Regen Braking for Beginners.... I have questions

[ajdelange]

Did you happen to notice / experience different levels of regen braking that the driver can adjust?

I'm not always certain that people understand this but in a pure one pedal system you have complete control over the level of regenerative braking from full on to full off. The only thing you lose is the ability to apply friction braking without any regen. I bolded "you" because the computer does not lose that ability. Thus if you slam on the friction brake and start to skid the computer will simply (well it's not really that simple) reduce or increase torque electrically to whichever motor(s) require it.

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[DucRider]

That's really the gist of it. They have much, much more experience in this than anyone else. I think we have to recognize that they probably have a pretty good handle on how to manage this. And it certainly is a pleasure to drive it the way Tesla has implemented it. Even my wife, who cannot by any stretch of the immagination, be less technically inclined that your wife or father, likes it.

Thanks for the Tesla party line.
Blended braking is used on many times more vehicles than Tesla has produced or is likely to in the near future.
Technical inclination is unrelated to one pedal driving preference. Would it surprise you if one of the two (between my wife and father) was literally a rocket scientist? Will your preconceptions and biases lead you to an assumption of which one?

Just because AJ likes it one way does not make other preferences less valid or something a manufacturer should not design for. Off road users apparently want adjustable regen from the throttle. That is outside of my scope of experience and apparently from your POV it is a useless feature since Tesla doesn't do it.

 

[SoCal Rob]

I understand but is that a good thing? Can't think of a better example of the leading a horse to water thing. I don't see much difference between pushing a different pedal in to increase breaking effort or letting the same pedal come back to do the same thing except that using the same pedal is definitely easier and more intuitive - forward to go faster - backwards to go slower but that's me.

While I like the concept of one pedal driving, I wouldn’t want to use it until all our vehicles support it.

I’ve seen issues with switching back and forth between vehicles with regular cruise control and adaptive cruise control. While I don’t mind going through the, “Why isn’t the car slowing d… wrong car!” as I’m approaching a slower vehicle, for me braking is simply too critical and time-sensitive (down to fractions of a second) at high speeds to risk making the adjustment between vehicles.

When I constantly switch between vehicles I want them all to behave the same for braking to maintain consistent reaction / muscle memory. I think it is a safety issue.

 

[SANZC02]

While I like the concept of one pedal driving, I wouldn’t want to use it until all our vehicles support it.

I’ve seen issues with switching back and forth between vehicles with regular cruise control and adaptive cruise control. While I don’t mind going through the, “Why isn’t the car slowing d… wrong car!” as I’m approaching a slower vehicle, for me braking is simply too critical and time-sensitive (down to fractions of a second) at high speeds to risk making the adjustment between vehicles.

When I constantly switch between vehicles I want them all to behave the same for braking to maintain consistent reaction / muscle memory. I think it is a safety issue.

Not sure that should be much of a concern.

I have a Jeep Grand Cherokee which has literally no slowing when you left off the accelerator, literally like it is free wheeling like no other car I have ever owned. I go between that and the Tesla all the time and it has never been an issue.

More of an issue when the Tesla battery is full and you do not get the expected slowdown. I rarely have a full battery and that makes it even more of a surprise.

 

[thrill]

While I like the concept of one pedal driving, I wouldn’t want to use it until all our vehicles support it.
I’ve seen issues with switching back and forth between vehicles with regular cruise control and adaptive cruise control. ...

While it's only a single anecdatum point, I switch driving between an i3s with regen and a clutched z4m frequently, and find no issues in the different driving feels. As for the adaptive cruise in the i3, I detest it, since as you mention, there's a serious lack of good feedback that doesn't require excessive attention. On a whim I decided to test it one day, since I was only going about 45, against a vehicle that kept zooming ahead and then rapidly slowing for traffic, and had come to a stop in front of me. I ended up full anti-skid braking to stop less than a car length behind. Eek - the size of the guy's eyeballs in front of me in his rear view mirror were huge when I finally stopped.

 

[ajdelange]

In one of the test drive videos, adjustable regen was mentioned. That almost certainly means blended braking.

Maybe, maybe not. In the Tesla implementation there were three levels, Full on, medium and off. If off that simply meant that no regen was available. If full was selected that meant as much as could be extracted and if medium was selected that meant that less than the maximum possible would be used. I hope I recalling this correctly but in no case was regen invoked by pressing the brake pedal. That operated the hydraulic brakes.

