Why regenerative braking belongs on the brake pedal

[SageBrush]

I have been told that Volt L is somewhere between Tesla Low and Standard regen. I was not a L driver (didn't like it), so once I found out Tesla doesn't give you the option for regen on the brakes at all, I decided to start "training" so that I will hopefully have a smoother transition.

Do you have difficulty gauging the how far the car will travel on an incline when you take your foot off the go pedal ?

Honest question -- I'm trying to understand.

I view regen that way, as an additional slowing force on the car. If it is not enough, I add more by using the brakes. <<shrug>>

Otoh, I've watched my wife drive and she coasts very, very little. It will be interesting to see if she has difficulties with the Tesla.

 

[Craig9080]

Really? empirical rebuke of the science? The OP is preaching to us ignorant folks about basic vehicle dynamics 101 on throttle response, weight transfer and loss of traction, specifically to the rear wheels and oversteer. The OP fails to provide any empirical evidence regarding said dynamic vehicle response on a Model S or X.

The OP's essay is very much correct on what can cause oversteer and understeer. However, the Model S and X have a huge amount of weight below the axles and centered between them. The weight transfer from regen is not the same as say tapping the brakes on a RWD Ford F150 on icy pavement. The regen is nearly the same as driving a manual transmission and lifting your foot of the gas or downshifting on an auto.

Unless you know how to heel toe, most drivers in an emergency will hover over the brakes first, but there may be situations where you'd need to accelerate out of a situation. In a Tesla, you have very fine control of both regen braking and if you need to accelerate out, there is less of a need shift between the brake and the accelerator.

According to Tesla, the Model S has a 48% front 52% rear weight distribution, it is a reverse pendulum-but not much of one. An F-150 has a heavy engine up front, a large cabin, and then an empty box at the back. I could not find anything on it's weight distribution (because no one cares about that for a truck) but it is definitely front heavy when unloaded. An F-150 will default to under-steer in limit handling situations due to the weight distribution and even in the event of power over-steer (assuming you are actually traveling forward and not trying to do donuts) the large amount of weight up front and the lengthy wheelbase will help fight the effects of over-steer.

The Model S will have a tendency to rotate under rear slip events either under power, braking, or regen due to the ~186lb weight imbalance to the rear. Again, this is actually not a bad weight distro for a performance car, but it still is off the mark by 186lbs

A M3 will have an even shorter wheelbase than either Teslas thus far, or an F-150 for that matter. So the weight distribution will be even more important for vehicle dynamics under regen. I drive a manual for about 30k miles a year and put in about 5 races in a small formula car every year, I know about downshifting, engine braking, and most importantly, not upsetting car balance in the middle of a turn...because I learned the hard way into a few gravel traps. Coasting is taken for granted by most all drivers on the road and often in cornering situations it is the safest power option once you have already turned in - having to hunt for the point on one pedal knowing that if you just let go of it you will go into regen is neither intuitive for the average street driver not efficient in any performance situation.

I do not doubt that some on here have mastered this process on their Model S; however, Tesla is stepping up to a mass market car and in doing so needs to create the lowest bar for entry into the EV market, they have done it on price and they should also do it IRT control.

Lastly I agree with, what appears to be the preponderance of sentiment on this thread outside the hardliners, that the amount of regen should be fully configurable on both pedals. As it is a matter of software I see no reason why this should not be implemented.

 

[Az_Rael]

Do you have difficulty gauging the how far the car will travel on an incline when you take your foot off the go pedal ?

Honest question -- I'm trying to understand.

I view regen that way, as an additional slowing force on the car. If it is not enough, I add more by using the brakes. <<shrug>>

Otoh, I've watched my wife drive and she coasts very, very little. It will be interesting to see if she has difficulties with the Tesla.

Well, I don't live near many inclines steep enough to slow the car as much as regen does, so I guess I don't know the answer to that. (Edit: I do live near mountains, but only have to drive in them occasionally)


As far as why I personally have trouble with learning the regen - its mostly about my tendency to lift my foot off the accelerator very quickly to cover the brake whenever I see anything fishy happening on the road up ahead. I am a very conservative driver, so that happens to me a lot when other people get crazy here on LA roads.

