Why regenerative braking belongs on the brake pedal

[JeffK]

Some people missed the bit of the discussion where the premise was not to increase in speed while coasting... down a large hill this is not possible as Topher ended up finally saying. People either brake or regen. Regen is better in this case... Yay, we all agree.

But let's get back to the original post where we all agree regen is awesome on the accelerator and one and a half persons say it's better on the brake for some odd reason.

 

[deonb]

Some people missed the bit of the discussion where the premise was not to increase in speed while coasting...

We must have. (Otherwise we would have pointed out the ridiculous premise). So would you be so kind as to link to that?

 

[JeffK]

We must have. (Otherwise we would have pointed out the ridiculous premise). So would you be so kind as to link to that?

I quoted it more than once but it's here
Why regenerative braking belongs on the brake pedal

I get what Topher was trying to say with regards to the post he was responding to... assuming there's a next hill. The poster Topher was responding to was incorrect about his assumption.

We quite literally hijacked this thread so I'm going to say no more about regen vs coasting except that any sane person would use them in different situations where appropriate.

(drops the mic)

 

[deonb]

I quoted it more than once but it's here
Why regenerative braking belongs on the brake pedal

I get what Topher was trying to say with regards to the post he was responding to... assuming there's a next hill. The poster Topher was responding to was incorrect about his assumption.

Yeah, ok. Both those statements were erroneous. ThosEm because of bad math, Topher because of bad grammar. Either way, enough has been said on the topic.

We quite literally hijacked this thread

I think we're all just waiting for JeffC to step back in and say something silly again that only the mother of a true non-Tesla owner can love.

Until then we're just biding time.

 

[Red Sage]

I wrote, "From some of your replies to others here, I get the impression that you want Tesla Motors vehicles to drive more like machines, and less like appliances. Is that a fair assessment?"

Not really sure what that means, TBH.

Others have lamented one-foot driving before. Typically it is because they have spent years perfecting heel-n-toe driving of manual transmission vehicles. They prefer three pedals on the floor, a stick in their hand, a handbrake within easy reach, and immediate, darting steering actions that require naught more than a flick of the wrist to correct course. They don't want to drive a car, they want to operate a machine. The more things they can do at once to coax a vehicle into submission the more 'manly' they feel. The more knobs, dials, cranks, ratchets, levers, pedals, and wheels they have to juggle, the happier they are... Y'know, sort of like Doctor Who in a steampunk TARDIS.

I'd like the regenerative braking to be integrated with the friction brakes on the brake pedal.

Yeah, but... WHY? How will that improve the driving experience?

Everything else about the Tesla driving experience is very good. They're very clearly designed to be driver's cars. They have great suspensions, outstanding handling for such heavy, large cars, good control feel, pretty good sight lines, etc.

First and foremost, Tesla's are outstanding driver's cars. That they can also drive themselves like appliances, is an added benefit. And they really maximized the potential of EVs in making a great driver's car.

Cool. But once you know all that is true... Why the need to [FOUL] it up by making a fundamental change to it?

 

[roblab]

It always interests me how people will form an opinion and then insist that other people do it according to what they have decided. Many threads here have someone who turns out to not even ever have driven a Tesla decide on how Tesla should have done something.

I have driven several electrics, for the past 15 years or so, and I think (my opinion) that in everything I have come across, Tesla has done it right.

If someone thinks they haven't, or if someone doesn't like it, hey, go somewhere else. That's competition.

 

[SageBrush]

I think most of us can agree that there is a point where drag forces are higher than conversion losses. Rather than set up an equation I spreadsheeted (that is a new verb) the case of a car I deem the M3, and compared 80 vs 81 mph:

Let's call the increased drag 500 watts, and say that ~ half of the KE between 80 and 81 mph can be regen'd, so ~ 15,000 watt-seconds.
If we bleed off the speed in less than 30 seconds, momentum over regen is preferred. The time is actually quite a bit longer than 30 seconds but let's go with that.

ONE mph in 30 seconds ... Yeah, I can do that.
In fact, there are about 20 kW of road and aero acting against the car at that speed so on level ground it will take around 1.5 seconds to bleed off the speed ...

750 w*sec wasted on Aero drag. And yes, it is not a complete analysis. But the numbers are so wide apart that the opposing viewpoint is starting from a huge disadvantage.

 

[S100D]

Tesla got it wrong when they put heavy regen on the throttle. It's one of several things they got wrong, but probably the most serious one. It's not stopping me for buying a Tesla or two, but worth pointing out. When I test drove a Model S, I liked it much better with Low Regen. I realize I'm probably in the minority on that, but I also realize most people are very likely ignorant about the reasons why.

Also be aware that Tesla itself is not monolithic on the issue. There are engineers inside Tesla who agree that regen belongs on the brake pedal, not the throttle.

Please educate yourself first before commenting.

Flames to /dev/null

Jeff, you are entitled to believe what you want but Tesla got the regen 100% correct. I would recommend that you cancel your Model 3 order and buy a Lexus 300h which has regen on the brake pedal.

I owned a 2014 Lexus 300h and the Tesla regen eliminates the need for me to take my foot off the accelerator and press the brake to get regen. It also reduces brake pad and rotor wear. In case you do not know, yes the brake lights come on when you are in regen.

Since you do not own a Tesla, it is hard for me to believe that you know any Tesla engineers that agree with you.

I do agree that you are in the minority, I think you may be the only person in the Universe that believes regen belongs on the brake pedal.

 

[Zoomit]

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.

