Why regenerative braking belongs on the brake pedal

[deonb]

I am blown away buy the amount of arrogant and willfully ignorant hate over a guy pointing out the practical effects of regen on the throttle. If your "rebuttal" doesn't include an empirical rebuke of the science at hand, the it holds no relevance but feel free to exercise your freedom of speech...if you live in the USA...because Canada doesn't have that.

Because the "science at hand" amounts to: "I don't have a Tesla. I haven't spoken to Tesla owners. I haven't done a study on the safety aspects of this, nor have I found a single anecdotal case of this being a problem ever. But I test-drove a Tesla once and it seemed strange, so a couple of buddies and I got together over a few beers and decided it's time Tesla changes this for everybody."

You can imagine that not being a popular opinion.

 

[Zoomit]

Why won't this thread die?

This discussion is just a prelude, a warm up, for late 2017.

 

[deonb]

Two vehicles go down a hill and maintain constant velocity of 75mph, one is using regen to maintain 75mph the other is coasting to maintain 75mph. Both get to the bottom of the hill and are on flat road still doing 75mph (same kinetic energy at this point).

Sigh. That's not the real case. The real case is:

2 vehicles go down a hill, starting at 50mph. One uses regen to maintain 50mph down the hill, and one uses coasting and accelerates and hits 75mph at the bottom of the hill

At the bottom of the hill the road turns straight (or uphill). The car that regen'd uses battery and stays at 50mph until the amount of regen he put into the battery is used up, and the car that was at 75mph coasts until he is back down to 50mph.

Which one goes further? Evidence so far says the car that coasts would go further, until the point where the speed exceeds 75mph, in which case aerodynamic losses causes the balance to shift the other way around.

 

[Zoomit]

Well argued by the original author but the "appeal to nature" argument has no validity - there is nothing that's more or less natural about having regen on lift off of accelerator or on the brake pedal. It's all convention (which mustn't be confused with "naturality". There's nothing "natural" about cars anyway).

The appeal to safety argument is clearly wrong since millions of Tesla miles driven disproves the way Tesla implementing regen being dangerous.

The appeal to efficiency/coasting argument has some merit but is probably for the vast majority outweighed by the convenience of one foot driving.

The rest is, as they say, purely subjective that is no right or wrong answer.

Good points, but there absolutely can be wrong human-machine interface design.

The classic 2-pedal system predates the entire field of human factors engineering. I see no reason why a clean sheet vehicle interface design would come up with two pedals, one only modulating deceleration power and the other only modulating acceleration power, as the preferred solution. Actually, I can and that's only to maintain conformity with past designs or habits.

 

[SageBrush]

^^ This
Convention != Natural. It just implies ingrained habit

 

[Kipernicus]

For the record, I like one-pedal driving and how Tesla implemented the regen. I have gotten used to adjusting the pedal to 0kW to coast.

BUT, there have been times where I felt my leg muscles getting tired of holding that precise position for a long time, whether it is a long slope, trying to hypermile, or just trying to drive smoothly with few/gradual transitions between acceleration and regen.
Also, when switching off cruise control one has to remember to depress the accelerator to avoid the sudden lurch of regen.

I'm in a gasser for the next week and a half (thanks to Burlingame service being so overloaded but that's a story for another thread), and it certainly takes less mental and physical effort to not have to hold the accelerator just so.

 

[int32_t]

... If you read my essay, a significant number of the engineers inside Tesla feel that way too.

Yeah, but that data seems to come from Roadster / pre-Model S days. I'd be curious what a vote would come to now.

Okay. Let me argue that single-pedal driving is safer than two-pedal driving. In those corner cases where every tenth of a second counts, you can save three tenths of a second by having regen slow your vehicle as your foot comes off the go pedal even before you an hit the brake. I'd guess the vehicle would stop shorter, especially from a high speed where everything counts.

-- Updated --

Seems that somebody else got to my second point first. I got bored and skipped a few pages ...

 

[mrElbe]

Sigh. That's not the real case. The real case is:

2 vehicles go down a hill, starting at 50mph. One uses regen to maintain 50mph down the hill, and one uses coasting and accelerates and hits 75mph at the bottom of the hill

At the bottom of the hill the road turns straight (or uphill). The car that regen'd uses battery and stays at 50mph until the amount of regen he put into the battery is used up, and the car that was at 75mph coasts until he is back down to 50mph.

Which one goes further? Evidence so far says the car that coasts would go further, until the point where the speed exceeds 75mph, in which case aerodynamic losses causes the balance to shift the other way around.

True, but in real life there could be a 50mph speed limit and a state trooper lurking at the bottom of that hill. So the regen driver gains energy while the other driver constantly touches his brake pedal to maintain the 50mph speed limit.

 

[Topher]

Fair enough. The "evidence" I refer to its anecdotal and observational in nature without a proper control group. But non perfect data isn't always worthless. It's also appropriate to ask with who the burden of proof should lie: he who claims Tesla's implementation of regen is unsafe or he who claims it seems not unsafe?

The burden of proof always lies with the whomever is making a positive claim. You used the word "disproves" that is a pretty strong positive claim.

I seriously doubt that there is even enough data existent to differentiate. Teslas just don't have that many miles total driven.

Thank you kindly.

 

[int32_t]

... If braking hard in the middle of a turn can result in oversteer, then the same thing can happen from heavy regenerative braking...

