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Why isn't regen integrated with the brake pedal?

Discussion in 'Model S: Driving Dynamics' started by dennis, Jan 24, 2013.

  1. dennis

    dennis P85D

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    I think you don't appreciate how clever the Fisker regen implementation is. It wouldn't be safe to generate .25G of deceleration through regen just by lifting off the accelerator, as it would be too abrupt and your brake lights wouldn't be on to warn the traffic behind you that you were slowing down that much. But while the Karma does provide regen while lifting off the accelerator, it generates additional energy by using regen (up to 90kW, as shown on an instantaneous digital display) to provide the first .25G of deceleration when the brake pedal (and brake lights) are actuated. This has nothing to do with mimicking ICE behavior, it is just a clever way to maximize regen without compromising safety or forcing a new driving style.

    I never suggested that the Model S be changed. My OP was seeking to understand why it behaved differently. Unfortunately, I still don't have an answer to that, although a couple of posters have suggested it may have to do with a difference in electric motor technology.
     
  2. dsm363

    dsm363 Roadster + Sig Model S

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    I agree with the suggestion that people who have questions about it wait until they get their car and see how they like it. I can't compare it to a Prius or Fisker having never driven them but I like how Tesla has implemented it. If they can easily and cheaply make regen on brake an option then that would be great. I wonder how that would effect range and their EPA numbers as turning the option on would change things (possibly increase or decrease range depending on how the cycle is done).
     
  3. Doug_G

    Doug_G Lead Moderator

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    This. With Tesla's method, you can easily get 100% regen with no thought whatsoever. Also it's just an easier way to drive. IMHO of course.
     
  4. jomo25

    jomo25 Active Member

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    Not this. Sigh. What should be available is the option to do either. The Volt does. Why couldn't the S?
     
  5. dennis

    dennis P85D

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    But with the addition of brake regen I can get 150% (90kW vs. 60 kW), also with no thought whatsoever.
     
  6. GeekGirls

    GeekGirls Kid in Candy Store

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    As others have pointed out, some people love options and others hate them. I tend to avoid them in designs not solely because of the overhead associated with validating every possible combination, but also the complexity of trying to describe how to do anything with a heavily customizable product ("to drive efficiently do A except when option B is enabled, then do C, unless you also have option D or either E or F, but not both ...") My rule of thumb? Avoid options wherever possible. Far too often it's a matter of abdicating responsibility for figuring out what would be a good design by letting your customers choose among sub-optimal alternatives.
     
  7. Jason S

    Jason S Model S Sig Perf (P85)

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    How? Exactly how do you get more regen by putting some of it on the brake pedal?

    They left none on the plate. It is ALL on the one pedal. You are talking about a different car now, one that somehow has greater regen available than the Model S. And you've designed the system differently too.

    What is it about the brake pedal that increases the amount of regen available?
     
  8. Doug_G

    Doug_G Lead Moderator

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    Uh, no, you get 60 kW of regen and 30 kW of wasted energy in the form of hot brakes.
     
  9. jomo25

    jomo25 Active Member

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    You can't plan or design for every option. However, you can and should strongly consider planning and designing options for realistic use cases, esp. if you are trying to build a product with wide appeal.

    I will get used to and quite likely love the one pedal driving method like the S has. (As it is, I drive in L most of the time in my Volt, which essentially does the same). But I promise you my wife, who has never driven a stick, and can't stand the L mode on the Volt will not like, and will not ever like, the S implementation. It just doesn't feel natural too her. And she won't drive it enough to get used to it. But she will drive the car occasionally (out of necessity if for no other reason). Now, she can just set her profile to "low" regen, but then she has to sacrifice efficiency to get the feel she likes. If the option existed as it does on the Volt, she can get the feel she likes and still maintain a respectable level of efficiency.

    OK, this isn't a "realistic" option. Using this argument is like the people who are against gay marriage because "well if you allow gay marriage, then why shouldn't we just allow people to marry animals".
     
  10. dennis

    dennis P85D

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    Wrong. I am talking about my Karma, where the brake pedal activates additional regen, and I am viewing the instantaneous display of regen energy increasing from about 40kW before I applied the brakes to 90kW. Only after exceeding .25G of deceleration are the friction brakes activated. So no wasted energy.
    I must have explained this 4 or 5 times in this thread. Is this really hard to understand or am I that bad at presenting information? :frown:
     
  11. ggr

    ggr Roadster R80 537, SigS P85 29, M3P 80k

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    I've been ignoring this thread, and just rejoined. I just got the .42 update, and one of the things is it seems to make the regen slightly stronger. Anyway, my 2c worth is, the S could, but why should it? I think one foot driving is just pretty darn good. I like it the way it is.
     
  12. brianman

    brianman Burrito Founder

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    Just for argument's sake...

    Would you be willing to pay for the R&D cost of that "optional mode" by paying for the option to have setting? Say it cost you $250. Would it be worth it to you?

    I think the reason some are arguing strongly against the option is that they feel it's a waste of Tesla resources, and adds to the cost of vehicle design and production.
     
  13. dennis

    dennis P85D

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    I'd much rather have Tesla spend their R&D $$ on door handles that auto-present. :rolleyes:
     
  14. brianman

    brianman Burrito Founder

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    Well at least we can agree on that.

    Though mine auto-present fine (so far?).
     
  15. ChrisgG

    ChrisgG Member

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    $250 would be a nobrainer, yes i would pay that. Unfortunately it probably would more be like $2'500.

    The Spartan way of building the Model S might be a necessary, and do we really need this? no we don't, but it would have been better.
     
  16. jerry33

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

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    More complex and more failure prone, yes. Better, not so much.
     
  17. ChrisgG

    ChrisgG Member

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    If you want to go that route please get rid of the door andles, the frameless door, the touchscreen, electric windows, all those drive safe features and so on. Because less is more.... not so much.
     
  18. jomo25

    jomo25 Active Member

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    The auto-presenting electronic handles are an obvious one. But I see it more valuable than different steering modes and yet "R&D was spent, and we're all paying a premium for" that option.
     
  19. Doug_G

    Doug_G Lead Moderator

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    I'm not in the habit of watching screens while braking to determine if I'm doing it optimally. Something about it being, I dunno, maybe dangerous?
     
  20. jomo25

    jomo25 Active Member

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    As if people arent already looking at the dashboard's energy use line to know where coasting is.

    Having different deceleration rates when regen is limited, now that's what I call dangerous.
     

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