Also - the majority of my driving is highway on cruise. I used to turn off my cruise control by tapping the brake pedal - THAT habit makes for a very jarring transition. And learning how to come off of cruise gracefully with heavy regen is tough sometimes - you have to gauge how much to push the accelerator down before you disengage cruise, all while you are traveling towards something that requires you to slow down.



Overall, I am treating it like when I drove a manual. The benefits are great - its tons of fun to feel like you are "one" with the car as you row through the gears accelerating. But there are sometimes when it sucks - stop and go traffic and steep hill starts on crowded roads come to mind. I actually bought my first automatic when my drive consisted of a daily slog through 20 minutes of stop and go traffic. Got tired of the hassle and sold the manual. (Wished I had kept it later when I moved to CA with lots of lovely canyon roads and no stop and go on my commute, LOL)

 

[SageBrush]

As far as why I personally have trouble with learning the regen - its mostly about my tendency to lift my foot off the accelerator very quickly to cover the brake whenever I see anything fishy happening on the road up ahead.

Ah .. that makes sense. My wife acts the same.

Heavy regen then might be exactly what you two need then: the car slowing down while you decide whether it is safe to advance.

 

[SageBrush]

often in cornering situations it is the safest power option once you have already turned in - having to hunt for the point on one pedal knowing that if you just let go of it you will go into regen is neither intuitive for the average street driver not efficient in any performance situation.

I don't have any understanding of the mechanics of cornering, but I do know that I apply light acceleration and continue to gently turn into the corner. This has always 'felt' right -- for what that is worth LOL

 

[trils0n]

I don't have any understanding of the mechanics of cornering, but I do know that I apply light acceleration and continue to gently turn into the corner. This has always 'felt' right -- for what that is worth LOL

Most people seem ride their brakes through corners or turns. It isn't a problem to regen or accelerate a little bit in a corner as you've noticed. You can even fly into a 25mph on-ramp at 50mph, completely lift on the accelerator for max regen and turn, and guess what, nothing bad will happen, despite posters trying to claim it is a problem. The car simply slows down and you make your turn, be it a little faster than is comfortable for most. The accelerator / regen is tuned in such a way that it is really difficult to kill yourself, even if you do things that aren't the brightest (like going way too fast into a corner and lifting off the accelerator).

As to the the posters claiming it won't be intuitive for new / mainstream car buyers, that is probably pretty far from the truth. Model S is an extremely easy car to drive, and very intuitive, so I expect Model 3 will be almost exactly the same in that regard. If you want to maintain a neutral throttle through corners it is fairly easy to do, no "hunting" required.

 

[Dan Detweiler]

It's not difficult, just takes some getting used to. My brakes on the Volt look new after four years of driving.

Dan

 

[Craig9080]

I don't have any understanding of the mechanics of cornering, but I do know that I apply light acceleration and continue to gently turn into the corner. This has always 'felt' right -- for what that is worth LOL

Then you are doing it right! Slowish in faster out; however, as a few posts after yours pointed out, most people don't do that but instead brake in the turns. 90-95% of the time it wont bite you. Some of that is due to ESC and some of that is due to good modern tires. It seems that the more drivers forget the basic physics of driving, the better engineers making the cars seem to get at making these cars idiot proof.

 

[proven]

According to Tesla, the Model S has a 48% front 52% rear weight distribution, it is a reverse pendulum-but not much of one. An F-150 has a heavy engine up front, a large cabin, and then an empty box at the back. I could not find anything on it's weight distribution (because no one cares about that for a truck) but it is definitely front heavy when unloaded. An F-150 will default to under-steer in limit handling situations due to the weight distribution and even in the event of power over-steer (assuming you are actually traveling forward and not trying to do donuts) the large amount of weight up front and the lengthy wheelbase will help fight the effects of over-steer.