My point (earlier post) was that it's not going to happen because of TC. Therefore it's moot -- a total non-issue. So if safety isn't the problem we're back to personal preference ... which is fine too, but don't expect to convince everyone. Evidence won't change preference; experience will. (Consequently most of us here seem to expect you to strongly prefer go-pedal regen if/when you drive a Tesla.)

 

[Topher]

Good points, but there absolutely can be wrong human-machine interface design.

The classic 2-pedal system predates the entire field of human factors engineering. I see no reason why a clean sheet vehicle interface design would come up with two pedals, one only modulating deceleration power and the other only modulating acceleration power, as the preferred solution. Actually, I can and that's only to maintain conformity with past designs or habits.

Ok, how exactly would that work? Letting off the gas completely applies emergency level braking? Relaxing leg muscles seems counter intuitive for an emergency situation.

[not mocking, honest question. I am blinded by a lifetime of driving the current way.]

Thank you kindly.

 

[deonb]

True, but in real life there could be a 50mph speed limit and a state trooper lurking at the bottom of that hill. So the regen driver gains energy while the other driver constantly touches his brake pedal to maintain the 50mph speed limit.

I am very happy to concede that regen is more efficient than braking. Absolutely. No contest. You win the internet. Great argument - wish I thought of that. JeffK will be happy to join you on another thread to discuss exactly that. I suspect it will be a short and/or lonely discussion since I don't know of anybody on the planet who disagrees with that.

Now can we stop bringing that up please. Saying that "sometimes people have to brake" doesn't detract from the argument that "when you don't have to brake, coasting is more efficient.".

 

[bhzmark]

For the record, I like one-pedal driving and how Tesla implemented the regen. I have gotten used to adjusting the pedal to 0kW to coast.

BUT, there have been times where I felt my leg muscles getting tired of holding that precise position for a long time, whether it is a long slope, trying to hypermile, or just trying to drive smoothly with few/gradual transitions between acceleration and regen.
Also, when switching off cruise control one has to remember to depress the accelerator to avoid the sudden lurch of regen.

I'm in a gasser for the next week and a half (thanks to Burlingame service being so overloaded but that's a story for another thread), and it certainly takes less mental and physical effort to not have to hold the accelerator just so.

Put it in neutral to coast. Very easy. Or just use tacc and dont worry about hypermiling like you used to do in your prius because elec is so cheap.

 

[int32_t]

[QUOTE="deonb, post: 1553340, member: 12703"... Now can we stop bringing that up please. Saying that "sometimes people have to brake" doesn't detract from the argument that "when you don't have to brake, coasting is more efficient.".[/QUOTE]
Zactly. When you don't have to brake, coast. If you have to brake, use regen.

 

[Snerruc]

I live on a mountain. I always downshift when going down grades. This creates a situation similar to regen on the accelerator. It is far easier to control a car in this case, especially as the roads are twisty and in poor condition. My friends have to replace brakes yearly and wonder why mine last for years. You actually can drive faster this way that is one reason race drivers drive with the gears. This is one reason I have a 3 reserved.

 

[ThosEM]

Sigh. That's not the real case. The real case is:

2 vehicles go down a hill, starting at 50mph. One uses regen to maintain 50mph down the hill, and one uses coasting and accelerates and hits 75mph at the bottom of the hill

At the bottom of the hill the road turns straight (or uphill). The car that regen'd uses battery and stays at 50mph until the amount of regen he put into the battery is used up, and the car that was at 75mph coasts until he is back down to 50mph.

Which one goes further? Evidence so far says the car that coasts would go further, until the point where the speed exceeds 75mph, in which case aerodynamic losses causes the balance to shift the other way around.

I know of no evidence for this to be true. Quite the contrary the car that captured energy in the battery will have about 90% of the energy it used to climb the hill back to work with on the rest of the trip, while the car that rolled free and speeded up to 75 will have lost most of that energy into drag resistance.

When you fall at terminal velocity, all the energy you are gaining is going into drag, the longer the car proceeds down the hill at its terminal velocity, the smaller the fraction of energy it captures as increased kinetic energy or speed.

 

[bhzmark]

Good to edit out the misinterpretation. And for speeds below 75 the drag loss is less than the battery loss.


Its amazing how hard it is too communicate accurately in this thread. Misinterpretation is evident in every other post.

 

[Jeff N]

the car that captured energy in the battery will have about 90% of the energy it used to climb the hill back to work,

The roundtrip efficiency of regenerated energy being saved and sent back to the wheels is typically reported to be closer to 60% on various cars and I have no reason to believe that the Model S is dramatically better.

 

[bhzmark]

This says 40%
Regenerative Energy - research paper

 

[deonb]

I know of no evidence for this to be true. Quite the contrary the car that captured energy in the battery will have about 90% of the energy it used to climb the hill back to work with on the rest of the trip, while the car that rolled free and speeded up to 75 will have lost most of that energy into drag resistance.

When you fall at terminal velocity, all the energy you are gaining is going into drag, the longer the car proceeds down the hill at its terminal velocity, the smaller the fraction of energy it captures as increased kinetic energy or speed.

The car's terminal velocity is not 75mph. It's far higher.

This calculator tells me it's 486 mph:
CalcTool: Terminal velocity calculator

I used a CS Area of 2.4 m2, because I know the Cd (0.24) and CdA (0.576m2) from here, and a CS Area of 2.4 gives me a CdA of 0.576.