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Will Model X have all-wheel steering?

Discussion in 'Model X' started by DaveT, May 24, 2014.

  1. DaveT

    DaveT Searcher of green pastures

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    I was watching a bunch of Model X videos from 2012 when it was revealed and in one interview Elon Musk mentioned that the Model X has an amazing turning radius, comparable to a MINI.

    I initially thought that this was because of the two motor, AWD system. But I'm thinking that if the rear wheels don't steer then a MINI-like turning radius won't be possible.

    So, I'm thinking that the Model X might have all-wheel steering (not just AWD) so the rear wheels will steer when needed to help increase turning radius. The overall effect will be that the Model X will feel like a much smaller car to handle, especially in parking lots.
     
  2. MikeL

    MikeL some guy

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    This is the first mention of it that I have seen. Has the ring of "more delay" to it :wink:.

    There was a car (Cadillac ?) a couple of years back that had 4 wheel steer. Rears went opposite, "roundy" at low speed, and slightly with, "crab" at highway speed. Interesting. Don't need it.

    my Model S test drive started and ended in a very tight parking garage with crazy amounts of traffic. It did not seem too big, more maneuverable than its actual (large) size made me expect. Point is, same platform, should be fine. It is BIG tho. ML
     
  3. mrdoubleb

    mrdoubleb Active Member

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    I've only seen rear wheel stearing implemented on huge trucks and buses - especially on articulated city buses over here, so they can still take the turns in the downtown area.
    I suppose if Tesla did it it would be completley electronic and computer controlled - probably with an extra electric motor in the back to steer the rear wheels. Still seems like a rather complicated "extra". I wonder if it would improve anything about off road capabilities or high speed highway driving (in curves). That may be a more compelling reason than simply to assist parking.
     
  4. SCW-Greg

    SCW-Greg Active Member

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    4wheel steering goes as far back 1987, via Honda. Concept was good, yet played out so subtle, that consumer demand never took hold. And has been dropped by nearly (if not) all manf.

    Steering - Wikipedia, the free encyclopedia
     
  5. RDoc

    RDoc S85D

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    We had a Honda Prelude with mechanical all wheel steering which we really liked a lot. I don't think most people were very enthusiastic about it though.
     
  6. Vger

    Vger Active Member

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    Actually, I was at the reveal event and rode in the prototype. One of the young design engineers was our driver. He said that the tight turning circle (tighter than Model S, despite longer wheelbase) was indeed due to the ability to control the torque delivered to each of four wheels independently. Apparently, even without actually steering the rear wheels, this "torque-steer" is sufficient to twist the car faster than otherwise possible!
     
  7. SCW-Greg

    SCW-Greg Active Member

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    Interesting. Reducing scrub no doubt, and improving rolling efficiency I would think.
     
  8. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    Small turning radiuses are particularly handy for taxis...
     
  9. DaveT

    DaveT Searcher of green pastures

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    Wow that's really interesting. If they're able to gain a tight turning radius due to torque control in each wheel (without the rear wheels turning), that's amazing. Perhaps when making a u-turn the car will give additional torque to the right front and right rear wheels, thus giving it a tighter turning radius. Anybody have thoughts on this? Has this ever been done on a car before?
     
  10. scottf200

    scottf200 Active Member

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    I assumed when this was state it was done with "braking the rear inside wheel".
    Image from below article just to show a visual of tires (obviously not Model X with electric motors being displayed).
    fF8i5c8.png
    What is the basic of cutting brake and its working operation ? - BajaTutorBajaTutor
     
  11. Johan

    Johan Took a TSLA bear test. Came back negative.

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    The Rimac Cocept_one and electric SLS both have this. They have individual motors on each wheel but the concept is the same. Mercedes calls is "torque vectoring". Chris Harrison talks about it in his video review of the SLS and says it makes a huge difference on the track. So why not also at low speeds for tight turns? (Obviously neither the Rimac nor SLS turn on the rears).
     
  12. ModelX

    ModelX Member

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    I believe my Mitsubishi 3000 GT had this. That car could go anywhere!
     
