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Thanks regenerative braking for saving me from a collision.

Discussion in 'Model S' started by AMPd, Dec 2, 2016.

  1. AMPd

    AMPd Active Member

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    Before I get lectured, I know I shouldn't have done what I've done. It was risky and should not be repeated.

    I'm running Michelin PS2 tires on 21 inch wheels.

    My fiancé and I took a trip to Reno last weekend.
    Coming back home there was a huge snow storm, as everyone knows the tires I have do not perform well in the cold.
    And boy did I find that out first hand, AWD did fantastic to keep my car going. However I had absolutely no brakes, the only thing slowing me down was regen.
    I made sure to keep a huge gap up until I came to a sharp downhill turn where I saw slowing down traffic due to a few cars spinning out.

    I let off the accelerator and the car is slowing down, but not fast enough, I try the brakes and nope nothing.
    Thanks to regen my car slowed down enough to where I could swerve onto the snow filled shoulder and come to a stop.
    I was able to get out of that snow, but as I did an indicator light on the dash came on, it's a red SUV with up and down arrows.
     
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  2. cgiGuy

    cgiGuy Active Member

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    Glad you're ok. Weird that the red one came on, as that would indidcate it was put into jack mode. Yellow might indicate a problem.

    Capture.JPG
     
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  3. ev-now

    ev-now Member

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    So regen works by transferring friction between the tire/ground back to the motor and so to the battery. Given sufficient friction to generate any regen, I don't see how the brakes would not work when applied similarly (that's why they want Low regen in adverse conditions, to avoid losing traction).

    Does this mean traction control plus regen provides better tire/wheel control than TC plus brake ??
     
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  4. AMPd

    AMPd Active Member

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    Thank you for that.
    I tried setting the suspension to high when I was trying to get off the shoulder but it would not go up.
    Stayed in normal.
    Even when we got down the mountain and driving at freeway speeds the suspension stayed in normal, I tried selecting low but nothing happened.

    It's all normal now, and I'm glad there was no damage.
    Next time we'll be taking my fiancés RWD s85 on all season tires. At least with those we can chain up.
     
  5. AMPd

    AMPd Active Member

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    I tried the brakes and the car would just slide forward at the same speed.
     
  6. VikH

    VikH Member

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    Your regen didn't do anything but modulate your stopping power to a lower force. A light application of the brakes would equal the same result.
     
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  7. AMPd

    AMPd Active Member

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    It slowed me down when the brakes caused my car to slide.
    And for that I am grateful.
     
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  8. animorph

    animorph Member

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    Sounds like the regen was dialing itself back to exactly match what traction you had. Any added braking was too much. Pretty nice traction design if that was the case.
     
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  9. Barry

    Barry Member

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    I had that same error light come on earlier this week (without any snow issues, just cold), and the suspension continued to worked fine. Called the Svc Center. They said do a reboot and call back if it didn't go away. It's been fine ever since.
     
  10. cantdecide

    cantdecide Member

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    Agreed. Regen doesn't magically improve the traction between the wheels and the ground. So in this case it sounds like the maximum deceleration the tire/snow combination was capable of was slightly less than regen (hence the brakes did nothing) but in a car without regen the brakes would have been able to decelerate at the same rate as what regen could in the Tesla.

    However, having said that it is likely that regen (in the Tesla) applied faster than brakes in a non regen car simply by the fact that "take the foot off the accelerator and push down on the brakes" is going to take a non-zero length of time, in which the Tesla does some regen decelerating. That might only make the difference of 0.3 miles per hour at the start of decelerating, but even a small difference there can lead to a significant difference by the time you stop. Basically you gain the 0.3 miles per hour for the entire time while decelerating, which can be 10 seconds in the snow, which gains you 4 feet in the end.
     
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  11. SageBrush

    SageBrush Active Member

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    My first thought mirrored the other posts that regen is not magic, but it may be more fine tuned than ABS.
     
  12. Yinn

    Yinn Member

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    Possibly. But you forgot the friction/resistance of the motor. Regen uses the motor as a "brake" which is what is causing it to slow down And doesn't actually use the brakes. The force of the brakes are much higher than the resistance force of the motor. Which would override the available friction of the tires during braking and not regen.

    ABS works by pulsing the brakes. Essentially interrupting the brake force to allow you to regain traction, it does this repeatedly if you keep on the brakes.

    ABS, its not as effective as regen braking aka motor braking (or engine braking in an ICE) in low friction condition. The lower stopping force applied in a consistent manner offers more control.
     
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  13. Joe F

    Joe F Member

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    As a young and invincible (okay, foolish) 18 yr old, I left work at 4 AM only to find a freak ice storm had left a thick layer of ice on everything. Had to use a rubber mallet to break the ice off just to get in the car.

    Nothing like going 5 mph and trying to turn a corner, only to go a few degrees into the turn and jump a curb, with brakes locked. Coworker was scared to death.

    I learned something that day that fortunately have not need since. Hit the brakes, lock the wheels and shift into reverse. It was the only control I had to slow the car down.

    Loved that '59 Rambler Classic (read, tank).
     
  14. Barry

    Barry Member

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    Interesting thread. Based on my experience, spending several days/week in the Colorado Rockies in winter, I find standard regen to be dangerous because it applies too much braking in slick conditions. I always put regen on low when the roads are snow covered.
     
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  15. Yinn

    Yinn Member

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    I think this is right in line with all the posts actually. Using brakes applies more force than high regen, which have more force than low regen.

    As conditions get worse - defined by the reduction in friction/grip of the tires (more icy, downhill, tire quality, etc) the amount of force that the tires can take before breaking loose and losing grip (burnout, skidding, etc) is reduced. That's the same regardless l if you are accelerating or decelerating.

    So as conditions get worse, using less braking force is counterintuitive but more effective. It's more important to apply the force consistently. Going or stopping.
     
  16. goneskiian

    goneskiian Active Member

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    Did standard regen actually cause the tires to break traction?
     
  17. ReddyLeaf

    ReddyLeaf Member

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    I've used that several times as well (make sure to floor it after shifting into reverse to keep the wheels spinning). It works pretty well with a rear-wheel drive car. I haven't tried it with front-wheel drive and I doubt it would work as well due to difficulties with steering control. Hmmm, maybe I'll try it with the Leaf this winter. The funny thing is that everyone I told, claims it cannot be possible. They just cannot comprehend the concept of a sliding car with locked wheels being the same (from the transmission's point of view) as being parked by the side of the road.
     
  18. dhcp

    dhcp Member

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    While in theory, the regen shouldn't have been better than just hitting the brakes, traction tends to come and go as you are rolling while hitting the brakes would only be at that moment. The regen would be constantly trying to apply some drag so as traction would appear the car would get a few moments of slowing even if it just slide after traction went away.
     

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