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Regen braking to stop? (similar to BMW i3)

Discussion in 'Model X: Driving Dynamics' started by Curbine, Jun 20, 2016.

  1. Curbine

    Curbine Member

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    Hello, apologies if this has been discussed but the keywords seem to be quite common.

    I bought an i3 while waiting for the Model X. Really love it actually--if the size/range meets your needs, it's an amazing funny little car. Driving dynamics and everything is superb.

    Had a chance to spend some time with the Model X recently. Wow, what a vehicle. Just amazing. However, I've been spoiled by some things on the i3 that I wish were on the X. I'm curious if anyone feels the same way or knows about future plans.

    Biggest wishlist feature would be true "one pedal driving" like the i3. The regenerative braking is strong and will completely slow the car down to a stop. Very easy to modulate. Takes a day or two to get used to it, but then it's a revelation--you only need to use the brake for unexpected deceleration. It also is very good about keeping the brake applied until you are ready to go again. Just a really polished experience overall.

    Having to use the brake pedal on the X left me feeling like I took a step back in technology. The X/S absolutely could do this with some simple software changes, and I can see why it doesn't--it feels more like a normal car to have the X behavior. The BMW i3 is strange from the moment you see it through learning how it drives, but once you get used to it you wonder how to go back again.

    Anyone else share this feeling? I work in software, makes me wish it was easy to just write custom firmware for the car and share it to whoever wants a similar feeling. Yes there's security/safety issues, but it could be made simple so you can only mess with the bits that are cleared tweakable.

    I also thought the drive selector stalk was kind of an odd "old style" thing that stood out, but that's just minor. Overall I loved the X. Is one Model X worth two or three i3s? That is the real question. But it's amazing no doubt.
     
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  2. deonb

    deonb Active Member

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    Oh, yes. Count me in for that. Totally agree.

    Regen actually used to be a bit stronger, and then Tesla changed it a few years ago. But it was never that strong.
     
  3. aesculus

    aesculus Still Trying to Figure this All Out

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    I would go for the regen to come to a complete stop too. Not sure why it doesn't but perhaps someone with more experience will tell us why.

    For now I just apply the brake when the car gets down to 1 mph or so.
     
  4. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Regen braking to stop uses more energy because the system has to provide power to simulate regen when there isn't enough kinetic energy left to do actual regen.
     
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  5. MP3Mike

    MP3Mike Active Member

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    Are you sure of that? My understanding is that the i3 uses PM DC motors that can regen down to 0, while Tesla uses AC induction motors and they can't regen below ~5 MPH.
     
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  6. chillaban

    chillaban Member

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    The i3 uses PM AC motors, and it is true that AC induction motors are less suited to position control / servo use cases such as regenning to a complete stop.... however, I think the main point here is, even if it wastes energy, why doesn't Tesla simulate regenning to a stop using a combination of motoring and applying the brakes smoothly and automatically?

    As a new Tesla driver, it does seem like it's a bit difficult to smoothly transition between regen slowdown and a full stop without accidentally having the brakes bite a bit too hard. A week later I'm getting pretty good at it, but still, the Tesla automates and improves so many aspects of driving that are in the inconvenient-but-not-insurmountable category... I think this would be another case where it'd be great to have an option analogous to the Creep option for "regen to a stop".
     
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  7. Skotty

    Skotty 2014 Model S P85

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    If not blending regen mostly in the brake pedal, I would prefer they keep it more pure with regen only on the gas. If the motor can't regen to a stop, I'm not a fan of the idea of simulating regen to a stop. It is pretty good the way it is. You only really have to step on the brake when it is time to actually fully stop.

    If you could regen to a stop entirely, people wouldn't press the brake at all, and I have to think there would be issues with that and there is merit to sort of requiring people to actually step on the brake in order to fully stop when not in park.
     
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  8. Electric700

    Electric700 Member

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    This! -> Creep option for "regen to a stop".
     
  9. ThosEM

    ThosEM Space Weatherman

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    Oh gosh! Some want regen on the brake pedal, and others want brakes on the accelerator! I think I'm in the camp of keeping them segregated so one always knows whether energy is being recovered or wasted.
     
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  10. vandacca

    vandacca Active Member

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    We have to keep the brake/accelerator functions separate and simple so that the remaining 99% of the population doesn't confuse them and accidently drive through an elevator shaft.
     
