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Does the S steer by wire?

Discussion in 'Model S: Driving Dynamics' started by D.E., Jul 12, 2017.

  1. D.E.

    D.E. Member

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    Does the S steer by wire? I'm trying to rationalize the comfort/normal/sport steering ratio options.

    David
     
  2. kirkbauer

    kirkbauer Member

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    That's a good question. I'm not a car guy, but I'm assuming it affects how much the power steering amplifies your inputs. But I think it is direct steering like most (all?) cars with power steering assist like most (all?) modern cars.
     
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  3. rabar10

    rabar10 FFE until Model 3

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    The steering wheel is still mechanically connected to the front wheels, so it's not 'steer by wire'.

    The "steering feel" options control the amount/feel of power-assist steering assistance. The steering ratio i.e. how far the wheels turn when you turn the steering wheel, does not change, as it's fixed by the rack-and-pinion gearing and front suspension setup.
     
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  4. Pezpunk

    Pezpunk Member

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    this has been a feature on luxury cars for a long time -- i owned a 1986 Lincoln with a slider that controlled the feel of the power steering.
     
  5. sandpiper

    sandpiper Active Member

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    It is capable of steering by wire (autopilot), but when steering manually the servomotor is only used to amplify driver steering input. In the event that the servo-steering fails, which happened to me a few weeks ago, you can still steer manually, but holy hell, it's tough. You literally need to grip the wheel with both arms and reef the wheel around in order to make a 90 degree corner.
     
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  6. Saghost

    Saghost Active Member

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    The steering is still mechanically connected, through a rack and pinion system.

    There's a second rack on the passenger side, with another pinion attached to an electric motor.

    This motor steers the car under autopilot, and provides the steering assist the rest of the time.

    On current Tesla cars, the different steering options change only the amount of assistance provided by the motor.

    (There are some cars that change the actual steering ratio mechanically - Audi has a gear motor two speed setup in some cars. Only one car I know of that's truly drive by wire, the Infiniti Q50. Folks have said that driving it can be disconcerting at times.)
     
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  7. mrElbe

    mrElbe Active Member

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    A pure "steer by wire" would make it impossible to steer during an electrical failure.
     
  8. sandpiper

    sandpiper Active Member

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    As I understand it, Tesla uses one of Bosch systems in the linked document.

    http://www.bosch-mobility-solutions.us/media/documents/a-product-brochure-servolectric.pdf?WT.mc_id=200_DE_OEM_OEM

    I had thought it was the 3rd unit (paraxial), but your text seems to imply that it's the second (servo on second pinion).
     
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  9. Saghost

    Saghost Active Member

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    I haven't actually had the assembly apart - I'm regurgitating from what I've been told in the past. If you have specific information suggesting it's the third, go with it. The photos I remember do look more like the third than the second, as well.

    Functionally, it doesn't seem like it matters for the purposes of this discussion or any other I've had - whether it's a second rack and pinion or a separate recirculating ball gear on the passenger side, there's a motor attached to and directly moving the steering rack.
     
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  10. Stiction

    Stiction Member

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    Autopilot is not "by wire". The term implies that there is no mechanical connection AT ALL to the front tires...i.e. that both autopilot and the driver would just be feeding desired wheel position signals to actuators that moved the tires. That is not the case. Instead as you point out there are electric assist motors to change the driver feel, and also probably used for autopilot.
     
  11. clostridium

    clostridium Member

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    The Q50 (as someone else noted) has true steer by wire and has a backup rack and pinion system in case of electrical failure. I had a 2014 q50 and actually liked the steer by wire even though it was unpopular amongst auto journalists. One time it failed due to a defect they ultimately fixed with a recall and the backup steering system required significant force to operate. It was like using an old school non-power steering car which is basically what it turned into in that scenario.
     
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  12. Saghost

    Saghost Active Member

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    What did you like about the steer by wire? As you said, all the reviews I've seen were negative...
     
