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Is low regen setting best for highway cruising?

Discussion in 'Model S: Driving Dynamics' started by scottm, Mar 8, 2015.

  1. scottm

    scottm Active Member

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    On long highway trips with many open miles and slight undulations and small hills, enough to be dipping into regen green occasionally, would it be best to have regen setting on low to slow down less on declines and use the momentum instead to help up the inclines, rather than pocketing the extra juice of stronger regen?

    Anybody done that taken the same trip several times with the two different settings to compare achieved distance and capacity consumed?

    I guess having cruise control locked on would be a good constant for this "study".
     
  2. CHG-ON

    CHG-ON Still in love after all these miles

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    I have read a few posts saying it is better to use low on long highway cruises. My experience has been that it is much more pleasant because the decel is much softer when I ease of the go pedal. I haven't had a chance to do any measurements to see if it is more efficient.
     
  3. NOLA_Mike

    NOLA_Mike Active Member

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    You don't need to set the regen to low you can control the amount of regen with the accelerator. And with it set to standard regen (not low) if you get into a situation where you need to slow down faster you can do it with regen rather than wasting energy by hitting the brakes.

    And as far as cruise control, that might help limit the regen but with the newer TACC it will use the brakes if it has to to maintain speed/distance to vehicle so I assume low regen would just result in using the brakes more.
     
  4. ThosEM

    ThosEM Space Weatherman

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    #4 ThosEM, Mar 8, 2015
    Last edited: Mar 8, 2015
     
  5. billarnett

    billarnett Member

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    Yes, I agree. But mostly there needs to be a way to make it much stronger so as to make it possible to avoid using the brakes except in emergencies.
     
  6. dirkhh

    dirkhh Middle-aged Member

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    There are two big challenges with that
    a) added complexity for the user: every new option adds decisions they need to make, concepts they need to understand. Admittedly we already have the two levels here, so maybe that wouldn't be a lot worse, but still, it's something to always keep in mind
    b) added complexity for testing: when making changes to the firmware the result needs to be tested with a broad cross section of the available option settings. So every new option that you add increases the number of combinations that you need to test which makes fw development slower and more expensive.

    Having said all this - I'd love ​to have stronger regen available. 90kW, anyone?
     
  7. billarnett

    billarnett Member

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    Yes, those are real concerns in general. But "a)" is largely ameliorated by having good defaults. And good documentation. And in this particular case it might actually be simpler to understand if it was just a continuously variable setting.

    "b)" is a much bigger deal in this case. But I suspect Tesla wouldn't have to test every possible value (of an infinitely variable setting) just the max, min and a couple of intermediates. And of course, not all options interact. You don't have to test all possible combinations of headlight settings, seat position and regen settings. Tesla customers have been asking for better control of regen for a long time (since before the first Roadster was delivered :) I don't know why they haven't responded.

    120kW. Or whatever the battery can take for a few seconds. Some of the superchargers are 135kW, right?
     
  8. saladman

    saladman Member

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    Regen is already completely variable with fine control of the accelerator. Set it to high, and modulate with your foot. I don't need another potentiometer in the mix.
     
  9. billarnett

    billarnett Member

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    I agree, actually. But others may not. Strong deceleration when backing off the accelerator is not something that most drivers are used to. Many complain. Perhaps the regen settings should be labeled Beginner, Novice, and Expert
     
  10. bhzmark

    bhzmark Active Member

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    Just use neutral to glide/slow slowly preserving momentum with no risk of regen inefficiency losses or need to feather the pedal hunting for the glide point. Except when going down a very steep hill at a speed where the aero drag losses would exceed the regen inefficiency losses.
     
  11. scottm

    scottm Active Member

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    #11 scottm, Mar 9, 2015
    Last edited: Mar 9, 2015
    Agreed that fine foot control with regen set on maximum gives the best control over various situations that you can recognize when the car can't, such as how far ahead the uphill portion of the dip is, and what speed do you think it would take to "clear it"....

    But this takes fine foot control. Have you tried driving in such situations trying to keep the regen gauge closer to "neutral" (hovering near the zero mark)?? On long hauls, foot fatigue sets in if not given a chance to rest it a bit.

    ICE cars glide so much on highways all the time, you can take your foot right off the go pedal frequently to relax it a bit.
    And there is no dilemma / choice to make about slowing versus storing versus coasting.. you just coast.
    You score a "free one" when there's enough momentum to clear an uphill bit without slowing down much below reasonable cruising speed by time you reach the top and resume from there.

    Emulating that behaviour, what gives the best yield in the model S, low or high regen setting is my question.

    Maybe it's necessary to take the person out of the equation, and say, locking the car on cruise control for the whole journey, what gives better yield ... low or high regen setting?

    It would be totally interesting to repeat that experiment with "regen completely OFF" if there were such a setting for highway.

    I also agree that too much variability in slowing / braking / regen response can be confusing for people. Maybe there's a need for "advanced settings". Anything that comes with a strong warning can all be grouped on that page. Like traction control OFF. That's an advanced setting. Maybe you have to be an experienced driver before the advanced settings page becomes visible. Like a user profile for the car would have to have gained X hours of driving time before those features are revealed to that user.
     
