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Regenerative Braking

Does anyone know if the regenerative brake will have an adjustable setting for more or less braking?
I am assuming that more braking increases the amount of energy recovered. City mode highway mode?

My preference (as if anyone asked) would be to have little to no regen on the accelerator pedal. If I need to shift my foot off for a moment, I don't want to feel like I'm hitting the brakes. What I'd prefer is something akin to the normal slowing engine compression causes when you take your foot off the gas pedal in an ice vehicle, down to just the air and rolling friction you get when you go into neutral on a manual tranny.

Coasting is inherently more efficient than regen (I'm sure this statement will generate some back and forth). While regen does convert motion into power, it does so at a loss (80% efficiency more or less). I can then use that juce to speed up again, but why not just coast? I don't have the regen loss, only the normal rolling and air losses.

Now I do want regen on the brake, and I want it to max out as much as possible before having to brake with friction (that's at total waste). Wonder how that handles, however since all regen will come from the rear wheels, and in conentional cars a disproportional amount of braking comes from the front wheels. Will braking function be better on a Tesla, especialy on curves and different traction surfaces? Looking forward to seeing...

@jbunn - Yah, that's my A description. As previously noted, I'd prefer that as well.

I think all that should be said has been said in this and the other thread linked above. I'm trying hard not to repeat everything over and over... But here's one aspect that has not yet been mentioned with regard to its effect on regeneration:

Wonder how that handles, however since all regen will come from the rear wheels, and in conventional cars a disproportional amount of braking comes from the front wheels. (

The main reason for the disproportional amount of braking on the front wheels on ICE cars, as far as I know, is weight distribution. For one, usually the engine weight is on the front wheels, but what's even more important is a relatively height center of gravity that shifts most of the car's weight to the front axle under deceleration.

This is entirely different in the Model S, because the weight distribution between axles is 50:50, and this proportion does not change much under deceleration thanks to the extremely low COG. Therefore, I'd assume that even under deceleration, the rear axle should be responsible for almost 50% of the available traction (maybe even more, if different tires are used on the driven axle), which is a good thing to start with for regenerative braking (which inherently only affects the driven axle).

This of course only covers braking on the straight. One would hope that traction control is smart enough to release regen before the car suddenly oversteers when using regenerative braking in a curve. In fact, Roadster owners reported that the Roadster does precisely this, but it can be a bit hazardous because the driver must react quickly and put the foot on the brake pedal to engage all four friction brakes in this situation, otherwise the car would move on unbraked.

I don't drive around constantly slowing and re-accelerating, unless there a traffic-based reason to do so. No one is stopping you coasting; your foot just sits in the right position to not provide current to the motor! I tried this last night, the hardest part was dividing my attention between the ammeter and the road. But I'm an instrument rated pilot, so even that wasn't terribly hard.

Anyway, I'm bowing out of this discussion now. I'm talking from my experience driving four different kinds of vehicles (Roadster with regen, automatic, manual including engine braking and coasting, and large trucks with valve lifters). Roadster-style regeneration IMNSHO is just wonderful.

Nothing to complain about here? Time to move on to another topic until test-drive-time.

Nothing like reality killing a perfectly good topic of conversation. :)

I currently drive a Mitsubishi iMiev. Yeah, it’s not a Roadster or Model S (16 kWh battery, 0-60 in 13 seconds) but it’s an EV with regen. It has three modes for driving forward: D, B and C where D (drive) is normal, B (brake) is extra regen and C (coast) is less regen. I use D 99.9% of the time, B a few times when going down really steep inclines. I have never used, and I’m sure will never use C mode for the reasons described well in this and other threads by anyone who’s ever driven an EV (NO NEED!).

However, one thing comes to mind: My ICE (yes I have one of those as well) is a Volvo. It has a function called HDC (Hill descent control) which basically is just a sensor that senses when the car goes downwards really steeply and gears down more than normally when you let go of the gas pedal in order to get maximum engine braking (the ICE’s nearest equivalent of regen). I think it’d be cool to have feature like this in any EV. Maybe especially in the coming Model X which will be more “sports” and “off road” oriented?

Not to try to take anything away from Tesla's engineering, but as a software engineer I don't think having a moving range of coasting before regen based on pedal position is very difficult. You simply keep tabs on the position of the pedal and use a (probably constant, but it also could learn) threshold or multiple thresholds to ensure that small variances keep the power regulation to the motor at the same rate. A let-off within a certain range is interpreted as coasting, and once you leave that range, you're in regen which should increase intensity as you let off more. Any time you reach regen while letting off or reach a faster speed while pushing the pedal further, the values the thresholds are based would update... All this would of course happen many times per second.

I would imagine the difficult parts are in controlling power rates / frequency to the motor and regen rates rather than when coasting should begin and when regen should begin. Not to mention how the battery pack charging and energy consumption has to be balanced out.

Another way of saying it: I think interpreting what to do based on pedal positioning is probably fairly easy, but going from what it needs to do to determining what fine adjustments are necessary to carry it out isn't.

I'll say it again.... if you haven't driven a car with regen on the accelerator, don't knock it. You'll be surprised. I greatly prefer the driving experience with it.

Since the X will have 4WD, that changes the calculus, as it means 4WRegen, too. I assume there are some (not drastic) differences in COG and such that will affect how it drives. Interesting comparisons coming soon!

