Why regenerative braking belongs on the brake pedal

[Zoomit]

If, perhaps the battery tech changes, and more regen becomes possible because the battery can take more and stronger regen elec, then perhaps Tesla could decide that anymore decel from the accel pedal would be too much (e.g., the car would come to a screeching halt) and then they could put that excess regen on the brake pedal. But that may never happen in short term due to current battery tech.

I wonder if on a model 3, because it is lighter, and perhaps because of battery tech improvements, the full regen could be so strong, that they might allocate some of it to the brake pedal input -- the issue is how strong of the decel feels best on the accel pedal? Maybe the current -.3gs is best? Maybe up to -.5gs? Most current Tesla drivers feel that even more than what is currently available would be preferable, so maybe a Model 3 that has even more will feel even better and won't have to allocate any to the brake pedal.

Why do you think the battery is the limiting factor on regen power?

A Spark EV, which only has an 18 kWh battery, can also collect 60 kW via regen.

 

[deonb]

Wait, seriously? If you push the car off a cliff (which is what you did with that calculator, it computes terminal velocity of an object falling straight down) then regen is going to be nil anyway, because you're not going to get enough traction on the cliff face to spin the axle. However, there is a terminal velocity for every other slope other than a 90° one too <snip>

My reply was to a hypothetical scenario of falling at terminal velocity where "all of the energy is going into drag":

When you fall at terminal velocity, all the energy you are gaining is going into drag

There is only 1 scenario & speed at which all energy is going into drag, and that's a straight-line fall, which at nose-first would have a terminal velocity of 486mph.

When you're at another angle against a slope etc. it's other types of frictions that take over (regen being one of them) - not just drag.

 

[bhzmark]

Why do you think the battery is the limiting factor on regen power?

A Spark EV, which only has an 18 kWh battery, can also collect 60 kW via regen.

I'm not sure of that -- just something I read on the internet. And supercharger charge at much more, but I recall someone explaining plausibly that the type of recharge from the motor in regen mode is limited both at max capacity and at low speeds (hence why we lose regen at <5 mph).

If that were overcome, and after some additional regen braking were added to accel pedal up to a limit that was a good balance of strong braking, but not a screeching halt, and there were a way to move the rest of the battery regen capacity to make electricity instead of making brake dust, I would be in favor of that.

 

[jgs]

My reply was to a hypothetical scenario of falling at terminal velocity where "all of the energy is going into drag"
[...]
There is only 1 scenario & speed at which all energy is going into drag, and that's a straight-line fall, which at nose-first would have a terminal velocity of 486mph.

When you're at another angle against a slope etc. it's other types of frictions that take over (regen being one of them) - not just drag.

I see, OK. Seems a bit nit-picky to me -- when I read @ThosEM's post I mentally interpolated "frictional forces" for "drag" without even considering it. His argument stands if you do that.

Also, if we're going to pick nits, I think it's a reach to classify regen under "other types of frictions" unless you're going to broaden "friction" all the way out to "things that slow you down" instead of the usual "force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other". Regen doesn't even fall into the category of "losses" as friction does, since the whole point is that it's not all lost when you regen.

Does this mean you aren't going to trade me your car for an equivalent-shaped dead weight?

 

[deonb]

Does this mean you aren't going to trade me your car for an equivalent-shaped dead weight?

I would be happy to trade you for an equivalently shape & mass of dead weight. As long as I can choose the metal that said dead weight consists of .

 

[Tiberius]

Please let this thread die

 

[ThosEM]

I would rather have lift off regen than brake based. I was just curious how much hardware change is required if Tesla were to have free cycles (hah) to allow blended brakes.

Note to Tesla! I do not support you spending a single free cycle trying to blend brakes and regen. Blended brakes suck! I have owned a Lexus hybrid and I will never again buy any car that forces me to deal with "blended brakes". If you put them in, you'd better provide a switch to turn them off.

 

[jgs]

Please let this thread die

You'll find an "Unwatch Thread" link in the upper right-hand corner (or so).

 

[GeekGirls]

I understand that regen on the throttle is initially disconcerting for many, but I grew to appreciate it very quickly. How many who have owned a Tesla for a year or more and care about efficiency actually leave theirs set to light regen? Our Model S and i3 both offer aggressive regen and my wife and I both really appreciate that design philosophy.

It's safer, because the vehicle starts to slow aggressively long before you touch the brake pedal. It's efficient. You learn quickly enough how to coast effectively and our efficiency stats are better than EPA ratings. It's also mechanically simple where it counts: braking in an EV is something you do when you have to, not a routine operation.

