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Black Ice and Regen: bad combo?

Discussion in 'Model S: Driving Dynamics' started by scottm, Nov 13, 2015.

  1. chickensevil

    chickensevil Active Member

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    Yes, I realize that people are generally not looking down at the dash when they are trying to avoid losing control of the car, they are instead looking out ahead at the road trying to use what little muscle memory they can muster to make the car do what they want it to (stay on the road) while under somewhat of a panic. But yes, I do know that it cuts power to regen, because under severe conditions you can visually see the green bar fluctuating even though you may have your foot completely off the peddle. And under less than severe situations you can still feel those minor adjustments, even if the response time of the display is unable to keep up.

    This was why I suggested to go purposefully make TC and ESC kick in either under breaking or just regen under a somewhat safe location (open parking lot, straight wide road with no traffic) and watch what happens from the dash. You will see that just as the car controls acceleration under slippery conditions, it controls deceleration in the same way. That is, it will cut power (stop regen) until it can detect appropriate traction to try and pull the car under control again.

    There is a road course that everyone takes their cars to, I believe it is a giant frozen lake in Norway or some such... wherever it is, it is *the* place to test your car's winter performance, and it is where Tesla took their car to tune it for winter. Normally a manufacturer has to make multiple visits because they test a configuration, take it back to the shop make some adjustments, and then set out again to test it. Tesla on the other hand was able to fit, from start to finish, the entire process into one visit at the lake. This is because the mechanical part of the car is very basic as compared to an ICE. Electricity is pulled from the pack, through the inverter, and into the motor (or the opposite when under regen) which can be controlled as a 1 Amp draw all the way up to a 1500 Amp draw (on a Ludicrous enabled Tesla) at ~480V (the volts fluctuate depending on the state of charge on the pack but not by enough to matter as it relates to this). The result is the ability to direct very fine tuned power draws from the pack of under 1kW all the way up to a maximum of 400kW all within milliseconds. This then translates into mechanical motion that is coming off the motor, into a fixed speed gear box, into the axle that spins the wheels. Everything from that point is controlled with electric motors wired into the computers of the car, and you can adjust the programming of that computer on the fly. In the same way that you cannot detect latency between your mouse movements and keyboard strokes on a PC, is the same thing that is happening on the car level. It will adjust the spin the each wheel to control the traction of the wheels and their contact with the ground.

    Some of these adjustments are happening so quickly that the dash LCD doesn't have a quick enough response time to even light up the TC on the dash, but you can feel the wheels, motion, peddles, and steering wheel and know that things are happening. Let that sink in for a moment. Things are happening so quickly, that even when you FEEL it happening you can't SEE it happening because it is happening quicker than what the car can send a signal to the dash telling it to turn on the TC and it showing up. That light going off is likely tied to a measly 50 or 100ms response, and yet the car is doing things within that window that can be felt, but not seen.

    This is why everyone praises the RWD handling of the car, most suggesting that it responds better than some AWD ICE cars that are on the market. And of course an AWD Dual Motor Tesla can go toe to toe with the best of the best on the market like Subaru (I would love to see a rally spec'd Tesla cause I have a feeling it would rock the socks off a Subaru).
     
  2. DFibRL8R

    DFibRL8R Active Member

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    My only issue with regen in the rain is the fact that with the Model S I rarely need to use my brakes especially in highway driving. I have had a few unnerving incidents where I need to make a sudden stop and the brakes are waterlogged from lack of use and I get a feeling that no matter how hard I push the brake, nothing is happening. After a short time (1-2 seconds but seems like longer in the moment) things work ok. I now try to periodically tap/dry the brakes and of course leave extra stopping distance in rainy weather. This is a problem that I believe could be addressed through automation where the brake is automatically lightly engaged every (10 or so ?) minutes while traveling at speeds in rain (possibly using rain sensor for the wipers).
     
  3. AWDtsla

    AWDtsla Active Member

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    This exactly my point. Dry performance is routinely experienced by engineers, and snow/slippery/loose surface was done for one day. The engineering loop must consist of daily driving with hundreds or thousands of hours of experience in these conditions. Otherwise what happens is predictable. There's a steady stream of people that have experienced outliers in performance (read: soiled underwear)

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    Audi does this. However that reminds me, another reason for regen disable is to be able to "clear" the brakes. Let's say after the car's been sitting a a couple days and the rotors are completely covered in rust. Or because they have a layer of water on them on the highway.
     
