i3 Right Pedal: is Speed or Power Commanded?

[electrons]

I saw an i3 at the Denver Auto Show a few days ago, and have seen a few around town too. I've never driven one.

My question for experienced owners: Are you commanding Speed with the right pedal? (On most conventional gasoline fueled cars, the acceleration (right) pedal has historically essentially commanded Power.)

Let me put it another way. Do you feel like you can fix your speed going up and down hills by maintaining the same physical position on the right pedal (speed proportional to pedal position)?

Love the i3! I recently bought (and like) a Ford Focus Electric, costing me $16k after all rebates, and I don't believe it has the aggressive regenerative action when lifting off the right pedal, unless you put it in Low instead of D, where it does.

I'm already thinking I'd rather have the BMW i3, which of course would have cost more, estimated $26k after all gov rebates (fed+state), compared to the $16k for the Focus Electric I have now.
Carbon composite body structure is beyond cool, I know.

I'm not sure I like the idea of having the i3 get that aggressive with regen after lifting off the 'gas pedal' though. I'm an engineer with a background in Control Systems (aircraft mostly), and for a human foot to control power via pedal position is what we are used to.

 

[alohart]

I'm pretty certain that it's still a power, not speed pedal. If one is driving at a steady speed on a level road, an incline will decrease speed unless the pedal is pressed down to increase power. I drive almost 100% with adaptive cruise control on, so the power changes necessary to maintain the set speed are automatic including reduced or even negative power or friction braking, if necessary, to avoid colliding with a slower vehicle in front.

Our former Mitsubishi i-MiEV had 'B' drive mode which I think stood for "braking". Even 'B' mode didn't provide as much regenerative braking as our i3, and because our i-MiEV had a creep feature, regenerative braking would never stop it totally. I always drove in 'B' mode because I like one-foot speed control.

The i3's November software update delayed the strong regenerative braking that occurred when suddenly lifting off the accelerator pedal or turning off cruise control. "Negative power" is now much more controllable making one-pedal driving even easier and less abrupt. I think that most i3 drivers really like the strong regen and have quickly learned how to use it to almost totally avoid pressing the brake pedal.

Many EV's offer various regen strengths either via different driving modes or a steering column paddle, but I wonder why one would want settable regen strengths when the position of the i3's accelerator pedal determines a continuous range of regen strengths with no need for different driving modes or paddles.

 

[louisgrenier]

I'm not sure I like the idea of having the i3 get that aggressive with regen after lifting off the 'gas pedal' though. I'm an engineer with a background in Control Systems (aircraft mostly), and for a human foot to control power via pedal position is what we are used to.

Depending of your input control, it isn't "that" agressive. You do control the level of deceleration. If you want to compare to some aircraft, it is a bit like the one lever control of the Cirrus aircraft. Controlling both the power and the prop. It is like if you have a lot of drag that you circumvent by the position of the pedal. Push it, you have acceleration. Remove pressure, you have constant speed. Remove more pressure, you have deceleration. The level of deceleration is a factor of the pedal position. You don't have to lift off the gaz pedal to have deceleration from the regen. Regen will starts at a certain position with your foot on the lever controlling the amount of it. It isn't an ON-OFF thing. Deceleration and regen does not start when you have your foot off the pedal. It starts gradually. You control the level of deceleration that you want (need) with your foot. Nothing different than from fancy sports car like a Porsche with use a lot of engine deceleration when you listen the pressure on the pedal. Except that it will do it even at low speed. The sports car will stop deceleration since it have to keep a minimum RPM to the engine. In the i3, you will control the same deceleration to the complete stop since the engine does not have to keep a minimum RPM.

In fact, your foot is almost all the time on the pedal. It is, like the Cirrus, almost a one lever controlled acceleration-deceleration thing. Wich you get customized to in minutes. Compare to a two lever ( three if you have a clutch) acceleration-deceleration control, it is more natural in a magnitude. One lever, that will control level of acceleration-deceleration all the way. Going back to the Q5 is now very weird and show how bad a gaz pedal is as an interface to control speed.

Louis

 

[electrons]

Great discussion, Art & Louis. This whole "pedal speed control" discussion reminds me of the end-goal of controlling the velocity vector on an aircraft (speed and direction).