  13. sandpiper

    sandpiper Active Member

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    Meh... I don't argue about definitions. The Model S is is capable of steering entirely under electronic control, whatever you choose to call it. It's more than an assist. And yes, as I noted, it is still mechanically coupled, but it's all but useless when electrical systems are unavailable.
     
  14. u00mem9

    u00mem9 Member

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    :rolleyes: I suggest you refrain from answering questions involving words that have definitions you don't understand. There is no argument, because Steer-by-Wire has a meaning.

    Google is your friend. At minimum, it can let you know when you are out of your depth.
     
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  15. sandpiper

    sandpiper Active Member

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    Oh good grief. Get off your high horse. I think the altitude is affecting your mental processes. If you read my original response I said:

    "It is capable of steering by wire (autopilot), but when steering manually the servomotor is only used to amplify driver steering input. In the event that the servo-steering fails, which happened to me a few weeks ago, you can still steer manually, but holy hell, it's tough."

    That is entirely 100% correct. The vehicle is completely capable of steering by wire. Is it a "steer be wire system" in the Airbus aircraft sense, where there is no mechanical link between the pilot control stick and the mechanical actuators? No... and I didn't claim it was.
     
  16. Saghost

    Saghost Active Member

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    His tone may have been abrasive and inflammatory, but his message was correct.

    Steering automatically under computer guidance is separate and unrelated to steer by wire, and either is possible without the other.
     
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  17. sandpiper

    sandpiper Active Member

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    Yes... of course. And my stating that the Tesla was capable of "steering by wire" is and remains correct. It is capable of steering the vehicle without any input from the driver other than electrical or electronic signals. No, it is not a "steer by wire" system, because of the mechanical linkage in the Bosch system.

    And yes, "steer by wire" does not necessarily imply computer control. I suppose you could have a wheel/yoke/joystick actuating potentiometers that are directly connected to a servo system, and with no intervening computer control. But, I'm not aware of anybody doing a system like that, and don't know why your would. Maybe in some pre-1970s military aircraft? Although I had thought that all of those used electro-hydraulic controls/logic.
     
  18. clostridium

    clostridium Member

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    Steering feel is subjective. I liked the feel and I liked how it would compensate for crosswinds and imperfections in the road without you moving the wheel. It reduced fatigue on long drives. I also liked how you could easily make changes in the steering speed and fee.
     
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  19. Saghost

    Saghost Active Member

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    Again, steering under computer control is not steer by wire.

    The "by wire" words have been established to describe the connection between the human's control input and the output.

    Thus, a 1980s car with cruise control isn't drive by wire - it has a mechanical connection between the pedal and the throttle body/carburetor, and it isn't said to be drive by wire even when the cruise control is engaged and an actuator is dragging the cable around.

    An aircraft with full authority automated flight controls and a mechanical hydraulic control system for the pilot is not fly by wire - one with identical automated controls that uses transducers to read the pilot's input and runs them through a computer which drives the same hydraulic actuators is.

    My Tesla can apply the brakes automatically under computer control, but it isn't brake by wire, because the pedal hooks directly to the master cylinder (Mercedes dabbled in brake by wire in the early 2000s with a few models.)

    Aside from the existence of a backup system, I don't see how you can have a part time steer by wire system, because it's all about how the pieces are hooked together.
     
  20. sandpiper

    sandpiper Active Member

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    Yes, yes, all good. I've been designing electro-mechanical & computer control systems for 25 years, and I've been a pilot nearly as long. I'm well aware of the difference between mechanical, electrical and digital/computer control systems, all of the various transducers, sensors, actuators and so on. And I'm well aware of what a FADEC system is in relation to both aircraft and cars.

    My original comment, which has apparently tweaked the sensibilities of some rather tightly wound participants, was directed to the OP. I interpreted the original question to mean "does it steer under electronic control", as they were asking about the different comfort settings. My intent was to state that the Tesla could steer entirely under electronic control, with no mechanical operator input, and so it can. But I also stated when driving manually, it does not. In that case, the servo only acts as an input amplifier. And so it does.

    With that said, I've spent WAY too much time discussing this silliness. I'm done.
     

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