  4. DFibRL8R

    DFibRL8R Active Member

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    There's a big difference between feeling out of control in a black ice situation and actual loss of control that results in a departure from the lane/road or a collision. I have experienced the regen on ice feeling out of control once in 64,000 miles of Model S driving (DC area so we do get some winter). For me, I felt the car fish-tailing as I decelerated from highway speed onto an icy exit ramp at night. Unnerving but unscathed. I initially had the same concerns as the OP, thinking that I know not to touch the brakes in ice but the Model S is foolishly "braking" with regen from a simple pedal lift triggering a slip. Now I realize I am better off trusting the reaction time of TCS in this rapidly changing situation than my own ability to recognize and apply the correct inputs in a beneficial way.

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  5. Han Chen

    Han Chen Member

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    My situation is not actually black ice but we just had a big dump of snow overnight. I found the regen to be disconcerting when I was trying to slowdown on icy roads. Turned regen to low and it is much better.
     
  6. ecarfan

    ecarfan Well-Known Member

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    "for one day". Really. And you know that because...?
     
  7. AWDtsla

    AWDtsla Active Member

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    Because of Elon Musk saying so and also numerous articles. Maybe they got 2 days. 3 days.. 4 days.. who cares? You can effectively round down to 1. How about continual winter driving for months out of a year.
     
  8. brianman

    brianman Burrito Founder

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    You didn't fully answer his question: Does BMW allow you to disable ABS?

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    Never heard of or seen this.

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    I disagree. This implies that every time I drive my cold-soaked Tesla, I should get the same warnings and prompt because the car already turns off Regen in that situation.

    So, Andy will like this one: Perhaps the solution to "I don't want regen" is just to cold-soak our cars before driving through icy conditions. /rolleyes

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    + 1

    On I-90 between Renton and Ellensburg in the winter, standing water is common (and the signs warn about it). The must unsafe I've ever felt in a Tesla was in my P85 with cruise control on going through those puddles. (I ended up turning off CC in such situations because it makes me queasy.) In both the P85 and the P85D, despite the human comfort factor the car is very composed in such situations.

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    This is what passengers are for. They (usually) have eyes that can look at the dash while you watch the road.

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    You know this how?
     
  9. mknox

    mknox Well-Known Member

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    What type of winter tires do you have? That can make a difference here.
     
  10. tomcherv

    tomcherv Member

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    Happy to hear your daughter was OK.

    As far as how Black Ice is created, it is both - thank you for bringing it to my attention - I learned something new. I researched Black Ice and the I-35W bridge in Minneapolis was specifically mentioned as well as several other Minnesota references. Here in Minnesota, the primary cause is vehicle exhaust, the I-35W bridge is near a waterfall gets it from water spray and dew as well.

    It's called Black Ice because it is a thin layer occurring at cold temperatures (below -18C/0F) and indistinguishable from pavement that is simply wet.
     
  11. chickensevil

    chickensevil Active Member

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    I think you were taking what I was saying a bit out of context, that or what I implied is not what I was trying to. I didn't mean to suggest that was the only testing they did, what I was implying is that something which takes a very long time to figure out and perfect in an ICE was able to be done in a short window because of the simplicity of the route to go from the computer saying: "make adjustments" to the wheels receiving those adjustments. The reason other cars take longer to tune those is because you have to physically make adjustments to parts of the car as opposed to updating some lines of code.

    ICE maker: do a couple runs, take it back, make adjustments, come back another day, do some more runs... Etc
    Tesla: do a couple runs, make adjustments on the spot, do some more runs.

    Assuming they both required the same number of runs, Tesla completed it in quick fashion simply because they couple reprogram the car on the fly. You are still getting the same amount of actual TEST time, just less delays in between. That was all I was implying with my comments.

    And you coventiently discarded the rest of everything else I said to focus and nitpick on that one line. Nevermind that I stated that people have compared the overall performance of the RWD Tesla to being on par with an average AWD system. No no, lets ignore that and cherry pick a comment to suggest that I was implying that Tesla didn't do enough testing... Sigh...
     