 

[MitchMitch]

Not to hijack 229 posts, but talk of calculators a few pages back got me thinking about an HP vs TI debate clear back in the 1970's. (insert image of geeks fist-fighting here) Having originally been a TI guy, I was a tough convert to the HP (engineers' ?) method. The efficiency required attaining a certain measure of finesse... not always an easy or quick process.

Google

The elegance of one-foot driving will eventually win-over all but the unwilling.

 

[Craig9080]

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.

Lol, I point out that you need to use science when arguing so instead of providing a counter point people just dislike my post.
Translation:
"1+1=7"
"I apologize but it does not, can you tell me why 1+1=7?"
"I don't like you"

 

[Xminus6]

I'm going to start a petition to get all audio equipment manufacturers to split the dual-purpose volume dial into two distinct dials. I want one that only turns the volume up and a completely separate knob to turn the volume down. Those of you who disagree are wrong.

 

[SageBrush]

I'm going to start a petition to get all audio equipment manufacturers to split the dual-purpose volume dial into two distinct dials. I want one that only turns the volume up and a completely separate knob to turn the volume down. Those of you who disagree are wrong.

I have that on my aftermarket car play display. Lucky, lucky me, one button for volume up and another for volume down.

It sucks

 

[bhzmark]

Note to Tesla! I do not support you spending a single free cycle trying to blend brakes and regen. Blended brakes suck! I have owned a Lexus hybrid and I will never again buy any car that forces me to deal with "blended brakes". If you put them in, you'd better provide a switch to turn them off.

Yes, because if toyota couldn't do it on my 2005 prius, tesla won't be able to do it.

Tesla cant do anything that other companies can't do.

 

[ThosEM]

Please let this thread die

We don't deserve to have this much fun?

 

[ThosEM]

Yes, because if toyota couldn't do it on my 2005 prius, tesla won't be able to do it.
Tesla cant do anything that other companies can't do.

Tesla is smart enough not to do many of the things other companies do. But hey, I conceded up front this is a matter of taste. I like Tesla's taste, so far...

 

[ThosEM]

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

This calculator tells me it's 486 mph:

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.

Here's an undeserved straight response to a sarcastic comment:

A car losing altitude reaches terminal velocity by definition, when it no longer speeds up. That depends on how steep and long the hill is, up to and including the straight down drop, which is obviously undesirable but can happen inadvertently if one is not careful.

My point was that for a typical highway incline, the car reaches terminal velocity rather early in the descent and from there on all the potential energy gained is being dissipated as friction of various types, dominantly aerodynamic drag at higher speeds.

If instead, the speed is held below terminal speed by regeneration, excess potential energy not being used to maintain speed flows back into the battery (or warms up the inverter). Again, it depends on slope of the incline, that is, the amount by which the power derived from the descent exceeds that needed to push the car forward through the air. No one is advocating use of regen to slow down when descending hills; only that it be used to avoid speeding up.

Quibbling about the efficiency of regeneration does not change the conclusion. However, some of the folks who claim low regeneration efficiency also claim that electric motors are 90% efficient. So maybe they can explain why they are so much less efficient as generators than as motors?

Regeneration is your friend, and it is not more energy efficient to put your car in neutral (literally or virtually) and coast wildly down hills at whatever terminal speed results. People build and drive hybrids mainly for the advantage yielded by regenerative braking. Why wouldn't you use it in a pure EV?

 

[Rocky_H]

I want to thank @JeffC for this thread. It has been wonderfully entertaining. Some of my favorite bits were these:

Quote: "I'm a libertarian. I'm in favor of freedom."
vs.
Quote: "heavy regen on throttle is a poor idea that should be banished."

Ha ha, that's some awesome "freedom" there.

And then the whole section on ergonomics was nothing but opinion and preference, couched as scientific fact. This line especially was hilarious:

Quote: "it cross couples braking control with acceleration control. These are separate functions, and the controls should reflect that."

Well, one might possibly say that controlling one's speed is a single function, and the controls should reflect that. There's really not any difference at all between applying these same arguments to the idea that turning left versus turning right are two different functions, or steering being considered one function. Either way can work, and it's just preference.

Also, when purporting to be all scientific and stuff, you should probably avoid giving away your bias with such mean-spirited and emotionally attacking phrases such as "groupthink" and "emperor's new clothes".

 

[Electricfan]

One pedal driving RULES!

I'll live with the oversteer (which I've never felt).

 

[F_T_K]

I'm currently driving a Prius, and I like how it handles the regen. Taking my foot off the gas allows some coasting, some light regen, and a chance to relax my leg. If I want a little more regen, a very light touch on the brake pedal accomplishes that, without engaging the physical brakes.

I would hope my Model 3 allows a similar setup.