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Why regenerative braking belongs on the brake pedal

Discussion in 'Model 3' started by JeffC, May 25, 2016.

  1. jerry505

    jerry505 Member

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    For less regenerative braking lift foot more slowly off throttle.
     
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  2. Canuck

    Canuck Well-Known Member

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    I bet when you get a Tesla you will be off low regen after less than a month of owning the vehicle. Mark my words on that one.
     
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  3. JeffC

    JeffC Member

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    #83 JeffC, May 25, 2016
    Last edited: May 25, 2016
    I understand your points. My point is that regen belongs with the friction brakes for ergonomic and safety reasons.

    Agree it would be hard to get oversteer from regen, but it could happen in low friction situations like wet roads. I applaud you for taking the time to learn about performance driving and to exercise your cars and skills regularly. I wish more people did that. They would be safer drivers if they did. I need to get back on the track a lot more too.

    The problem is what happens when people who don't have that kind of training, skills and knowledge get into situations they're not prepared to handle. My point is that heavy regen off throttle makes that more likely for the less skilled drivers.
     
  4. JeffC

    JeffC Member

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    Understood. The same maximum regen can be put on the brake pedal instead of the throttle. Basically it would be a software change.

    It's a different way of organizing the same regen: integrate it with the brake pedal instead of the throttle.
     
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  5. JeffC

    JeffC Member

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    #85 JeffC, May 25, 2016
    Last edited: May 25, 2016
    Most EVs and hybrids have regen on the brake pedal, not the throttle.

    With regen integrated with the brake pedal, to get regen, you use the brake pedal. The initial part of the braking is performed by regen, up through maximum regen. The friction brakes do the rest of the work beyond that. All braking, both regen and friction, is on the brake pedal.

    I explained in my essay linked in the first post some of the reasons why that's desirable.
     
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  6. deonb

    deonb Active Member

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    A lot of people on here comes from the Roadster performance-enthusiast world, and many additional members are performance and/or racing trained drivers. We even have professional racing drivers than own Teslas popping in every now and again.

    There are enough people on here that know how to deliberately oversteer a car to be able to report on it. I've never heard a report about the regen being too powerful for the TC. And if you don't trust Tesla's TC you should really not be driving a Tesla even in a straight line.

    Keep in mind that the electric drive train & instant torque is the reason that Tesla can get the TC to perform so well, much much better than you can ever get out of an ICE TC. And because of that, it allows to to take more liberty with the regen.

    Here is an interesting read (albeit a bit old) from one of the guys that worked specifically on the Roadster's regen traction control:
    The Spin Stops Here | Tesla Motors

    Telling: "And, perhaps what is most impressive, the TC’s ability to maintain traction allows even expert drivers to achieve higher performance than they are otherwise capable."

    You're going to depend on Tesla's TC around every corner you take. If you can't live with that, don't buy a Tesla.


    I have ready your essay, which is why I'm now pushing for credentials and/or studies & surveys you've done from people who actually have experience with it.
     
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  7. JeffC

    JeffC Member

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    #87 JeffC, May 25, 2016
    Last edited: May 25, 2016
    Hi Deon, I fully expect Tesla's traction control to be very capable, especially since electric motors can respond so much more quickly and accurately than combustion engines and transmissions. That very responsive mechanical platform really amplifies and simplifies the effect of good software applied to the task.* The problem is what happens when the recoverable limits of the tires are exceeded and how it's possible to get there.

    My essay is a position piece explaining reasons for the position. It's not an accident inquiry, etc., though I agree it would be nice to have some concrete examples.

    * A general philosophy of Tesla seems to be to have very good but relatively simple mechanical engineering, then apply software in very smart ways. It's a great combination.
     
  8. deonb

    deonb Active Member

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    As far as the "possible to get there":

    If I understand you correctly, you are effectively saying that the unskilled driver can move their foot rapidly off the accelerator around a slippery corner in order to slow the car down, and as such induce a regen-based oversteer spinout.

    Well, without accelerator-based regen, that same unskilled driver would have just had their foot on the break trying to enact a similar slowdown, and would cause a similar regen-based oversteed spinout. So what's the difference?
     
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  9. JeffC

    JeffC Member

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    #89 JeffC, May 25, 2016
    Last edited: May 25, 2016
    I've used relatively heavy regen on all of my previous and current EVs, such as when slowing down for a stop light or coming off a highway offramp. They all had/have switches or positions for more levels of regen on the shift levers.

    But for other braking situations such as driving in traffic, I prefer the regen to be on the brake pedal. To slow down, I use the brake pedal. I get maximum regen by using the brake pedal. If I press the brake pedal harder, or to come to a complete stop, the friction brakes get used a little. For a panic stop, the regen would go to maximum, and the friction brakes would get a lot more work. All is integrated onto the brake pedal. I find it convenient to have all the braking on the brake pedal.
     
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  10. JeffC

    JeffC Member

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    Yes, that's exactly what I'm saying.

    The difference is that they might get into oversteer due to the regen, where they wouldn't without the regen. In other words the regen on throttle lift might brake (heavily) when they didn't want to brake, but simply wanted to slow down (less) by lifting off the throttle. Regen on the throttle makes the effect of lift throttle oversteer worse. It magnifies the problem. It's like adding heavy braking when they didn't really intend to.

    It doesn't need to be a slippery road either, though it could make it more likely.
     
  11. newtman

    newtman Member

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    Oh you've spoken with a significant number of engineers within Tesla?
     
