to my post, but I'm aware of brakes already being in use to simulate torque vectoring. What I'm talking about is more complex than that (negative torque vectoring). Basically I'm talking about for example if you wanted to turn left:
Have the front motor spin forward and brake the front left wheel and have the back motor spin backwards and brake the rear right wheel to try to turn the vehicle and reduce the turning radius. I'm not sure if this would actually work properly to simulate negative torque vectoring.

It's much easier to have negative torque vectoring when you have independent motors per wheel. In the above case, you just spin the motors on the right forward and the motors on the left backwards. There are electric ATVs that achieve zero radius turns this way:
http://www.greencarcongress.com/2014/01/20140127-evdrive.html

Thank you for the interesting posts, stopcrazyapp. My reply was directed a no-one in particular, just idle musings. I definitely get your point.

 

[EarlyAdopter]

Perhaps they have more room on the Model X to use an active electronic rear differential, ala Audi's Sports Diff or the aforementioned Acura SH-AWD. These systems allow for transfer of torque left/right even though they're driven by a single input shaft (I.e. motor), without using the brakes as in conventional EDL systems.

This video explains how the Audi system works. I had it on my 2010 S4 and it felt like the hand of God reaching down to help push the car around corners. Really defied the laws of physics.

 

[AnxietyRanger]

Audi's sport diff is indeed nice, I've had it too.

 

[EchoDelta]

Perhaps they have more room on the Model X to use an active electronic rear differential, ala Audi's Sports Diff or the aforementioned Acura SH-AWD. These systems allow for transfer of torque left/right even though they're driven by a single input shaft (I.e. motor), without using the brakes as in conventional EDL systems.

This video explains how the Audi system works. I had it on my 2010 S4 and it felt like the hand of God reaching down to help push the car around corners. Really defied the laws of physics.

True. Although I hadn't made the connection before, with your help now I see Maradona's goal in the World Cup was also torque vectoring pushing the ball around.

 

[jimmyjohn]

Is there any further speculation on 4WS for the X?

 

[tonyx]

RE: Model X Turning Radius:

I am posting here as I didn't find a more relevant thread - does anyone have data on Model X turning radius? It's not in the screen grabs MarkZ posted here: Will MX fit in my garage? - Page 5 - wondering if it's same as Model S 18.5' (37' turning circle).