If regen is solely controlled thru the throttle, the last portion of the pedal travel as you decrease the throttle position has to transition from acceleration to braking, then gradually apply more regen braking until the throttle is "off" and you have 100% regen slowing the vehicle.

It helps to appreciate that the skinny pedal isn't a throttle but rather a device which controls the angle of the stator field relative to the rotor PM field. If the pedal is pressed in farther it moves the stator field forward (in the direction of rotation when the vehicle is moving forward) of the rotor field, more torque is produced in the forward direction and the rotor and vehicle speed up. If the pedal is moved backward the stator field gets behind the rotor field and torque is generated in the direction which slows the rotor and the vehicle. (Note: I'm describing what happens in a PM synchronous motor because that's the kind of motors Rivians have. Where IM's are involved torque is controlled by adjusting inverter frequency rather than phase but the concept is basically the same.)

When adjustable regen is used, the last portion of the throttle release is "mapped" to the brake pedal. Applying the brakes adds in additional regen over and above what is available by being 100% off of the throttle.

When adjustable regen in use the gain of the control system is reduced - the same amount of backward pedal movement produces less field angle shift. In systems where the brake pedal controls regen then the brake control must assume some of the skinny pedal's function IOW it must be able to shift field angle in addition to controlling the hydraulic brake system. This, clearly, makes the friction brake system more complicated and may be one of the reasons that Tesla does not, AFAIK, do things this way.

Tesla has no mechanism for that - the throttle pedal controls only the motors, the brake pedal only the friction brakes (sometimes the computer will intervene on either).

True, AFAIK.

When Tesla had adjustable levels, regen potential was lost because it could not be mapped to the brake pedal.

Which made it kind of a dumb thing to do. But why would you want to "map" part of regen control to another pedal when it is completely controllable from the skinny pedal? Because it makes it more like an ICE car? I ask again is that a good thing to do?

I suspect that adjustable regen went away on Teslas as part of the effort to maximize EPA ratings.

One way or the other a BEV wants maximum regen at all times excepting those where friction brake is required for safety as that leads to longer range on a charge. EPA be damned, we all want better consumption numbers. Clearly another motivation is the simpler friction brake system. Why give that up if the one pedal system costs nothing in the critical Wh/mi department?

I get it that some people don't like the new paradigm but is there any other reason not to use the one pedal interface?

 

[ajdelange]

Thanks for the Tesla party line.

Elon Musk did not approve this message. And BTW, I'm not on a Rivian site to pump my Tesla stock. If I could get it I'd have Rivian stock too.

Blended braking is used on many times more vehicles than Tesla has produced or is likely to in the near future.

Interesting. I'd like to see some numbers on that mostly as Tesla continues to dominate the market I'd like data on how much. There used to be monthly reports on sales by maker but they seem to have dissappeared.

Technical inclination is unrelated to one pedal driving preference. Would it surprise you if one of the two (between my wife and father) was literally a rocket scientist? Will your preconceptions and biases lead you to an assumption of which one?

Rockets brake with thrusters but that aside no, it wouldn't surprise me. I have worked with some brilliant men who couldn't figure out how to turn their monitors on.

Just because AJ likes it one way does not make other preferences less valid or something a manufacturer should not design for.

No, of course not. That's why I keep asking if there is some other reason for blended. There is no technical limitation to the one pedal approach and there are technical costs associated with blended.

Off road users apparently want adjustable regen from the throttle.

Why? Is there a valid technical reason?

apparently from your POV it is a useless feature since Tesla doesn't do it.

No, it appears to be a useless feature because I can't see any technical merit in it. So I ask again, are there any technical merits? The fact that Tesla has come to the same conclusion does, however, back up my conclusion to some extent. I'm sure that if Tesla thought failure to provide blended regen were costing them sales they would provide it. As they have moved in the opposite direction I think they have concluded the opposite. Thus I don't see a marketing advantage here either.

 

[DuckTruck]

Hey @DuckTruck , not sure if you've been following this thread. You're the only one I know that's actually had the amazing opportunity to sit at the wheel of an R1T.

What was your experience / impression with how Rivian is handling the breaking system? One Pedal or more Blending Braking? Did you happen to notice / experience different levels of regen braking that the driver can adjust?

Thanks again for all your time in sharing your experience with all of us ??