The different control method in the i3 was noted in some youtube test drives & articles, and I'd agree it sounds like its easy to get accustomed to quickly.

Even my Ford Focus Electric feels differently enough from my BMW 530xi (especially in 'Low' instead of 'D'), a conventional gas pedal control, for me to notice a difference.

Now I want to run over to the BMW dealer and test drive the i3 up and down some hills, as it sounds like it mixes some coasting behavior with speed-proportional control. Of course if I do that, I'll trade in my BMW 530xi on the spot.... Tempting. ..... Carbon composites & RWD electrics r calling my name.

Human Factors, whatever makes it easier to drive, right?

 

[alohart]

Now I want to run over to the BMW dealer and test drive the i3 up and down some hills, as it sounds like it mixes some coasting behavior with speed-proportional control.

True coasting occurs when the i3's power meter is centered (i.e., zero power) between the positive power side (right) and negative power (i.e., regen) side (left). It feels like the accelerator pedal position for coasting isn't just one exact position between acceleration and regen but maybe a small range of positions that make coasting a bit easier to attain. It can be almost a game to try to never press the brake pedal and to coast as much as possible.

 

[jadnashuanh]

If you anticipate the current situation, light changes, someone slowing to turn, etc., of the vehicles around you, unless someone does something dumb, you almost never need to use the brake pedal. If you ARE using the brake pedal, you're not being as efficient as you could be. You do NOT need to be slow, or abrupt to get decent efficiency from the i3, and if your driving seems jerky to you or your passengers, you have not mastered the concept of the i3's one-pedal driving style. It isn't hard, it's just different. As said, the closest analogy is probably a high compression engine with a manual transmission except you do get to keep that reaction all the way to zero since the motor gladly will stop, unlike an ICE, at least smoothly!?

 

[electrons]

For comparison, Ford/Magna did something similar with my Focus Electric Magna-sourced powertrain. The Focus does do some regen when coasting, but not too aggressively if you stay off the brakes, mostly just conserving your 1/2mv2 kinetic energy. Brakes blend regen (at first with light braking) with disc rotor action when braking harder.

Only problem I have with too much regen after accel pedal liftoff, is that charging batteries is not 100% efficient, I think something like 80% on average depending on amps flowing in. Conserving all or almost all your kinetic energy through coasting seems to give better range numbers. I think BMW considers a person will adapt and adjust pedal inputs to give smooth speed response anyway, so it may not be an issue. In other words, we really drive whatever speed required for the road/traffic situation.

I think the BMW i3 is unique in that 0.13g of deceleration (from regen or brake pads regardless) activates the brake lights, not so on the Focus Electric or Leaf or Tesla to my knowledge.

 

[louisgrenier]

Yu are probably familiar with the reverse engineering of the i3 that you can find on youtube. Pretty well done to communicate their own astonishment. But not so much details about the programming.

 

[jadnashuanh]

I think that the bottom line is: the i3 allows you to control the car from cruising, accelerating, coasting, to adjustable levels of regen (braking) all by adjusting your right foot without having to deal with adjusting anything else, levers, modes, etc. The regen CAN be fairly aggressive, but it WAS decreased from maximum because new drivers complained (I, and many others that had their cars for awhile and understood what was going on, regretted the decrease in regen) during one of the software updates. IT was further refined to come on a bit more gradual when your cruise control was deactivated. FWIW, it did not take me more than a day or so to become fairly proficient in the use of the pedal and achieve smooth driving. I can generally coast without looking at the display to check the position of the power use gauge.

 

[alohart]

The regen CAN be fairly aggressive, but it WAS decreased from maximum because new drivers complained (I, and many others that had their cars for awhile and understood what was going on, regretted the decrease in regen) during one of the software updates. IT was further refined to come on a bit more gradual when your cruise control was deactivated.

Do you think that regen was actually decreased or that only the onset of regen was delayed and maybe ramped up when the accelerator pedal is released or cruise control turned off? To me, it feels like the regen level hasn't decreased but only the onset of regen has been delayed and ramped up. But it's difficult for me to say for certain. Our i3's software was updated from July, 2014, to November, 2015, in a single step, so we missed any regen changes that might have occurred in intermediate software versions.

