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Is coasting retarded like it is on the Roadster?

I understand that on the Roadster, regenerative braking becomes active when the accelerator pedal is not pressed enough to maintain speed and that as a consequence, coasting functionality is retarded. I also understand that unlike the Toyota Prius, the regenerative braking in the Roadster is not in any way linked to the brake pedal.

Telsa has some very promising technology, but these are issues that impair the driving experience enough that every time I think about possibly getting one, I tell myself that it is not worth it because I cannot coast without having the regenerative braking activate.

Does anyone know if these issues have been fixed in the Model S or does Tesla Motor still consider them to be features? If they do consider them to be features, is it possible to turn them off?

I've got a Roadster and in my opinion the way regenerative braking works in the Roadster is vastly better than in the Prius. The control of your speed is far finer and faster than with the Prius. If the model S were to work the way the Prius does, it would be a substantially less attractive car to me than if it works the way the Roadster does. Obviously different people can have different opinions and not everyone must like the way the Roadster works, but do not assert that it is a defect that needs to be fixed.

If you haven't driven a Roadster, I recommend you try it.

Are you kidding, have you actually driven a Roadster? The accel/regen pedal is wonderful to use. One foot driving most of the time - you hardly touch the brake pedal. When I switch back to an ICE car I really miss it.

I agree with SteveU and Douglas3. I test drove a Roadster and found the regenerative braking one of its top features. I'd go so far as saying, I would cancel BOTH my Model S reservations if the regenerative breaking feature is discontinued from the Roadster to the Model S.

Look at it this way: there is no clutch or transmission in an electric car, so how do you think such a car could even be ABLE to coast?

Vawlkus, I do not think there is a technical reason why an EV should not be able to coast. Even an electric motor could be free wheeling. It is a matter of intentional user experience design. I am not saying it is particularly good or bad the way it is in the Roadster, just that there is a reason for the way it is that is unrelated to technical constraints. And it is certainly important to get the details right. Just how much is the car slowed down by lifting the pedal to a certain degree -- as much as the designers must tweak this behavior, as much it is impossible to tell if it "feels right" without actually trying it in a real life car.

Something that nags at me about the regen (non-accelerating) mode that makes braking unnecessary until you need to bring the car to a complete stop, like at a stop sign is that until one actually has to step on the brake, there is no indication to the cars behind you that you are slowing to a stop, like there is with an ICE vehicle. Maybe it would be a good idea to have a way to illuminate the brake lights when in regen in a phased manner, make them light up brighter when the vehicle slows to a stop, and then steadily brightly lit when stopped. It bothers me to not be able to warn those vehicles behind me that I intend to stop, and I think I'd really be upset if somebody rear-ended me because they didn't see my brake lights.

Interesting, PatriciaS!
I live on a 1700' hill. It is 5 miles to the valley. I drive an ICE vehicle. And when driving downhill, I NEVER put on the brakes. I use lower gears to decelerate for hills and curves.
I have never had anyone get excited about not seeing brake lights burning on my car. We as humans have a neat thingy called a brain, and the brain is able to detect objects moving nearer or further away. If anyone rear ends me because they didn't see my brakes, California law holds them liable, not me. If I am stopped at a light, and getting ready to go when it turns green, my brakes are not on. If I am maintaining my speed, or decelerating, my brakes are not on.
By the way, Tesla has arranged that the brake lights go on with deceleration with regen. So you're covered. I'm not worried about the lights, but I am with dragging my brakes off, as many of our out of towners smoke the brakes halfway down hill.

Roblab was a bit snarky about it, but he's right. Many sports car ICE drivers use engine braking pretty heavily, which has no brake lights, so a car slowing down without brake lights is nothing new. Tesla, as he noted, even causes the brakes lights to come on if the regen slows you down enough.

Cool safety feature = Brake lights coming on due to heavy re-gen effect.

Less chance of getting hit from behind.

The brake lights on the Roadster DO come on during regen braking except in areas where it's illegal (I forget where that is, offhand).
I find the regenerative braking (without touching the brake pedal) one of the primary reasons I absolutely enjoy driving the Roadster.