Scott
PNW R1S Oct'18 res holder

Scott,

In short, this thing has true one-pedal driving capability. With regen in level 4, at around-town speeds, you won't need the brake very much. The regen is really phenomenal and it did bring me to a stop, even though I instinctively put my foot on the pedal every time.

There are four settings. I believe the first pretty much replicates an ICE-mobile in that it feels like it slows gradually, like we're used to, and probably provides a small amount of recharge.

From there, it gets progressively more aggressive in its regen-braking ability. I'm pretty certain we switched between levels 1 & 4 during my test drive with little, if any time in 2 & 3. With it in level 4, you have true one-pedal driving. At slower speeds, the regen kicks in immediately and you begin slowing like now. I've been told the brake lights come on immediately, as would be appropriate for a suddenly-slowing vehicle.

I made a mistatement when I was talking about my high-speed run to 130 miles an hour in my interview with the guys at Rivian Stories. I know I said when I lifted my foot to head for the brake pedal that the heavy regen had already aggressively begun. It was really a more natural type of slowing, rather than being some sudden braking event before I elected. It comes on, but not like you've slammed on the brakes at 130. I'm sure it does that for safety reasons. That said, in level 4, it would bring you to a stop eventually, and it will do so in fairly short order. The nice thing is that the brakes are really stout and have a solid feel throughout the range of usage. Stops were nice and controlled, even when steering while braking.

In my ELR, there is only one level of regen plus a one-pedal mode on the "Gear Selector". If I use my steering wheel paddles, which actuate the regen in that car, the regen is set to .2 g's worth of slowing. On top of that, it won't bring the car to a complete stop, so I have to at least finish the stop with the brake pedal.

In the R1T, it brought me to a complete stop in level 4. My rough guess is that it was about .4 g's worth of stopping power, but that's just a rough estimate. What I can say is that it has much stronger regen than the ELR/Chevy Volt. I don't know if levels 2 and 3 will bring it to a complete stop, but knowing level 4 is as stout as it is, I know I have one-pedal driving when I need it.

It's going to be great to have options so we can dial up exactly what we need in any given situation. For off-roading, I imagine level 4 will be ideal, as it will be for some road applications, as well.

People will need to get used to it though, because if you lift your foot in anticipation of that stop sign that's 200' away, you're gonna come up waaaay short.

I hope this helps, Scott. Feel free to ask any other questions you might have. If you want to talk about this, or anything else, message me with your number and I'll call you.

I can't wait to hear others' takes on this amazing vehicle, once test-drives start, and especially after deliveries occur.

Take care!

 

[SoCal Rob]

Not sure that should be much of a concern.

I have a Jeep Grand Cherokee which has literally no slowing when you left off the accelerator, literally like it is free wheeling like no other car I have ever owned. I go between that and the Tesla all the time and it has never been an issue.

More of an issue when the Tesla battery is full and you do not get the expected slowdown. I rarely have a full battery and that makes it even more of a surprise.

We all have different capabilities, priorities, and concerns. I don’t know how easy it is to overlook which vehicle you’re in while focused on the road ahead. If your Tesla is a sedan with a black interior and your JGC is a tall SUV with a tan interior, I could see that helping to avoid the minute time spent on, “Do I need to use the brake pedal at all? If yes, then how much braking do I need?”versus, “How much braking do I need?”

Ultimately, if I’m wrong and being too cautious there are no serious negative consequences switching back and forth between vehicles. Other than having to move my foot between accelerator and brake, the only other downside I can think of is wasting energy which could have been captured from regen, and I consider that trivial. I‘m making an assumption that even with minimal regen, the Rivian will use AEB when there is sudden accelerator lift combined with obstacle detection. Maybe my assumption is bad or I’m missing something else to make me reconsider?

If I opt to go with 2 different behaviors for braking in 2 vehicles and I’m wrong the negative consequences are potentially bad for me, bad for passengers in my vehicle, and bad for whatever or whoever I hit with my just-under-3-tons-while-empty Land Rover which, unlike the similar weight and configuration future R1S, doesn’t have AEB to mitigate any deficiencies in reaction time.

If keeping my muscle memory and reaction time at their best means that in an emergency I stop 5 feet before hitting a kid because I reacted a fraction of a second faster versus 5 feet AFTER kitting the kid, I’ve made the right decision. If I slow down even a little bit because of vehicle behavior difference, I don’t want to be haunted by, “If I kept my braking interface consistent would I have avoided this?”