The Model S will have a tendency to rotate under rear slip events either under power, braking, or regen due to the ~186lb weight imbalance to the rear. Again, this is actually not a bad weight distro for a performance car, but it still is off the mark by 186lbs

A M3 will have an even shorter wheelbase than either Teslas thus far, or an F-150 for that matter. So the weight distribution will be even more important for vehicle dynamics under regen. I drive a manual for about 30k miles a year and put in about 5 races in a small formula car every year, I know about downshifting, engine braking, and most importantly, not upsetting car balance in the middle of a turn...because I learned the hard way into a few gravel traps. Coasting is taken for granted by most all drivers on the road and often in cornering situations it is the safest power option once you have already turned in - having to hunt for the point on one pedal knowing that if you just let go of it you will go into regen is neither intuitive for the average street driver not efficient in any performance situation.

I do not doubt that some on here have mastered this process on their Model S; however, Tesla is stepping up to a mass market car and in doing so needs to create the lowest bar for entry into the EV market, they have done it on price and they should also do it IRT control.

Lastly I agree with, what appears to be the preponderance of sentiment on this thread outside the hardliners, that the amount of regen should be fully configurable on both pedals. As it is a matter of software I see no reason why this should not be implemented.

I'm curious if you've been for a test drive yet in a Model S? The pedal has been designed and tuned so well that it's extremely easy to "master" the amount of pressure you need to do anything. My wife and I both effortlessly drive around town with hardly using the brake pedal... In fact we get frustrated when we misjudge something and have to brake. I really think people should give it a try before asking for regen on the brake pedal.

 

[The Lorax]

I'm curious if you've been for a test drive yet in a Model S? The pedal has been designed and tuned so well that it's extremely easy to "master" the amount of pressure you need to do anything. My wife and I both effortlessly drive around town with hardly using the brake pedal... In fact we get frustrated when we misjudge something and have to brake. I really think people should give it a try before asking for regen on the brake pedal.

Totally agree with this. It takes all but a few days to get used to and once your are used to it, you wouldn't want it any other way.

 

[SDRick]

[QUOTE
="JeffK, post: 1551510, member: 47515"]I have to be honest I'm going to get a Tesla purely for the acceleration and the regen. I LOVE engine braking and horribly miss having a manual transmission.

Even though there's only one gear I want the Tesla to behave exactly like a manual in low gear. It's a ton of fun on winding roads.[/QUOTE]

My feelings exactly. I think the execution of standard regen is perfect. One petal driving is my preference and superior to going back and forth between the brake and the "gas"!

 

[Craig9080]

I'm curious if you've been for a test drive yet in a Model S? The pedal has been designed and tuned so well that it's extremely easy to "master" the amount of pressure you need to do anything. My wife and I both effortlessly drive around town with hardly using the brake pedal... In fact we get frustrated when we misjudge something and have to brake. I really think people should give it a try before asking for regen on the brake pedal.

I have infact, at the Decatur location in ATL. It is the best car I have ever driven, I actually feel let down by my DD after doing so. That being said, I loved the one pedal solution when I was putsing around town or on the highway, but when I grabbed a big bunch of "go" in an off-ramp I was oddly unsettled by mid-tern modulation. As a [crappy] racing enthusiast, I have learned how to stay out of the wall and the way it behaved would have me pulling into the pits if I was on a track - simply put, I would have rather put it on jack stands than laped it. I plan to flog the crap out of my model 3. Track days, time trials, autoX (lol), and anything else I can throw at it. I beg Tesla go just give me an option to tune it to they way I want.

 

[jdbob]

I currently have a C-Max Energi (I'm in the uncharged territories, hoping to have charging infrastructure by 2020) and I think the blended brakes work just fine. After all, except for emergencies when there is a mechanical override, you are just pushing on a pedal that feeds a voltage into a computer. The computer decides how to allocate between regeneration, front disk, and rear disk brakes.

Maybe the cars where people thought the blended brakes sucked use some sort of mechanical blending?

 

[proven]

I have infact, at the Decatur location in ATL. It is the best car I have ever driven, I actually feel let down by my DD after doing so. That being said, I loved the one pedal solution when I was putsing around town or on the highway, but when I grabbed a big bunch of "go" in an off-ramp I was oddly unsettled by mid-tern modulation. As a [crappy] racing enthusiast, I have learned how to stay out of the wall and the way it behaved would have me pulling into the pits if I was on a track - simply put, I would have rather put it on jack stands than laped it. I plan to flog the crap out of my model 3. Track days, time trials, autoX (lol), and anything else I can throw at it. I beg Tesla go just give me an option to tune it to they way I want.