@bgoodwin, wow, it's amazing to think that there's a law on the books somewhere that prohibits brake lights coming on for re-gen effect.

Wonder that the reasoning is?

It's pretty easy to go from 50 to 30 in quickly with a downshift (re-gen aside), which is a receipe for a rear ending.

IMHO, any heavy deceleration should come with an indication of some kind. Brake lights seem the obvious choice.

The law is not somewhere. It's all over Europe. European Roadsters don't have the brake lights coming on by regen. Many people told me it's not a great problem, but I already fear one of the "I have to drive as close as possible"-jerks hitting me.

Really? Where in Europe? European cars require separate turn indicator (yellow) which is not in same circuit with brake lights, but not turning brake lights on with regen was news to me.

For those who have driven a Roadster, how does it handle going downhill if you take your feet off of the accelerator say while on the highway on a steep downgrade?

I too, use gearing down to slow my car. If you think of doing that as being a mild form of regenerative braking (which it is, just without the power going to the battery in an ICE), then you should get the idea

I haven't driven a Roadster (really must arrange to do so...), but I have driven an EV-1 for 2.5 years and a RAV4-EV for over 7 years. Both cars were capable of coasting, and IMO it's an important way to drive efficiently.

I think it's fine to be able to control both regen and acceleration with one pedal (EV-1 could do this as well and I used to use it), but I'd like the option to simply coast as well, perhaps via a button on the shift lever.

Why do you think coasting is an important way to drive efficiently? Based on what assumption?

BYT if you take your foot off the accelerator on a downhill, it slows down. Regen is a lot like downshifting a manual transmission into 1st gear - it's quite strong.

well coasting is just a matter of finding the sweet spot between accelerating and regen
so Tesla only have to add maybe 5% of the speeder movement to coasting

0-5% strong regen
5-10 medium regen
10-15% light regen
15-20% coasting
20-40 light accelerating
40-60 medium accelerating
60-80 strong accelerating
80-100% insane accelerating

In my current ICE I do a lot of coasting. If I see traffic ahead is slowing I'll hit the clutch and coast for a bit to see if it speeds up or I need to brake. If I see the traffic light ahead has turned I will coast until I need to brake or the light will turn green and I won't have as much acceleration to do to get back up to speed.

Somewhere there is likely a balance between coasting and regen vs the energy required to resume travel at the speed you were using before you had to slow down.

Driving style, patience and the ability to anticipate what is happening around you will all factor into which you can extract the most distance from.

IMHO that's a bad idea. When faced with a similar situation I'll take my foot off the gas, but I'm keeping the car in gear incase the moron behind me isn't paying attention and I need to avoid him.

cablechewer, if I'm driving my Roadster and traffic slows ahead, I lift up the accelerator a little. Depending on where I set my foot, I can essentially coast, slow down a little, or speed up a little. You really have quite precise and instantaneous power control.

Also I feel there's an extra margin of safety if you have to go for the brakes. As soon as you lift your foot the car is decelerating and the brake lights are on - even before you get your foot on the brake! That's gotta be a good fraction of a second faster than in any other car, and it gives you that little bit of additional safety margin in a panic stop.

Also I completely agree with Vawlkus. Way back in driver's ed they taught us not to do that as you sometimes need to apply power to avoid an accident, and engaging the clutch takes extra time.

I, too, drive mountainous terrain in an ICE, using the tiptronic option on my tranny, downshifting rather than riding the brakes, but I live in an area where there are a lot of twits that tailgate, so I resort to tapping the brake to get them out of my tailpipe. I think there will be a short learning curve to learn to drive an electric, non-coasting, regen-braking vehicle, but I certainly look forward to doing so!
Douglas, I'm happy to hear that you get brake lights when you are off the accelerator. I know it's the tailgater's fault if he hits you, but who needs the aggravation?
Basically, driving defensively and with anticipation, not making any sudden moves, is the best policy. Too bad not all drivers actually do it.

Interesting detail in this article:

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.)
http://www.thetruthaboutcars.com/2011/10/tesla-model-s-customer-blog-bet...