  13. vgrinshpun

    vgrinshpun Active Member

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    I do not think it is possible to directly control the torque delivered to each individual wheel, because each of the two motors is connected to two wheels. The only way I can see it is possible to implement on MX is to use ABS system to brake one (inside rear) wheel, allowing more torque to be delivered to the right outside wheel. This is essentially mechanical system.

    The mechanical torque control systems are usually employed for higher speed stability, rather than increased maneuverability in tight parking spaces. My wife's Acura MDX has this system which works great for high speed cornering.

    I strongly suspect that tighter turning radius in MX is achieved via increased steering angle.

    - - - Updated - - -

    I absolutely love Merc. SLS electric video with Chris Harris - watched it few more times that I should have. :smile: I think that eventually individual torque control to each individual wheel via individually coupled electric motors will completely replace contemporary mechanical stability systems, while immensely improving effectiveness for stability control systems. Response time will improve by two orders of magnitude! Interestingly, the contemporary vehicle dynamic control systems were originally introduced by Mercedes.

    The MX, however, will have two motors, not four as Merc. SLS electric, so individually controlling the torque to each wheel in a way it is done in Merc SLS is not possible.

    Mercedes SLS Electric Drive. Can Volts Ever Match Pistons? - /CHRIS HARRIS ON CARS - YouTube
     
  14. Nubo

    Nubo Test Mule

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    Maybe a bit of Ron Popeil showmanship in that statement. Iirc, the Mini's turning radius isn't all that spectacular though of course everyone assumes it would be because it's small.
     
  15. MikeL

    MikeL some guy

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    Take ONE day off from the TMC (didn't make it a whole day apparently) and I miss so much cool stuff :smile:
     
  16. DaveT

    DaveT Searcher of green pastures

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    I think it's possible for Tesla to achieve torque control for each wheel by utilizing the brakes to apply to just a single wheel. So in case of a u-turn, they could use the brakes on the left rear wheel while the rest of the car uses the torque from the two motors (ie., front motor to left/right front wheel and rear motor to left/right rear but left rear is muted by the application of the brake on the wheel).

    In other scenarios (ie., when one wheel needs more torque) the car could apply brakes to 3 wheels and the remaining wheel would get more torque.

    However, I'm guessing there's a better way to achieve this by actually using the brakes. Maybe they've come up with something that has the same effect but without the use of the brakes.
     
  17. Johan

    Johan Took a TSLA bear test. Came back negative.

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    One motor going to two wheels should be able to 1) modulate total torque of the motor (duh) and 2) modulate how much torque goes to left vs. right wheel. Combine 1 + 2 and it's the same effect (almost) as having four motors?
     
  18. vgrinshpun

    vgrinshpun Active Member

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    How is a *motor* that directly connected to *two* wheels via a reduction gear/differential can modulate how much torque each individual wheel is receiving?
     
  19. Johan

    Johan Took a TSLA bear test. Came back negative.

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    The same way Model S does now on the rears with traction control? If my rear right tyre is on ice and the left is on asphalt TC will direct torque to only the left? And it's not mechanically braking on the right? My experience in winter is that if there is no grip on any of the rears I can floor the pedal but the kW gauge barely moves.
     
  20. vgrinshpun

    vgrinshpun Active Member

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    #20 vgrinshpun, May 26, 2014
    Last edited: May 26, 2014
    As I mentioned in my original post, the motor can not control torque split between the left and right wheel while it is connected to both via the reduction gear/differential. It can be done only by applying brakes to one of the wheels, which forces the open differential to transfer the torque to another wheel. This is conventional mechanical system that is employed on many cars and really has nothing to do with the motor (2004 Toyota Sienna AWD which I owned a while back had this system).

    The advantage of the electric motor combined with the above described mechanical system is in response time of the total torque that produced by the motor, it is almost two orders of magnitude faster than for an ICE power train. Elon mentioned several times that response of the MS/MX power train is in milliseconds.

    Just to put some numbers on the Elon's milliseconds comment, if response time is two milliseconds, the electric drive train of a car traveling at 55 mph can respond to the detected slip condition after moving only 2 inches after detecting it.
     

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