I’m probably being too conservative, but when looking at the potential risk to reward, I cannot see me changing my mind until I get to do some real-world testing with different Rivian regen levels. Once all of our vehicles are single-pedal capable, then I’m all-in on single-pedal driving.

 

[Dark-Fx]

Scott,

In short, this thing has true one-pedal driving capability. With regen in level 4, at around-town speeds, you won't need the brake very much. The regen is really phenomenal and it did bring me to a stop, even though I instinctively put my foot on the pedal every time.

There are four settings. I believe the first pretty much replicates an ICE-mobile in that it feels like it slows gradually, like we're used to, and probably provides a small amount of recharge.

From there, it gets progressively more aggressive in its regen-braking ability. I'm pretty certain we switched between levels 1 & 4 during my test drive with little, if any time in 2 & 3. With it in level 4, you have true one-pedal driving. At slower speeds, the regen kicks in immediately and you begin slowing like now. I've been told the brake lights come on immediately, as would be appropriate for a suddenly-slowing vehicle.

I made a mistatement when I was talking about my high-speed run to 130 miles an hour in my interview with the guys at Rivian Stories. I know I said when I lifted my foot to head for the brake pedal that the heavy regen had already aggressively begun. It was really a more natural type of slowing, rather than being some sudden braking event before I elected. It comes on, but not like you've slammed on the brakes at 130. I'm sure it does that for safety reasons. That said, in level 4, it would bring you to a stop eventually, and it will do so in fairly short order. The nice thing is that the brakes are really stout and have a solid feel throughout the range of usage. Stops were nice and controlled, even when steering while braking.

In my ELR, there is only one level of regen plus a one-pedal mode on the "Gear Selector". If I use my steering wheel paddles, which actuate the regen in that car, the regen is set to .2 g's worth of slowing. On top of that, it won't bring the car to a complete stop, so I have to at least finish the stop with the brake pedal.

In the R1T, it brought me to a complete stop in level 4. My rough guess is that it was about .4 g's worth of stopping power, but that's just a rough estimate. What I can say is that it has much stronger regen than the ELR/Chevy Volt. I don't know if levels 2 and 3 will bring it to a complete stop, but knowing level 4 is as stout as it is, I know I have one-pedal driving when I need it.

It's going to be great to have options so we can dial up exactly what we need in any given situation. For off-roading, I imagine level 4 will be ideal, as it will be for some road applications, as well.

People will need to get used to it though, because if you lift your foot in anticipation of that stop sign that's 200' away, you're gonna come up waaaay short.

I hope this helps, Scott. Feel free to ask any other questions you might have. If you want to talk about this, or anything else, message me with your number and I'll call you.

I can't wait to hear others' takes on this amazing vehicle, once test-drives start, and especially after deliveries occur.

Take care!

Did the truck display how many kW was being returned to the battery? In my Bolt EV in L mode, it maxes out at 70kW with also using the paddle. The stopping power is enough to stop at pretty much any stoplight that changed that I was going to stop at anyway. The exception is if I'm going quite a bit over the speed limit or have traffic in front of me stopping suddenly, I might also need to use the brake pedal.

 

[SoCal Rob]

I get it that some people don't like the new paradigm but is there any other reason not to use the one pedal interface?

I like max regen one pedal driving, and I’ll happily switch when all vehicles I own are equipped with it. Regarding my rationale for keeping the braking behavior consistent across vehicles I own, I wrote this.

 

[DuckTruck]

Did the truck display how many kW was being returned to the battery? In my Bolt EV in L mode, it maxes out at 70kW with also using the paddle. The stopping power is enough to stop at pretty much any stoplight that changed that I was going to stop at anyway. The exception is if I'm going quite a bit over the speed limit or have traffic in front of me stopping suddenly, I might also need to use the brake pedal.

With what I was doing off-road, and the speeds involved during my test drive, I was way more focused on what was I was seeing through the windshield than to notice the regen's give-back to the battery. That stout feeling of regeneration in level 4 tells me it is providing a good amount of juice back to the battery, though.

I'm thrilled not only by what it will do in level 4, but that we do have multiple options available.

 

[ajdelange]

First many thanks for posting this (and the other things too)

In short, this thing has true one-pedal driving capability.

Relieved to hear that but didn't doubt it.

