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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. dsm363

    dsm363 Roadster + Sig Model S

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    You can coast you just can't do it completely by completely lifting your foot off the accelerator.
    When I'm driving around town I have so much range that even if coasting would give me a 10% boost in city range (don't know what actual difference is) I like the one pedal driving with regen. Everyone has their own preferences so if they can add options that would be ideal.
     
  2. brianman

    brianman Burrito Founder

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    In what way is it 'better' (in terms of driver feel) and what do you attribute that to?

    Thanks.
     
  3. dennis

    dennis P85D

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    Subjectively, when you turn into a corner the Karma "takes a set" immediately while the Model S feels like it is understeering, i.e. that you need to give it more steering input. After noticing this I went looking for objective measurements and found that on the skidpad the Model S pulls .86G (Edmunds) and the Karma .91G (Road & Track). By comparison, the 2010 BMW 750i pulls .89G and the Lexus LS460 Sport .84G (Road & Track for both).

    Both the Karma and the Model S have good lateral stiffness and thus corner quite flat with minimal body roll. This gives the feeling of "good handling" that many Model S owners have reported. Like other heavy sedans both cars understeer as you reach their cornering limits.
     
  4. GSP

    GSP Member

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    This is my preference. The Volt is similar.

    Tesla could add a software option that would increase regen above the closed throttle level when the brake light switch closes. Typically this happens before the calipers engage.

    For MS 2.0 I would really like Tesla to add a shift lever with an "L" or "B" position, like the Volt or Prius, instead of the menu option to switch regen from low to high levels. Or, add steering wheel paddle "shifters" like the ELR to adjust regen levels.

    GSP
     
  5. GeekGirls

    GeekGirls Kid in Candy Store

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    I was skeptical initially but after a little less a month of actual experience I'm a complete convert. I love the one-pedal experience (and there are indeed many days when I'm able to drive my entire ~30 mile one way commute without using the brake except when coming to a complete stop.)

    However I think it's a mistake to ask everyone to learn how to drive again. Not everyone is inclined or interested in that level of engagement with a new vehicle. Tesla clearly knows this intellectually as evidenced by the addition of creep and low regen settings. Either one compromises the one-pedal driving philosophy to some extent, and a driver who prefers either would clearly benefit from having regen on brake. These options look like they're intended to be training wheels that come off at some point rather than legitimate alternative modes for efficiently driving the Model S. I think Tesla will find that many drivers are stubborn about changing their habits.
     
  6. jerry33

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

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    No one car can be all things to all people. One of the problems with the Prius is that it tries to imitate an old fashioned car so much that a number of things that could make the car much more efficient are compromised.
     
  7. mknox

    mknox Well-Known Member

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    If I lived in California, I would completely agree with you. Here is someone describing one of my "fears" with gas pedal re-gen on slippery roads.
     
  8. mnx

    mnx 2013 P85

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    You have nothing to be afraid of, the fact that he made it to his destination safely is proof that regen on the accelerator works just fine. (even with 21" summer tires on snow covered roads!)

     
  9. Jaff

    Jaff Active Member

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    Mike, in the short time that we have had our Model S, when driving in snowy / icy conditions, I have not found any sort of "regen induced slippage"...in fact, driving get my Roadster through the past two winters, I have not encountered this even though the Roadster 's regen is far stronger than the Model S regen...My opinion is that this chap was experiencing these difficulties due to the inadequacies of the summer performance tires in the snow.

     
  10. mknox

    mknox Well-Known Member

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    I'm glad to hear that.

    About 6 or 7 years ago, I was driving a GMC Envoy. I had it in 2WD (driving the rear wheels) with cruise on. As I was coming down a steep hill on Hwy 9 outside of Orangeville, the vehicle downshifted (which it did sometimes to slow down and maintain the speed setpoint on downgrades) and due to black ice that I was unaware of, the vehicle spun out when the rear tires lost traction. I spun 360 degrees into the oncoming lanes (fortunately no cars coming) and when the vehicle hit dry pavement, I peeled two tires right off the rims and went backwards into the ditch. To this day, I am amazed it didn't roll (and am thankful there was no oncoming traffic). That car had traction control too. This is why I get concerned about aggressive re-gen on the rear wheels in slippery conditions. I know the Model S is no top-heavy SUV, but that experience has made me very sensitive to this issue.

    I still don't understand why people are so aggressively against the idea of making an option to move re-gen to the brake pedal (activated when the brake light switch comes on) for those who want to coast when you take your foot off the accelerator and rely on the brake pedal for stopping. Those who like one pedal driving would leave it as is. I would likely leave it in standard mode all spring, summer and fall but would flip it over in the winter for these reasons.
     
  11. jerry33

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

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    I'm not aggressively against it. I just understand how it would have to be implemented. It would take a boatload full of R&D dollars to get right and would add complexity and raise the car's price. Right now Tesla just buys off the shelf brakes and installs them--simple, cheap, foolproof. If they did regen-on-the-brake-pedal they would have to design their own brakes from the ground up plus all the controlling systems. There is just no way to make regen-on-the-brake-pedal simple--it's very difficult to get right. Toyota has been working on this for over sixteen years and some people would say they haven't got it right yet. (That's not my opinion BTW).
     