 

[jadnashuanh]

On the fall 2014 s/w update, it was reported that the index factor for regen was changed from a value of 27 to 24, so yes, if you owned an i3 that early, it did change, and yes, I did notice. The last s/w update did change the abruptness of the regen, but the original max value used to be higher.

 

[TheNickGuy]

Any way to increase the value via a coding change?

 

[jadnashuanh]

Sorry, I have no idea...

 

[electrons]

The regen CAN be fairly aggressive, but it WAS decreased from maximum because new drivers complained (I, and many others that had their cars for awhile and understood what was going on, regretted the decrease in regen) during one of the software updates. IT was further refined to come on a bit more gradual when your cruise control was deactivated.

Maybe people were complaining of calf muscle fatigue from constant force on the pedal. In most cars, going down hills etc. gives the foot a quick rest.

Ford's Focus Electric likely mimics the BMW i3's control method when 'Low' is selected. I tried that some more yesterday and you hardly have to use the brakes at all; maybe similar to the i3 there. Selectable 'D' or 'Low' in the Focus E. (Here 'Low' means more regen, since it only has the typical 1-speed reduction gear like most e-cars.)

I'm assuming the i3 doesn't have a 'Low' (mo' regen than D) available? That would satisfy everyone.

Any way to increase the value via a coding change?

That would be cool if we could alter the vehicle software. Tuners of other vehicles have been able to change numbers in parameter tables at least. I've worked in aircraft control software/systems in the past, and would luv to alter or add algorithms in addition to parameter changes in my cars! Dangerous maybe, yes.... The EPA would go nuts if you tried that in gas-powered cars of course, and manufacturers would be concerned about people injuring themselves and proprietary intellectual property getting out.

 

[jadnashuanh]

The force required to press the pedal on the i3 is less than most other cars I have owned...IOW, the few times I can actually coast is not an issue at all. And, given that feathering the pedal is easier than moving to the brake pedal and braking, I think people have trouble with change and learning a new skill! Given the nominal range of the vehicle, and if you're going to be driving longer distances you'd probably be using the cruise control, it is a non-issue for me and I thought those people that complained about the strong regen just didn't get a good intro to the car or were Luddites. The i3 is not the same as a 'normal' car, and was not intended to be. It takes some (small) skill to actually operate it at peak efficiency and comfort. It's about the same with a high performance, high compression manual transmission vehicle...in one of the lower gears, letting off on the gas will give you significant braking effect - in some cases, probably more than the i3 ever had. One either learns that fairly quickly, or is doomed to jerking the car and passengers around. Much todo about nothing, IMHO.

 

[electrons]

OK, I see now. I test drove an i3 today! Yep, like I thought, its very similar to driving a Ford Focus Electric around in 'Low' on the transmission selector.
Certainly do think BMW should make a settable option how much slow-down regen occurs, say set a number from 1 to 3 for how much you prefer when you drive.

The i3 certainly doesn't suffer from the torque-steer the Focus Electric has. Also, being front wheel drive, the Focus Electric limits wheel spin a lot when launching (slow to launch, amps-limiting too), something the i3 just digs in and does quicker with its RWD. The i3 is the quickest BMW 0-30 mph, nice.

People complained because pedal-feel was a little different. I think its better to use pedal lift-off to slow down, as BMW does, keeping your right foot in place more instead of having to switch to braking as often. BMW got it right. The end goal is to control speed where you want it, and thats e-z in the i3.

I felt like it was the year 2025 when driving it today. This is where things are headed.

 

[electrons]

After driving a BMW i3 and being impressed....... Should I buy a $40k BMW i3 today?
Or wait a year or two for a cheap lease-returned used BMW i3? (Should be cheap given all the 200-mile range cars coming out in a year.)
Or put $1k down today on a Tesla Model 3 to get in 2 to 2.5 years from now?
Decisions. Meanwhile, the fun Focus Electric I have now will suit me. Still jealous of the i3 owners though.

 

[louisgrenier]

make a settable option how much slow-down regen occurs, say set a number from 1 to 3 for how much you prefer when you drive..

There is already two way to control level of regen. The three different Eco mode, the small button near the left knee, adjust the sensivity of regen the gaz pedal will do. And then, you have the gaz pedal that give you infinite adjustment of regen depending on it's position.

Louis