With regen in level 4, at around-town speeds, you won't need the brake very much. The regen is really phenomenal and it did bring me to a stop, even though I instinctively put my foot on the pedal every time.

You'll get used to it and come to love it.

There are four settings. I believe the first pretty much replicates an ICE-mobile in that it feels like it slows gradually, like we're used to, and probably provides a small amount of recharge.

From there, it gets progressively more aggressive in its regen-braking ability. I'm pretty certain we switched between levels 1 & 4 during my test drive with little, if any time in 2 & 3. With it in level 4, you have true one-pedal driving. At slower speeds, the regen kicks in immediately and you begin slowing like now.

A little (very little physics). The acceleration, a, experienced by a vehicle of mass m is a = P/(m*v) where P is the power delivered to or taken from the motors and v is the velocity in the forward direction (for this discussion). At slow speed for a given amount of power a is large because v is small. That's why it feels as if it is really grabbing at low speed and feels more like ICE engine decelleration at higher speed. By limiting the amount of P taken (lower levels of regen) you can clearly limit a. And, this won't cost you a joule if you manage it in such way that you don't have to use the friction brakes (see hypermiling comment below). I don't see the necessity to have 4 gain settings as the pedal is a continuous gain control. Perhaps Rivian will learn this as Tesla did and remove it via OTA update as Tesla did. Or perhaps they won't.

I've been told the brake lights come on immediately, as would be appropriate for a suddenly-slowing vehicle.

I believe that is required by law.

I made a mistatement when I was talking about my high-speed run to 130 miles an hour in my interview with the guys at Rivian Stories. I know I said when I lifted my foot to head for the brake pedal that the heavy regen had already aggressively begun. It was really a more natural type of slowing, rather than being some sudden braking event before I elected. It comes on, but not like you've slammed on the brakes at 130. I'm sure it does that for safety reasons.

No, that's because of a = P/(m*v). There is a limit as to how fast Rivian wants to charge the battery. That sets an upper limit on P which in turn limits a. [Note: g = a/9.8]

The nice thing is that the brakes are really stout and have a solid feel throughout the range of usage. Stops were nice and controlled, even when steering while braking.

Is that referring to regen braking or the friction brakes?

I don't know if levels 2 and 3 will bring it to a complete stop, but knowing level 4 is as stout as it is, I know I have one-pedal driving when I need it.

Theoretically yes but there are going to be practical limitations and there will probably be some software choices as in do we want "creep" or "hold" when coming to a stop.

It's going to be great to have options so we can dial up exactly what we need in any given situation. For off-roading, I imagine level 4 will be ideal, as it will be for some road applications, as well.

I think it will too to the point that my guess would be that Rivian will remove the other levels.

People will need to get used to it though, because if you lift your foot in anticipation of that stop sign that's 200' away, you're gonna come up waaaay short.

Remember the fuel crisis of 1973 and how we learned to "hypermile"? Part of that was knowing when to take your foot off the gas pedal so that you came to a stop right at the line at a stop sign or light. Exactly the same skill is involved here.

 

[Dark-Fx]

I like max regen one pedal driving, and I’ll happily switch when all vehicles I own are equipped with it. Regarding my rationale for keeping the braking behavior consistent across vehicles I own, I wrote this.

I regularly drive different vehicles. I have occasionally reached for the non-existent regen paddle when driving my camaro with a stick, but in an emergency situation I've never not moved my foot to the brake pedal. Regen will probably never match how fast you can fully stop by stabbing the brake pedal. As long as you maintain that muscle memory, IMO it doesn't matter what you're driving.

I'm actually more thrown off when I drive my wife's Volt because when the battery is nearly full, it doesn't offer any hints on how much total regen you have available. It's also not nearly as powerful as the regen in my Bolt. I often end up overshooting stops and needing to additionally use the brake pedal way more often. The Volt also seems to be able to come to a complete stop occasionally but then creep mode kicks in and I have to quickly jump to the brake pedal.

I was pretty interested in the Taycan until I found out Porsche decided they didn't want a one-pedal driving mode.

 

[DucRider]

Bottom line is that Rivian offers 4 levels of regen.
Those that want one pedal driving have that option. Those that want a different experience have that choice.
Removing the option just because Tesla did would be as silly as redesigning the R1S to have falcon wing doors and only two motors because that's what Tesla did on the Model X.

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