Single-pedal driving: easy

Like the Tesla [Roadster], the [BMW] ActiveE is easy to drive on a single pedal. The regenerative braking is relatively aggressive, but very well modulated, and it takes only a few minutes to learn just when to lift off so the car comes to rest just behind the car in front at a stoplight.

If the needle in the energy meter is exactly vertical in the "Ready" position while underway, the car is gliding, using an accelerator position drivers learn to find when they want momentum to carry the car as far as possible without the slowing effects of regeneration.

If the needle in the energy meter is exactly vertical in the "Ready" position while underway, the car is gliding
Having that visual feedback in the Model S would be very helpful, at least until we learn to feel it intuitively.

Robert, have you driven the roadster? I have, and 10 minutes is about all it takes to get the "feel". It is amazingly intuitive.

+1 dborn. In my experience, only people who've never tried it complain about regen on the accelerator pedal. Those who have love it.

Also, not that you need it or anything, but there's a nice big power meter in the Roadster's instrument cluster. When it reads zero you're coasting.

At the factory event I was told that there would be a small amount of creep. Now that the roads are icy in South Bend I am hoping there is very little or no creep. I remember my car accelerating, while pushing on the brakes and the front wheels locking. I had to put the car into neutral to get it to stop.

I am not trying to argue if regen is better or intuitive but allowing true costing (no torque applied by the engine, no regen) is always more efficient than regen because regen will never capture all the energy back. None of this will make any difference once you come to a stop at which point both will be the same.
(You would have come to a stop earlier with regen but with more power in the battery pack vs. driving further with less energy left.) To travel the same distance, starting from a constant speed, letting the car coast will be more efficient. Not always practical in real life of course. This doesn't work for stop signs (you are coming to a stop) but coasting would help when you can anticipate you have to slow down slowly for traffic ahead but don't need the regen to slow you down (more than the rolling resistance and wind resistance)

I heard from a reliable source that the Model S alphas and maybe the betas had regen adjustable by the driver. Whether they leave that in the production vehicle is another matter, of course.

While you're correct that maintaining as close to constant speed as possible will be the most efficient, I have every intention of doing almost the opposite when I drive.

  • Given the fun of jumping out to a quick start,
  • knowing I'll get much of the energy back with regen, and
  • understanding that the value of the total energy lost is negligible with respect to what I usually do (even if I try to save as much gas as possible) in an ICE car,

I'm hoping to have more fun than ever before while knowing I'm wasting almost nothing.

Let all the other drivers think I'm wasting gas.

Yeah, it will be real hard for some to get over that "hypermiling" mentality in normal driving. However, on borderline range-runs it will come back full force!

VincentA, we can legitimately assume that regen will be user-adjustable in the Model S:

By luck, one of the first I introduce myself to is Drew Baglino, who happens to be directly involved in setting up the Model S regen braking system. [...] When I pleaded for driver-adjustable regen on the Model S, he said this was under consideration. (Two days after the event, while writing up this report, on a whim I e-mailed Tesla boss Elon Musk and repeated my plea for driver-adjustable regen. Three hours later, I got this reply: "I totally agree that regen should be driver-adjustable and it will be on Model S." The message was Cced to JB Straubel, Tesla CTO.)

Yes, ask and you shall receive. : )

unless you ask for saddle leather...

It's finally official. Regen will be user-adjustable, from day one:

"One of the engineering advantages that make an EV better than any gas-powered car is regenerative braking. When you take your foot off the Model S accelerator, energy is fed back into the battery, which causes the car to slow down (a similar feel to downshifting with a manual transmission). One of our Firmware engineers wrote a great blog about this technology shortly after the release of our Tesla Roadster. Over the past few years, we have learned that not everyone likes the same amount of Regen. Some owners like a little more resistance, some like a little less. Having less Regen means you will likely get less range, but some people still prefer the feel of their car with less Regen. We listened to your requests and I’m pleased to announce that Model S Regen will be adjustable. You can adjust Regen to suit your driving style."

Cool, the question is, what amount of regen is right for you? Having no frame of reference, I have no clue about it! I would think I want MAXIMUM regen to both save brakes and get the most juice pumped back into my Model S batteries. Any arguments against that idea?

@BYT it will probably depend upon the scenario. In traffic / around town, I agree. On the highway you may chose more glide and less regen. I expect I'll play with it to find the right mix.

Agreed, how awesome if we can have a quick flip of regen settings for highway vs. street driving because most of my driving is in roads and I do hit the highway briefly on my daily trips. I can't wait to get a real world feel and see what everyone has setup for themselves and why!

Love the user-adjustable regen feature. Having test driven a Roadster, I can say it was quite dramatic as compared to the regen in my Camry Hybrid, which is not.

At the Newport event a few weeks ago, GeorgeB said that they want to ask owners to at least try the "standard" (maximum) regen for a week or so before adjusting it. As I have said before and elsewhere, we're leaving it alone... it only took about 15 minutes to fall in love.

does anybody know if it is adjustable "on the fly" It would be cool to adjust to minimum as you enter the freeway.

"... adjust to minimum as you enter the freeway"? I don't get it. It's freeway driving where I think it comes into its own! Those random "pressure waves" of brake lights when you can't see any reason for them, or the 0-30 traffic jams...

The steering is also adjustable, from firm to sloppy loose soft. Someone suggested making it speed-dependent.

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