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Regen discourages coming to a full stop

Discussion in 'Model S: Driving Dynamics' started by holstein13, Jan 26, 2014.

  1. holstein13

    holstein13 Member

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    While I love the regenerative braking on the Model S, I really wish it would take the car to a complete stop. I find myself slowing down long before a red light and hoping it will turn green before I have to put my foot on the brake. At stop signs, I have no desire to come to a full stop (although I still do).

    Does anyone else feel the same way or is it just my OCD?
     
  2. jerry33

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

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    I try to time the stoplights so that I don't have to fully stop. In Texas only a few stop at stop signs or before exiting a parking lot regardless of vehicle type, so it's a non-issue :)
     
  3. wiztecy

    wiztecy Active Member

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    #3 wiztecy, Jan 26, 2014
    Last edited: Jan 26, 2014
    Its NOT the car, its the DRIVER!

    I love my regen and don't avoid coming to full stops at stop signs. If you don't want to stop you won't put the effort in. You need to identify your bad habits and see the full the consequences of them. Unfortunately these consequences will directly affect the lives of other people who do want to stop and be aware of others. Sorry, but I'm very firm on people who cross the line on roads, roll through stop signs, and are oblivious of others who're on the road. I see that 95% of people on the road have 0 consideration for others and put my life at risk due to their lazyness and unawareness.

    Its one thing being in the Great Plains where you can see miles at a 4 way stop, but still then, the road and heat can play tricks on you and you should always stop.

    ALWAYS stop at stop signs. They're there for a reason and I'm paying tax dollars for them to ensure MY safety.
     
  4. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    Hypermilers use a set of techniques called "driving wihout brakes" to avoid any braking, including regen because deliberately shedding momentum is inefficient. What you are doing is a kind of smart braking where you're trying to make the best of a bad situation and retain as much momemntum as possible, and with no-regen-braking you don't want to hit your brakes and waste all the scrubbed momentum.

    When you consider that the more speed you can keep the more speed people behind you can keep, no it's not a problem. However, note that simply by regen down to a low speed, final braking to a dead stop won't work the brakes very hard.

    Since this thread has veered into hypermiling territory, let me throw in a couple of key tips (Golden Rules) for safety and efficiency:
    1) Anticipatory focus: see everything, as soon as possible by focusing ahead and ancitipating potential maneuvers.
    2) Buffering: leave plenty of space (actually time) to the vehicle in front; 2 seconds is a minimum, 4 seconds is now recommended, but the more the merrier
    Do those two well and you'll be braking (and regening) less without even trying just because it gives you more space and time, which leads to action instead of reaction, with better decision-making and fewer sharl maneuvers.
    (Newton's Third Law of Driving Too Close: every action has an excessive reaction.)
     
  5. Larry Chanin

    Larry Chanin Model S Perf Sig 1055

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    It was my shocking observation after moving down to South Florida that nobody stops for stop signs, regardless of whether they are driving gasoline vehicles or electric vehicles. :wink:

    By the way, if you are interested in joining our Florida Tesla club, please click on the link in my signature.

    Larry
     
  6. Vger

    Vger Active Member

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    I believe the reason that regen cannot get the car all the way to a stop is simple physics. The kinetic energy of the car (which regen braking is harvesting) is computed as:

    Ek = m * v**2

    So kinetic energy is proportional to the square of velocity. That means it decays non-linearly as the car slows down. At a walking pace, the car does not have enough kinetic energy to drive the drivetrain running as a generator, and the car keeps rolling.

    Better physical scientists or engineers than me (I am a neuroscientist by training) will, no doubt, refine my explanation!
     
  7. ckessel

    ckessel Active Member

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    *shrug*, it's no different than how I treated slowing down in 1st gear in a manual.
     
  8. djp

    djp Roadster 2.0 VIN939

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    Another way to look at it is the regen forces you to take your foot off the accelerator and hold the brake at a stop, which is the safe thing to do.

    Covering the accelerator at a stop is asking for trouble if your foot slips or your car is bumped from behind.
     
  9. Doug_G

    Doug_G Lead Moderator

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    That is correct as far as it goes, but it neglects other possibilities. Tesla could actually apply just a little "reverse thrust" until the car comes to a complete stop.

    Nevertheless, I agree that it's smart to have your foot on the brake pedal while stopped.
     
  10. brianman

    brianman Burrito Founder

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    I think you're misreading his post and overreacting as a consequence. Or, at the very least, I'm interpreting his post radically differently than you apparently are.
     
  11. stopcrazypp

    stopcrazypp Well-Known Member

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    I think that's probably what the i3 does, as it can come to a complete stop without stepping on the brakes.
     
  12. physicsfita

    physicsfita Member

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    The force associated with the regen should be proportional to the speed of the car -- this means that the rate at which the car's speed is decreasing is proportional to the speed of the car itself. This works out to an exponential decay of the speed of the car -- approaching zero but never getting there.
     
  13. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Right. In addition, the MS software seems to cut regen completely around 5mph.
     
  14. brianman

    brianman Burrito Founder

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    Assuming of course there's zero friction on the road...
     
  15. physicsfita

    physicsfita Member

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    There better be static friction, or the tires won't roll. :tongue:

    It was getting late, and I didn't want to build a full Mathematica model to factor in rolling friction and air resistance -- sounds like a good homework problem to assign, though. Hmmm.... :rolleyes:
     
  16. jbadger

    jbadger Roadster #506

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    I know the Model S regen breaking isn't as harsh as the Roadsters, but I can and often do time the regen breaks to bring me to a complete or 99% stop. As others have stated, it's a best driver practice to always cover/press the break when stopped to prevent accidents.

    i do wish the Model S had an even stronger regen option. In this way, the Roadster is much better in my opinion.
     
  17. holstein13

    holstein13 Member

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    I always come to a complete stop at stop signs and I never run red lights. Why the rant? and what makes you think I don't?
     
  18. NigelM

    NigelM Recovering Member

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    I don't use creep and I do come to a complete stop with regen braking (eventually). You just have to gauge the distance correctly.
     
  19. Lawsteve

    Lawsteve MCATDT

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    Here we are allowed to make a right turn on a red light, but technically are required to come to a full stop first. Most people roll through that right turn. The practice has diminished substantially because of automated red light cameras that will issue tickets by mail ($158.00 - ask my wife!) if your car is caught rolling around a corner. The cameras are not at all intersections, thus you can roll through as long as you know which intersections are the camera traps.

    I always stop at stop signs, as too many other people don't! When I'm the first person at a red light, I also pause before entering the intersection, as there also are a lot of people who run the red lights (less now -see camera discussion above).

    in light of the above, I'm pretty much limited to timing the regen when I am approaching a red light. I'm slowly getting pretty good at that.
     
  20. N4HHE

    N4HHE Member

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    I think you did an excellent job explaining it, not that many will understand.

    Another way to look at it is that near 0 RPM the motor can not regen a high enough voltage to put anything back in the battery. So near the end where it currently does almost nothing the alternative would be to reverse the torque on the motor as the only way to get braking out of it. And that would be the opposite of regeneration.
     

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