My qualifier was that the traditional 2-pedal way wasn't necessarily the best. But two pedals are definitely needed. Using two pedals with different accel/decel mapping like Tesla does is better and having a means of applying full brake force in a second pedal makes sense to me. Engineers would never be able to use just one pedal because the car cannot go into full braking if the driver inadvertently removes their foot from the right pedal.

 

[SageBrush]

With all due respect, I think I am the minority here because I am happy either way.

Fwiw though, all automatic gearing cars I can think of slow down when the foot is completely taken off the pedal, so regen on the go pedal is just the same or more of the same thing.

Want even more 'slowing' ? Hit the brake

Want to coast ? Tap the 'go' pedal lightly in either car.

 

[FlatSix911]

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.

Race car drivers use both the Transmission and the Brakes to decelerate and stay in the optimum ICE power band.
For the average Joe, downshifting can lead to expensive repairs...YMMV
We have saying at the track ... Brake pads are cheap, Transmissions are not

 

[ohmman]

When I drive Trinity Road between Sonoma Valley and Napa Valley, I'm able to make it most of the way without touching the brake pedal. On a road with a lot of cyclists, that eliminates a significant amount of time that my foot isn't touching either pedal (during the transition). I don't know what it means for safety, but it seems better and it certainly feels more natural. This is the kind of mountain road that is perfect for single pedal driving.

 

[Lon12]

JeffC, I found your essay to be.... well kind of insulting to many of us on this forum.
"A majority of Tesla drivers may disagree with the above, but most of their experience will be informed by a very limited set of driving experiences typical of most street use, and not racing, limit behaviors or emergency maneuvers. They may like the emperor's new clothes, blissfully thinking the new "clothes" are really cool, when in fact they're a naked ergonomic error."

You have no idea how many of us do race on a regular basis and aren't "blissfully" doing anything of the sort.
I've learned a lot from driving the Model S in snow and ice. I tried very hard to get it to misbehave. I also track race regularly and am very familiar with everything you mention in your essay.
Previously I drove brake pedal regen on my hybrid vehicles for over 10 years. I had the same concerns that you have after I started driving the MS. After seven months of driving I would say that I now prefer single pedal driving over anything else. Most of the reasons have already been posted in this thread so I will not repeat them. But one of my favourite is the ability to quickly check your traction level by simply lifting the accelerator. On ice in an "ICE" I would press the brake pedal and have to listen to the whole anti skid system complain and scare everyone in the car. With the MS a simple lift on the accelerator is all you need to feel the slip and know whats under you. Awesome!

 

[EV-lutioin]

On a thread about the Leaf, there was a complaint that Nissan got it wrong then they had the default regen setting when coming off the throttle to be very light regen. Actually that is the correct way to do things for several reasons. Reasons which non-automotive engineers and non-racing drivers generally would not be aware of. Most of the regen is done on the brake pedal on the Leaf, Volt, EV1, Toyota RAV4 EV (the original one made by Toyota, not Tesla), Prius, VW e-Golf and many other EVs and hybrids. Read some of the history in my link below.

Tesla got it wrong when they put heavy regen on the throttle. It's one of several things they got wrong, but probably the most serious one. It's not stopping me for buying a Tesla or two, but worth pointing out. When I test drove a Model S, I liked it much better with Low Regen. I realize I'm probably in the minority on that, but I also realize most people are very likely ignorant about the reasons why.

Please read and learn: Why Regenerative Braking Belongs... On The Brake Pedal

Also be aware that Tesla itself is not monolithic on the issue. There are engineers inside Tesla who agree that regen belongs on the brake pedal, not the throttle.

Please educate yourself first before commenting.

Flames to /dev/null

Too funny, one of my favorite things about my Tesla is the regenerative braking, it allows for a perfectly smooth transition from acceleration to deceleration, no more hurky jerky ICE driving. When you master it you can almost never use your brakes.... it's magical!!

 

[SageBrush]

Even presuming that the race track arguments are correct, It strikes me as more than a little hare-brained to expect Tesla to engineer by them. The car is a road car.

 

[diamond.g]

Is it possible for Tesla to even offer the option of blended brakes without actually changing the braking hardware?

 

[bhzmark]

Is it possible for Tesla to even offer the option of blended brakes without actually changing the braking hardware?

I think the Bosch iboosters used by Tesla since the AP update are used in other cars that use the brake pedals for regen.

But the point is that I believe the full regen the battery is capable of (about 60kw) is already built into the accel pedal lift off. So since everyone who actually owns and regularly drives a Tesla prefers the full regen that the car is capable of (which is limited, I think to about -.3gs) to be on the accel pedal, there is no more regen to be had from the brake pedal.

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.

 

[diamond.g]

I think the Bosch iboosters used by Tesla since the AP update are used in other cars that use the brake pedals for regen.

But the point is that I believe the full regen the battery is capable of (about 60kw) is already built into the accel pedal lift off. So since everyone who actually owns and regularly drives a Tesla prefers the full regen that the car is capable of (which is limited, I think to about -.3gs) to be on the accel pedal, there is no more regen to be had from the brake pedal.

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.

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.

 

[jgs]

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

This calculator tells me it's 486 mph

[and so on]

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. On a 0° slope (i.e., on the flat) it's zero. Your calculator gave you the other extreme. Any other hill is somewhere in between. Since terminal velocity varies continuously between zero and (you tell us) 486, it's obvious by inspection that there must be some slope for which terminal velocity is 75. This is also intuitively obvious because if you've ever gone down a hill where you had to use the go pedal to hold your speed, terminal velocity on that hill was lower than your speed. And top speed of any car is lower than 486.

By the way, if you do want to push your car off a cliff to test your theory, please let me know and I'll supply a stand-in of equal mass and Cd in trade for your car.

 

[jgs]

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.

In AP models, probably no HW change.