  12. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    If you get in the habit of resting the right side of your right foot against the carpet for a little friction and support as you feather the accelerator pedal for zero power, it becomes easy and second nature. In most situations, zero power is only needed for short periods of time, ~minutes. Before cruise control, we drove at a constant speed for hours at a time without complaint...
     
  13. scottm

    scottm Active Member

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    #13 scottm, Mar 9, 2015
    Last edited: Mar 9, 2015
    Maybe the feature I'm really looking for is "highway mode".

    Or maybe more control over cruise control for energy consciousness. I've often wondered, what if I could set the cruise control not for just a constant speed, but also for a maximum power surge draw? Two parameters. 100 kph at 40 kW would drive less aggressively on resuming or regaining speed than 100 kph at 60 kW. If you set the power draw lower than what the car needs, then you've power capped it and the car won't achieve the desired speed, during either acceleration or cruising. e.g. 120 kph at 20 kW, isn't going to do much more than 100 kph. And it might just crawl up a hill. Emulating an underpowered or overloaded vehicle. I think human sanity and patience would prevail. You'd stay over in the slow lane only for so long. And you'd be able to "boost" the car with a little more go pedal, at least to get over the humps in the road, while remaining on cruise so when you let off again at the top of the hill the car goes back into its cruise mode. Most people are familiar with this kind of occasional use of pedal while on cruise.

    If range is game for a particular drive, it might be comforting to know you can limit the average kW/h. Again, I know this is possible with judicious use of your foot on the pedal and various hypermile techniques. It would just help automate that.
     
  14. CHG-ON

    CHG-ON Still in love after all these miles

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    Love the comment on beginner, novice, expert. That's bang-on! I have found, with time, that I can pretty easily modulate regen with my go foot. One thing I have noticed, when using TACC, is that when it it set to 7, the regen and braking are much more smooth and predictable. I started with setting 4 and found the braking to more forceful than if I were to brake (Tesla or ICE). I have been worried that the guy behind me might not react quickly enough of the MS is hauling me to a stop in a short space. Going to 7 seems to eliminated that, though I have only had a chance to try it a few times.

    And while I have used low on the highway, I haven't had that much experience with it yet, as I am usually on country roads. I always leave mine in std regen except for the few times I have been trying it out on the highway and mountainous highways, such as 17 between San Jose and Santa Cruz, where it is much more pleasant to be on low for me.
     
  15. billarnett

    billarnett Member

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    Rather than mess with the regen setting, it seems to me that the best way to automate hypermiling would be to have another cruise control mode. Instead of just setting the desired speed one would also set a min and/or max speed. The cruise control would then do it's best to minimize energy use while maintaining the set speed ON AVERAGE and staying within the allowed range. (Of course, TACC would also come into play in traffic but that's an independent issue. )

    Aside: I wonder if TACC is good enough to slipstream a big truck safely. That could have a huge effect on Wh/mile. And with TACC it's possibly a lot safer. Though I suspect the truckers wouldn't like it if it became a common thing.
     
  16. bwa

    bwa Member

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    What kind of hills are these? Do you drop 1,000 feet in 4 minutes or is this more like a gentle drop? Do you usually have a lot of traffic with bad slow drivers coming way over to the left lane and suddenly causing you to slow down, or are the roads wide open? What kind of slowdowns are necessary?
     
  17. brianman

    brianman Burrito Founder

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    Efficiency Miser Mode
     
  18. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Meh.

    Regen isn't perfect and there are losses. Therefore, assuming you never touch the friction brakes, low regen will provide slightly longer range on highway trips vs. normal regen. How much? Unsure. To me, it's more of a PITA to change the setting than the recovery I imagine would be worth.

    If "low" causes you to touch the friction brakes more, obviously more aggressive regen would be better vs. throwing the energy away to brake rotor heat.
     
  19. jerry33

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

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    These are my thoughts too. In addition, there's the safety factor. If you need to stop suddenly, the standard regen setting starts some serious braking before your foot has a chance to stomp on the brake pedal. The only reason for low regen is to placate those folks who insist a car behave like an automatic transmission car.
     
  20. scottm

    scottm Active Member

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    #20 scottm, Mar 15, 2015
    Last edited: Mar 15, 2015
    Thanks to all that answered.

    Here's my take away about this thread's opening question... use low regen setting on open highway trips, drive using pedal inputs that minimize power swing and try to center around neutral energy on the gauge when modulating over hills and bumps, momentum is a better use than storing energy always, and use the brakes hard if when needed to stop the car now.

    I get that it's more a function of how well you use the pedal vs the regen setting for range boosting.

    But having it set to low regen is a better safety net for when you forget sometimes and do a sudden full lift off the pedal, or just want to rotate your ankle and give your foot a stretch... and there is no need to be slowing down.

    In fact, the best setting would be OFF but that's not offered.
     

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