Regarding coasting vs. regen, when I read about the BMW i3 I came across an interesting idea. Tesla, are you listening?

Personally, I think I would like strong max regen as a means to do "single foot driving" -- regen should be smoothly adjusted according to the position of the pedal, and should be strongest when the foot is almost lifted from the pedal. So far, so obvious, and my test drive in the Roadster convinced me that Tesla has a very good idea how to implement this and make it feel very natural.

Now for coasting. With the implementation outlined above, as it can be found in the Roadster, there is a very fine line where the car coasts or sails with neither propulsion not regen being active. It is almost impossible to hit that point with the pedal, and keep it there. Therefore, BMW seems to suggest for the i3, that the drivetrain is disconnected from the wheels and the car supports perfect coasting when the foot is actually lifted from the pedal. Put the foot on the pedal -- ever so slightly -- and regen kicks in, lift it off the pedal, and the car coasts.

Of course, electronics need so smooth out the behavior, i.e., regen should be slightly lagged and should then be applied smoothly, so that changing directly from propulsion to coasting or vice versa does *not* trigger max regen in between.

Does this make sense to you?

In BMW's words (emphasis mine):

[...] The electric drive also allows for deceleration by means of the accelerator pedal. After the driver eases up on the accelerator, the electric motor acts as a generator, converting the kinetic energy into electricity which is then fed back into the battery. Energy recuperation generates a braking effect which makes a significant contribution to vehicle deceleration.

A coasting mode makes this unique "single-pedal control" of acceleration and braking using only the accelerator even more user-friendly. When the driver eases off the pedal, the electric motor's zero torque control keeps the drive train disconnected as long as the pedal is in this position. The vehicle now coasts without consuming power, driven by its own kinetic energy.
http://www.bmw-i-usa.com/en_us/bmw-i3/

I would believe that your suggestion does not work, but BMW implementation does. They apparently have separate "coasting mode".

What you suggest would cause crashes in city traffic. You lift off your feet to regen and when car in front of you starts to get closer you lift it a bit more and hit the coasting (IE leg no longer causes pressure in pedal) and suddenly car does not slow down anymore.

Human reactions are too slow to prevent accidents there and your first reaction (press a accelerator a bit more to hit regen) might cause car to accelerate instead of decelerate and accident is ready.

It would be d*mn confusing to go from max regen to no regen.

I would believe that your suggestion does not work, but BMW implementation does. They apparently have separate "coasting mode". (Timo)

Something went wrong communication-wise. I apologize. To be entirely clear: I wanted to suggest the concept precisely as outlined by BMW.

At first I had only the German text available so I tried a translation myself. Two sources for error here: Obviously, my translation, and less obvious but undeniable, the possibility that I do not fully understand BMW's concept.

That said, I had the same concerns as you when I first read about it, but thinking about it my first reaction would be "hit the break pedal", not "hit the accelerator pedal to slow down quickly". Seems safe enough to me.

The logic supplement to this concept would be to make the break pedal trigger regen, too. It all sounds very complicated, and it certainly is, implementation-wise, but if done right I expect it could all appear very simple and natural for the driver (and thus would be safe).

I agree, that would be a horrible implementation. When I lift my foot off the pedal, it's only because I want to slow down or my foot is headed for the brake.

I do want max regen on the accelerator pedal. Like you said VB, that allows for one pedal driving most of the time, except when either coming to a complete stop or for an emergency slow-down.

In the latter case, the max regen is a great safety boost since max regen is slowing the car already, before your foot even makes it to the brake. That shortens the emergency stop distance considerably!

I like the idea of having the regen level controlled by the foot.

Previously, I had suggested that the amount of regen be programmable, and, further, that an app be available to attach to a steering wheel function to allow control. Hold an "increase" rocker bar to increase regen, "decrease" half to lower it.

It could be implemented as an overload (reuse) on the same switches that operate the cruise control, a system that would not be in operation when the car is slowing.

The predefined level of regen would kick in each time, but the rocker switch could increase or decrease that level until the brake (or accelerator?) was operated.

I still like that idea, but if it can be implemented with the accelerator pedal instead, all the better.


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