  12. Lyon

    Lyon 2016 S P100DL, 2016 X P90D

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    I was actually just thinking about this topic the other day but in a different context. I had lifted off the accelerator and was moving over to the right to get into a turn-only lane when I passed through a thick pile of wet, churned up leaves. It was rainy and in the 50s so no ice. The rear end definitely got a bit squirrelly on me for a brief moment as I was moving my foot to the brake pedal. It happened very quickly and I'm not sure if my steering input (into the slide) or the cars safety controls (or both) contributed to the quick restoration of proper tracking. Needless to say I will be more mindful of leaves and reduced traction situations in general. I hope to find a snowy/icy parking lot with nothing in it this winter to do some experimenting.
     
  13. green1

    green1 Active Member

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    And this is why I've never understood why people can't tell there's black ice around. Who in their right mind sees a road at those temperatures and thinks "nah, it's just wet!" anything that looks wet at those temperatures is ice, it's really easy to spot "black ice" as "wet road" is simply not an option at those temps!
     
  14. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    Err...I've logged over 1 million miles of driving, an awful large percentage of that during the bottom six months of the years. MY only surefire safe way of determining if a road surface is dry or black-iced is to come to a slow, safe stop, stick my foot out, and test. Trusting to eyes is foolhardy.

    Some other dangerous advice I've been reading in prior posts is that black ice is a phenomenon occurring only around the 0ºF/-18ºC mark - this also is incorrect. A veneer of ice can easily occur, for example, during a thaw: road surface is nicely below freezing---> air warms up and generates fog--->that moisture contacts the cold road and whammo-blammo, all of a sudden that 16,000-lb trailer you're hauling decides it wants to lead you down the road.
     
  15. green1

    green1 Active Member

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    I don't think I have any form of super-vision, but I've never seen a road that looked dry and was icy, I've seen many roads that looked icy and were. I have plenty of experience driving in winter, and where I live is famous for it's freeze-thaw cycles that generate lots of this sort of ice. It's easily visible every single time.

    I do "test" the surface when it's nearer the freezing point and I can't tell if it's wet or icy, but when it looks dry, it is.

    Ice simply doesn't look like dry road, it never has, and never will. "Black Ice" is very obvious, people who ignore it need to pay more attention to the road.
     
  16. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    You seem convinced of yourself, so I'll not try to change your mind but I absolutely will not allow bad advice to flourish on this forum without comment. There are many times when what is on the road surface is not obvious. Lighting conditions; age and wear condition of asphalt; fog; alternating patches of cold road/warm road, esp. in hilly terrain; warm(ish) rain hitting a cold road - it can look wet but that can be moisture atop ice that is slicker'n otter snot. The only part of your post I'll endorse is that ultimate clause.
     
  17. green1

    green1 Active Member

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    Exactly! it looks WET but is in fact ice, it never looks DRY.
     
  18. Wackybroad

    Wackybroad Member

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    In New Enland I driven nothing but an SUV. But am determined to get a CPO. Any one get snow tires? And I hate to sound dump -Regen?
     
  19. chickensevil

    chickensevil Active Member

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    Quite all right, Regen is a form of braking. It is like engine braking on a manual transmission (and feels very similar to throwing the car into 2nd gear at 50MPH, only in this case you keep that hard braking power all the way down to 5MPH where it cuts off). Except what this is, instead of wasting that energy into heat or some other loss, they are reversing the process of the electric motor so it goes from being a mechanical generator from electricity into an electric generator from mechanical energy. Thereby you take your forward momentum and put it back into power in the battery. All electric cars (including plug in hybrids) have implemented regenerative braking into their cars. What makes Tesla different from most is in HOW they implemented it. Instead of controlling the braking on its own pedal (physical brakes as well as Regen brakes) they have left the physical brakes on the brake pedal and put Regen control into the same pedal as the accelerator.

    To control it, pressing in the pedal fullway will enable you to go faster, coming off the pedal about 3/4 of the way back is your neutral (or coasting), and coming full off the pedal is full Regen.

    What this enables is what we call one pedal driving. This is because you generally are able to drive the car through controlling just the one pedal because the Regen braking is strong enough that you don't need to use the actual brakes.

    The point of this thread was then the discussion surrounding traction control (TC), Electronic Stability Control (ESC), as well as the other means the car might us to ensure the car stays going where you want it in adverse conditions. Specifically as it relates to regenerative braking given the unique nature of control, and the habit of people to come off both pedals when loss of traction starts to occur (or others I suppose go full on panic and pointlessly slam on the brakes making it worse.
     

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