  12. dennis

    dennis P85D

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    Well Fisker got it right on the first try, and so apparently did Chevy (Volt) and Nissan (Leaf). While there have been complaints about other aspects of the Karma on the FiskerBuzz forum, I can't remember a single one about the brakes or their integration with regen.

    I disagree that Tesla would have to design their own braking system from the ground up. The friction brakes remain the same, it is just a question of when they get actuated. That is a function of the controller software that typically comes from Bosch who pioneered ABS systems. So my guess is that the manufacturers like Fisker who use regen for initial braking provide additional requirements/specifications to their provider of the braking system software, as opposed to having to do everything themselves.
     
  13. jhs_7645

    jhs_7645 VIN: #3305

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    I'm not sure people are as aggressively against it as you think. For the most part I think people who currently own and drive the car are trying to assuage your fears that something is wrong/dangerous with the car the way it is currently designed. You really shouldn't worry about the safety, behavior and performance of the way it is currently implemented. This reminds me of the pano sunshade. There was an uproar for months on the forums when people got wind of the fact that there might not be a sunshade. Then, when people actually got the cars, and drove them in Florida on sunny days, everybody agreed.. no sun shade necessary. I would encourage you to just leave the topic alone for a while and wait until you get your car, and trust the people who have their cars that this is a non-issue.
     
  14. Zextraterrestrial

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    I'd be a little pissed if regen was on the brakes and love it as is. It is much nicer to be able to slow a bit without moving your foot over or flashing your brake lights at people.

    The regen doesn't peak when you push the brake because of physics.
    someone please correct me if I'm wrong
     
  15. dennis

    dennis P85D

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    I think you are missing the point that cars like the Fisker Karma have regen on BOTH the accelerator and the brake pedal. If you lift your foot from the accelerator, you get some regen (you can select from 3 levels). Then when you step on the brake pedal the first .25G of deceleration is accomplished through regen, peaking at 90kW. If you need to decelerate faster than that, the Brembo friction brakes are actuated. It is all seamless, and maximizes regeneration without having to fret over whether or not to use the brake pedal.
     
  16. mknox

    mknox Well-Known Member

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    I think that's a fair comment as I don't have the car yet, and with receiving it in the spring, I'll have a whole summer driving season to get used to it. Having said that, I still think an OPTION to switch the re-gen mode wouldn't take anything away from those who like it the way it is, and appease those who would like it to work diffidently.

    - - - Updated - - -

    I don't think it has to be that complicated. Just an OPTIONAL mode that turns re-gen off on the accelerator (so that you coast when you lift your foot), and then switch in some reduced level of re-gen when the brake pedal is squeezed just enough to turn the brake lights on. Squeeze a little harder and the regular friction brakes kick in. Something that could prevent a sudden loss of traction is worth the time it would take to implement this in software, IMHO.
     
  17. Zextraterrestrial

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    #57 Zextraterrestrial, Jan 28, 2013
    Last edited: Jan 28, 2013

    my point...
    Does The Fisker have an AC induction motor like the S? or are there some magnets in it?

    2 motors on the Fisker? maybe that is the difference.
    Until someone has an answer, I think it is the physics of the motor fields (someone educate us please? where are the ME/EE's)
     
  18. ElSupreme

    ElSupreme Model S 03182

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    There is NO reduction of regen when you press the brake pedal in the Tesla. I think you are thinking that Fisker/GM/Nissan have somehow figured out a way to increase regen. I can see some arguments for putting regen on a brake pedal, but most of those revolve around mimicking the behavior of current automatic transmission ICEs. I would argue it is much easier to maximize regen with one pedal because you won't accidentally use friction brakes while slowing down. Again I point out the simplicity of having one pedal work one system.

    And we need to stop with 'Tesla should make this user selectable' on everything. What if I wanted the brake pedal to work the as the accelerator, and the accelerator to work as the brakes? In reality people HATE making all of these choices. I know we all want the car to work the way we want it but give it some time.
     
  19. jkirkebo

    jkirkebo Model S P85+ VIN 14420 EU

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    I complain about the regen/braking on the Leaf. There is too little regen on the accelerator (and I always drive in eco) so the brake pedal must often be used. But there is no way at all to detect where regen ends and mechanical braking begins. Thus I often waste energy on the braking.

    If there must be regen on the brake pedal there should be a defined point one could easily detect where mechanical braking begins. But my opinion is that the current Tesla system is much, much better as you always know which type of braking you do.

    I often have no regen at all now in the Leaf, because of the cold battery. This has not caused any problems at all, I see this as a non-issue. I quickly detect the amount of regen available and adjust the driving automatically without thinking of it.
     
  20. Alpha

    Alpha Member

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    If regen could be made exceptionally strong (like with multiple motors on the model X, or even one motor on each wheel) then it might make more sense to have regen integrated more into the brake pedal (and have the brake lights go on, etc. to warn people behind you of your sudden deceleration.)
    I agree that the average person is overwhelmed with too many choices, but a lot of geeks, engineers and scientists love to tweak things endlessly...
    I think there are a lot of Model S owners who fit in that category ;)
     

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