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rolling back and forth on small hill

Discussion in 'Model S: Driving Dynamics' started by demundus, Aug 27, 2015.

  1. demundus

    demundus Member

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    I never thought this to be bad until the car attempted to shut down via "Pull over safely" message:

    Sometimes, when I'm on a small incline at a stop light, I will let the car roll back and forth out of boredom (much like with a manual ICE, engaging the clutch to move forward and disengaging to roll backwards). I'd say this happens once or twice a week... yesterday I was waiting at a stop light and rolled back and forth about 4 times, causing the car to throw some kind of limp mode on the 5th roll. I quickly put it in park and back into drive and all was good.

    Guess I won't be doing that anymore, anyone else ever run into this issue by doing the same (stupid) thing? :)
     
  2. cottylowry

    cottylowry 2013 Model S

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    NO, never, I didn't want to burn up the clutch.
     
  3. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    I use that method to park every day. No problems in 2.5 years. Of course it's seldom more than one cycle.
     
  4. demundus

    demundus Member

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    I actually use it to park everyday as well! Forgot to mention that, back in, slow roll forward and reback in...

    I guess I was just being dumb with rolling around a lot.
     
  5. Max*

    Max* Autopilot != Autonomous

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    I have NEVER done that on my manual. That uses/burns the clutch for no reason.

    I never do this in the Tesla either. Though I caught my wife trying to hold the car with the go pedal on a hill (she almost got it, but did have some rolling back and forth). I told her to stop, but no errors thrown.
     
  6. brec

    brec Member

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    What harm does holding with the go pedal do? (Asking, not arguing)
     
  7. Max*

    Max* Autopilot != Autonomous

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    I don't have an answer. I asked her to stop because I didn't know if it did any harm or not, and it's just as easy to hit the brakes.

    Best case you're wasting kwh and worst case (like in the OPs) you get an error message thrown at you?
     
  8. ProSkeptic

    ProSkeptic Member

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    My best guess? The car wigged out because you were doing something that Tesla's development crew never bothered to try.

    I'd bet good money that you did no harm.
     
  9. Zextraterrestrial

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    if that is the case they need a new crew that tests more things.
     
  10. Lex

    Lex Member

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    And they're adding more of us Model S drivers every day :cool:

    Maybe send a bug report, does anyone bother ? I've only done 2 in 2 months.. then again not a lot o' bugs IMHO.
     
  11. ProSkeptic

    ProSkeptic Member

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    Well, yeah... that's what makes Tesla different from Legacy carmakers.
     
  12. doug

    doug Administrator / Head Moderator

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    Using an electric motor to hold the car stationary, or to oscillate around stationary, can use quite a bit of current so I wouldn't be surprised if the motor would start to overheat. This is a situation where it's better to use the brakes.
     
  13. Zextraterrestrial

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    #13 Zextraterrestrial, Aug 27, 2015
    Last edited: Aug 27, 2015
    haha the speak a bug report is pretty buggy. It would be nice if it replayed your report for you maybe so you'd know it did something

    - - - Updated - - -

    really, even with the liquid cooling while being stationary? (power 'meter' shows ~1-2kW ...@ ~400V =~5A or is that wrong?)
    I agree, use the brakes, but...curious
     
  14. ProSkeptic

    ProSkeptic Member

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    Holding the brakes (on hydraulic pressure only) requires zero output from the battery.

    Any other method of stationkeeping requires some output.
     
  15. doug

    doug Administrator / Head Moderator

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    Sure. There's a difference between stationary on flat ground and stationary on an incline.

    I'll leave the math as an exercise for those interested, but here's how to look at it: Consider how much torque the motor must produce for given about of acceleration on flat ground. Producing that torque requires current and that current causes Joule heating. Now consider the car stationary on an incline. The car isn't moving, but without the brakes, the motor must produce enough torque to counteract the acceleration due to gravity (or fraction thereof given the slope of the hill). Obviously, the more steep the hill, the higher fraction of gravity you have to counteract and the more current the motor will require.
     
  16. dhrivnak

    dhrivnak Active Member

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    You are holding the motor in a stall state which normally creates a lot of excess heat. This is bad to do in any car but stalled electric motors are likely the worst. I was told by a DC motor engineer one could burn up a motor in just a few minutes doing this. And yes it is terrible for a clutch as well.
     
  17. tstafford

    tstafford Member

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    Love these boards. I was on a hill, in traffic yesterday and was wondering about this exact thing. The car clearly has a "hill hold" feature that it somehow applies so that you don't roll back at all during takeoff. It holds for just a moment and then lets the car roll back. I then played with keeping it stationary with the go pedal - and wondered if this was bad.

    The thread has me convinced just to use the brake - which I hate because I'm having fun seeing how little I can use it (just for sport).
     
  18. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Well, it definitely uses more energy than the brake does, and I suspect there could be a cooling issue as well. For parking, when you are only adjusting your position once or twice at most, there's no problem. Using it as a hill-hold could lead to issues.

    The hill assist uses the parking brake, not the motor.
     
  19. Chris TX

    Chris TX Active Member

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    Going back and forth like that could cause the hill-hold feature to think it's having a problem. You also could have been at the "long tooth" area on the wheel position sensor so it could have thought one of the wheels was going the other direction and something was really wrong. The computer did its job and played it safe. Stop jacking with the car, man! :tongue:
     
  20. Thud

    Thud Member

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    Using the motor to keep the car stationary on a small hill would use about as much current as accelerating gently on a flat surface. It was probably more a matter of the computer getting confused by unusual/unexpected data so it erred on the side of safety.
     

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