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  12. deonb

    deonb Active Member

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    Ahh, but here is where there is a huge discrepancy which you can only really understand once you have a Model S. The act of lifting your foot of the throttle on a Model S is not to "slow down a little". It's to: "put your passengers up against their seatbelts" and is very uncomfortable. So you stop doing that. Very, very quickly.

    If you want to slow down a little you know to ease of the accelerator a little. It becomes second nature. It really, really does. You don't have to be trained for that - my wife is definitely not trained, to put it mildly... and even she got it perfectly right after about 2 weeks - now she's better at it than in any previous car.

    Sure, in an emergency situation you may lose your cool and lift your foot of completely, but then I hold it back up to you that in an emergency situation you're equally likely to lose your cool and press the brake.
     
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  13. GoTslaGo

    GoTslaGo Learning Member

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    To quote the essay:

    "...Most non-racing-trained drivers don't know how to react to trailing throttle oversteer:..."

    Maybe you should talk to your Tesla engineer friend not about a radical redesign, but a Tesla Performance Driving school (like BMW). Training and experience is what matters.

    Coming from manual transmissions and years of driving in inclement weather, regen on the throttle is the best. Much better and faster control than shifting feet.
     
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  14. Jason S

    Jason S Model S Sig Perf (P85)

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    Pretty sure you can do that with summer tires on icy roads (maybe only on RWD Model S with standard regen tho -- no experience with the D models to know if different). Not saying that's something a rational person should engineer around tho.
     
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  15. FlatSix911

    FlatSix911 Porsche 918 Hybrid

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    #95 FlatSix911, May 26, 2016
    Last edited: May 26, 2016
    Interesting reading. As a track instructor with rear engine cars, I agree with most of your points regarding regen.
    One recommendation is to add some diagrams to help illustrate the concept of over and understeer to your essay.
     
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  16. ZachShahan

    ZachShahan Active Member

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    There's plenty here, but I'll just add that your argument "it's better because of driver psychology" includes quite limited assumptions about the topic.

    The BMW i3 has the strongest regen on the market (I think) specifically because its ActiveE drivers consistently asked for stronger regen. one-pedal driving is a simplified, convenient improvement to what increasingly seems like a tedious routine that has been slow to improve in fundamental ways. People mostly love it ... *once* they get used to it. My mom & sister got used to it by the end of a couple of test drives and quickly loved it. Yes, the initial response is typically, "Oh, this is different, I have to get used to it." But the majority of people seem to develop a strong preference for it once they get used to it.

    To ignore the continuous, significant benefits here for the driver (which is obviously related to matters of psychology) is to miss more than half the story, imho. There are obviously also going to be occasional safety benefits to the braking kicking in as soon as you take your foot off the pedal.

    Driving the 500e, LEAF, etc., was a real disappointment after driving a Tesla or BMW i3 due to the loss of that strong regen braking (not to mention acceleration ;) ).

    (And FYI: BMW's traction control on the i3 is superb and supposedly makes it impossible to do donuts.)
     
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  17. ZachShahan

    ZachShahan Active Member

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    OK, and one more thing...

    You're talking about very rare examples where it might be safer to have more typical braking, but if we're going to talk about such rare cases, we could also bring up the possibility of someone's foot slipping when they go to use the brake (which they wouldn't have to do with Tesla's strong regen), getting a cramp from a lot of driving where you are switching back & forth between the accelerator and brake pedal (and that resulting in an accident), and I'm sure other such rare examples that would be comparable to Tesla's combination of tech resulting in an accident....

    In other words, no offense at all and hope that this isn't rejected just because it goes against your thesis, but I think you've simply too narrowly evaluated the pros & cons of Tesla's braking system based on a particular avenue of the tech that you are interested in and knowledgeable about as well as assumptions about the full net benefits of strong regen like the Model S & i3 use.

    (All of that said, I have nothing again automakers offering various regen settings -- thought that was a great thing in the e-Up! & e-Golf -- and that could actually help more drivers to learn how to respond to a greater variety of driving challenges and be more attentive to how their car is working.)
     
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  18. jerry33

    jerry33 (S85-3/2/13 traded in) X LR: F2611##-3/27/20

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    I wonder if those engineers have ever driven a Tesla. It's so much better than regen on the brakes. (Drove a car with regen on the brakes for 150,000 miles and it never did stop accelerating when braking over pavement irregularities. Just about unusable on washboard surfaces. Regen on the brakes is such a bad idea it's a wonder anyone did it.)
     
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  19. garsh

    garsh Re Member

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    I call BS on this. The Leaf never gets close to 80kW regen. The most I've seen is under 30kW. Furthermore, the Leaf does blended braking, so it's pretty difficult to not use the friction brakes while slowing down. I was surprised by how worn my brake pads are.

    From the article:
    Go spend some time at mynissanleaf.com. You'll see that the "trees" display is universally ridiculed as a gimmick. It doesn't even correspond to efficiency - it's more like the efficiency difference between the Leaf and an ICE driven in the same manner. So you end up growing more trees by using jackrabbit starts & stops or getting stuck in a traffic jam instead of actually driving efficiently.
     
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  20. bhzmark

    bhzmark Active Member

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    #100 bhzmark, May 26, 2016
    Last edited: May 26, 2016
    Dude, take a deep breath. Buy your tesla. And then come back here and tell us what you think.

    I was in exactly in your position, making the same and more, and I'd like to think better, arguments. I was even emailing with jerome guillen about it (I cant believe he was so polite to me).

    The brake pedal

    Model S regenerative braking with brake pedal

    Model S and coasting, increasing the comfort for passengers

    P85D - Electric Mechanical Braking System



    And then I bought and drove many miles in my tesla and realized I was wrong. You likely will too.
     
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