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Do brake lights always turn on with regen? (incl gap to other cars)

Discussion in 'Model S: Interior & Exterior' started by contaygious, Sep 13, 2012.

  1. contaygious

    contaygious Active Member

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    Sorry couldn't find a recent answer. Do they always come on or just with big speed changes? Will it appear as if we are super brake pedal happy?:confused:
     
  2. Doug_G

    Doug_G Lead Moderator

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    They turn on when you reach a certain deceleration level (roughly half), and they also turn on immediately if you lift off the pedal quickly.

    If you just lift a little they do not turn on.
     
  3. smorgasbord

    smorgasbord Active Member

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    First, I wonder if the algorithm is the same as Roadster's.

    Second, new Tesla drivers often look like they don't know what they want to do. The typical ICE style of lifting off the accelerator completely to coast is a hard habit to break, and on Roadster it causes super fast acceleration followed by brake lights. Even just in traffic on the freeway, some Roadster drivers will appear crazed.

    With some practice, you learn not to lift off the accelerator completely. You learn to find that spot where the power output is zero, which is actual coasting. A side benefit of this is better efficiency.
     
  4. Raffy.Roma

    Raffy.Roma Active Member

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    Nice....this system is really smart expecially when you think to the reduction of brake pads consumption.
     
  5. contaygious

    contaygious Active Member

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    Ok thanks! I saw a test drive video a while back where the rep said it always comes in so wanted to double check. I'm one of those tip tronic drivers that usually downshifts to slow down instead if braking,
     
  6. Todd Burch

    Todd Burch Electron Pilot

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    My thinking was that any time the brake pedal's pressed, the lights come on (as in a conventional ICE vehicle). On the power pedal side, it's all accelerometer based. Is that correct?
     
  7. Doug_G

    Doug_G Lead Moderator

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    It might be an accelerometer, but more likely they're using power from the motor (or a corresponding control system variable) to determine deceleration.


    By the way when the creep starts to kick in the brake light goes out. If you want it to stay on for the last few feet of deceleration you should press the brake.
     
  8. Todd Burch

    Todd Burch Electron Pilot

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    I've heard a number of times from different Tesla employees that it uses an accelerometer for this...but as we know, that doesn't necessarily mean it's true.
     
  9. jerry33

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

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    We know that it's based on "braking force" and not just when you touch the brake pedal because it comes on when you use regenerative braking hard enough. I though that there was no question that it was using an accelerometer because that's what's been said for months. I suppose it could be done by monitoring the rate of deceleration though the speedometer mechanism but that seems complex compared to an accelerometer and more prone to problems.
     
  10. cinergi

    cinergi Active Member

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    It has to be smarter than just accelerometer / deceleration: Imagine a steep downhill where there's significant regen required to keep the car at a constant speed. I'm pretty sure the brake lights are on in this condition.
     
  11. Todd Burch

    Todd Burch Electron Pilot

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    It's certainly feasible to set up that *either* deceleration above some threshold *or* use of the brake pedal lights the brake lights.

    In that case, the car is pitched down and even though its speed may be constant, the gravity vector has enough forward component that the accelerometer would register an apparent braking force...lighting the brake lights.
     
  12. spatterso911

    spatterso911 MSP#7577 **--** MX#1891

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    Heard the same thing.
     
  13. cinergi

    cinergi Active Member

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    Curious to know if an accelerometer measures that? I figured it only would "see" vector changes. Still, how would it know the difference between 1 MPH downhill and 30 MPH downhill (the former would not light up the brakes)? I'm still convinced it's more complex than just an accelerometer (this is based on my observations in my Roadster; obviously may be different in Model S, but probably MORE advanced).
     
  14. Todd Burch

    Todd Burch Electron Pilot

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    Standing still on the earth we're at 1G of acceleration downward...the necessary centripetal acceleration to continue moving in an (approximate) circle as the earth rotates. So while we are apparently not accelerating from our own point of view, if viewed from space we in fact are. Accelerometers will measure that centripetal acceleration. (By the way, these are the kinds of initial thoughts that spurred Einstein's Theory of Relativity).

    You're absolutely correct. Viewed from space, our vector is continuously changing in order to keep us on the surface of the earth, moving in an approximate circle.

    How do you know it doesn't come on at 1 MPH downhill? Have you tried this in the Model S? If I'm in a conventional car going down a steep hill at 1 MPH (and remaining there) I must be on the brakes to prevent my car from speeding up.

    You could very well be correct that it's more advanced...I guess that's what this thread is about!
     
  15. Timothy

    Timothy Driving on Sunshine

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    The way to get a feel for when the stop lights come on is to drive at night and practice decelerating at different rates. You can see the red glow reflection from the wind wing in your rear view mirror when the stop lights come on , and will learn how quickly you can decelerate without activating the stop lights. You can't tell this in the daytime, unfortunately, as the red stop light reflection isn't bright enough. I wish there were a light on the console so you could tell when the stop lights come on in the daytime.

    Kind of like double clutching when you downshift a non syncro ICE. A skill you learn with practice. At least this one doesn't grind the gears!
     
  16. cinergi

    cinergi Active Member

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    Not in the Model S -- just in the Roadster. And the Roadster's definitely not just measuring deceleration. It would be too inaccurate to do so. I assume (yes, I know -- assume) the Model S is at least as intelligent, if not more. Which means it's more than just the accelerometer. I think it should be enough to just measure regen capture in relation to your current speed.

    I definitely take the "they said it has an accelerometer" with a grain of salt because a lot of long-time, well-known, respectable Tesla employees STILL say stuff like "This box up front in the Roadster is a 400 -> 12V converter" when it's in fact a controller (at least on the newer Roadsters).

    Interesting way to think about it. So, on a horizontal surface, it would be indicated/measured as 1G (standard gravitational pull) "straight down" (towards the center of the earth)? In a parked car on a downward incline, the vector would be down-and-forward relative to the car. This would be the same for a car moving, but holding speed via regen. A car that was freely accelerating downward would have ... a vector that's perpendicular to the car? Do I have all this right? haha my brain hurts. :smile: I can at least now see the vector's still useful in my downward holding-speed regen scenario.
     
  17. aviators99

    aviators99 Model S - R140

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    IMO, its actual performance is consistent with a simple accelerometer, as Tesla has stated in several interviews.
     
  18. strider

    strider Active Member

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    Though note for some European countries there is a rule that says the brake lights may only be activated by the brake pedal so in those places the brake light on regen is disabled. You can search around the Roadster forum for more info.
     
  19. jkirkebo

    jkirkebo Model S P85+ VIN 14420 EU

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    Why would you want them to be on ? In an ICE car I just downshift to the appropriate gear for the downhill, and the brake lights never come on unless it is so steep that I have to brake occasionally. If I have to, I brake hard and for a short time so the brakes can cool off in between. People who have their brake lights on all the time coming down a mountain pass come off like driving amateurs and their brakes end up smoking hot and sometimes failing.

    I certainly don't want my brake lights being on when keeping constant speed on a steep downhill.
     
  20. Doug_G

    Doug_G Lead Moderator

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    The Roadster regen is significantly stronger than downshifting an ICE. You'd have cars up your ass without the brake lights.
     

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