I understand your situation would make sense to be able to tune it... but this is far from a track car, it's a small sedan--maybe you should get a roadster or wait until roadster 2.0 to do some racing?

 

[Craig9080]

I understand your situation would make sense to be able to tune it... but this is far from a track car, it's a small sedan--maybe you should get a roadster or wait until roadster 2.0 to do some racing?

I love the thought, but a roadster is just out of my price range. I have been a fan ever since the Top Gear UK episode and I hope to own one someday when I'm a few rungs higher on the ladder. I'll have fingers crossed that they make it adjustable.

 

[Red Sage]

...Tesla is stepping up to a mass market car and in doing so needs to create the lowest bar for entry into the EV market...

I'm not exactly a proponent of 'least common denominator' thinking. Here, take a look at this video. Right around the 10:28 mark, they talk about Regen.

 

[Luke42]

Regen does not upset the dynamic response of the car because it is done at relatively low deceleration rates (less than 0.3g).

You've clearly never driven on ice.

0.3Gs is probably at lrast 10x the amount of acceleration yiu can get from the traction that's available.

The easiest way to regain control of the car on ice is to cut power to the wheels and point the front wheels to match the direction of travel.

Back when I had a manual, the quickest way to cut power and regain control was to mash the clutch, steer, and then *very* gently brake.

The TCS/ABS on the Prius was pretty good at detecting wheel slip and reducing lower to the wheel in question.

Hopefully the TCS/ABS on the Model 3 is pretty good, too. I've already bet my $1K that it will be pretty good.

But, 0.3Gs of attempted regen on ice will turn any vehicle into a hockey puck. An uncontrolled slide is an enormous degredation of driving dynamics.


P.S. Lots of people are unprepared for this degradation in controlability, even here where it happens every year and learning to deal with it is just part of learning to drive. You've really gotta watch for people sliding through stopsigns and traffic lights during the first slippery day of every winter. And that's *WITH* ABS being effectively mandatory on all cars made in the last couple of decades. You can barely feel the acceleration/deceleration/turning force that you can get on the worst kinds of ice. It's not enough acceleration to slosh coffee, so it's a small fraction of 0.3G.

 

[Luke42]

Fair enough, since the OP's thesis is based on the Model S I forgot this was in the M3 forum. It is good however that you hear from the people who actually drive the cars on a daily basis.

Yes, but there's no reason to be condescending about it.

That sarcastic comment upthread about "oh, another non Tesla owner weighs in" is the most condescending thing I've seen on this forum since I put down my deposit. That kind of attitude soured the BMW brand for me, first in traffic and then on the Internet.

Its much better to actually explain your experience.

 

[JeffK]

You've clearly never driven on ice.

Driving on ice in a Tesla is very different than driving on ice in a Prius. The Prius (at least my gen II) has extremely poor traction control. It's version of traction control is shutting off all engine power while your foot is on the gas for nearly a second at a time when it detects wheel slip. This can lead to very dangerous situations in winter weather such as when crossing a lane when turning etc.

When you say the Prius is pretty good at detecting wheel slip and reduces power to the wheel in question, I have to say it certainly does not work that was in my Prius, it cuts power to ALL wheels for an absurdly long time making it effectively an accident waiting to happen.

A Tesla on the other hand is much smarter about it and can make adjustments a heck of lot faster...

I cannot wait to get out of my Prius into a Model 3. I'd feel MUCH safer.

 

[colettimj]

Before anti-lock brakes, you learned to pump your brakes during emergency braking to avoid losing control of the vehicle. With anti-lock, pumping the brakes is the wrong thing to do. For regen on the accelerator, you now need to maintain some pressure on the pedal to coast otherwise the car is decelerating. I think you'd just need a bit of time to adapt to a new way of driving.

I also think it is an advantage that, in a braking situation, a Tesla is already starts slowing you down significantly as soon as you release the accelerator; a fraction of a second before your foot starts depressing the brake pedal.

I guess I don't understand why this is an issue.