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  11. NikeWings

    NikeWings Member

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    Despite challenging myself to perfect the regen to a virtually complete stop, I find myself lighting tapping the brake the final few feet anyway to keep the cars behind me alert. My eyes are constantly darting to the rear view mirror. If full stop regen triggered intermittent brake lights at say 10 mph in a regen deceleration, then I'd be a fan.
     
  12. woof

    woof Model S #P683 Blue 85 kWh

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    Pretty sure the i3 regen to a stop sometimes applies friction brakes in some situations, such as when the battery is fully charged. When pulling out of my garage after 100% charge, with lots of rust on the rotors due to wet conditions the day before, the grinding sound of friction brakes is quite obvious even though the brake pedal isn't being used.

    The Model S in that situation (full battery, or cold one) will limit regen instead of simulating it. I've never noticed the i3 doing that.

    As for preferring it one way or the other...I drive both an i3 and a Model S daily. I prefer the i3's consistent stronger regen to a stop approach with only accelerator input. I wouldn't mind if Tesla gave us that option, even if it ended up using friction brakes to achieve it.
     
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  13. aesculus

    aesculus Still Trying to Figure this All Out

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    Totally. My braking skills suck now. :)
     
  14. FarmerDave

    FarmerDave Member

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    Wouldn't total non-use of the braking system cause (over time) issues with the hardware? I'm thinking of rusted disks, sticky calipers, etc.
     
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  15. Curbine

    Curbine Member

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    Oh absolutely, I think some people misunderstood. The enduser feel is that, but at some point it must use the brakes. Plus it keeps them held until you press the accelerator again, so you don't roll back/forward. After a slight adjustment period, you realize that it's actually much safer this way. Brake is for emergencies--you lift off the accelerator (which means you instantly are slowing down) and then apply the brake, so there's zero confusion.

    I know it must sound dumb, but once you get used to the "one pedal driving" it feels like the same difference from a manual car to an automatic--you're dropping a mandatory pedal. If I didn't have an i3 I wouldn't know I was missing it. (you must get the same feeling)

    Anyone who has the chance should spend a bit of time with an i3. It's no Tesla, but it is an amazing car in it's own way. A touch bigger, a touch prettier, and more range and it would be a serious competitor. Right now it doesn't feel like they compete because of how different they are.

    Here's to hoping it arrives as an option similar to Creep one day. Seems like an extension of the many options that are already provided.

    Also worth noting is the i3 will always apply the brake lights if the speed is decreasing at some fixed rate, so you never have to "worry" that you're not letting people behind you know you are slowing down. I didn't check--do Teslas do that?
     
  16. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Yes, an accelerometer is used.
     
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  17. timf

    timf Member

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    Owning both the i3 and Model X, I can say without a doubt the Tesla has the better braking system. The i3 has a major issue with its regenerative braking. If you go over bumps or pot holes while the regenerative braking is active, it has a tendency to cut out and then need to ramp up again to full effect. This is a very unnerving feeling when you are expecting to come to a stop but all of a sudden the car begins to coast.

    It is convenient that the i3's regenerative braking can bring the car all the way to a stop, but if you want the brake lights to stay on while you are stopped you have to quickly press and then hold the actual brake pedal. This can lead to some jerky transitions because the general reaction when applying the brakes at a full stop is to press down firmly, and if you do so before the car is fully stopped the reaction is abrupt. The nice thing about Model X is that even though you need to press the brake pedal to come to a complete stop, Auto Hold will then engage so you don't have to keep your foot on the pedal in order for the brake lights to remain lit. It also leads to a smooth transition between regenerative braking and friction brakes since you have to engage them sooner.
     
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  18. Curbine

    Curbine Member

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    I thought the brake lights stay on. You confirmed they don't? I seem to recall checking they did, but that was early on, it's possible that was changed with a later software update. Still, that doesn't seem like a valid reason from a design standpoint--the computer should be able to smooth all of that out and it be invisible to the user.

    I haven't noticed any issue with speedbumps. Maybe I just got used to it early on? Ours is also a BEV, not a REX, not sure if that matters. (the BEV is so much better in my opinion--lighter, so more range and faster, and cheaper) You do have to learn that sweet spot with the accelerator where it's in "neutral"--same as putting in the clutch when going over things like that in a manual.

    I had the Model X overnight, and I noticed at least once that when I took my foot off the brake it started rolling back slightly. Maybe because it's so heavy?

    It's such a great time to have access to all these cars. My other car is a manual 911, so much the opposite end of the spectrum it's crazy. For that car I want nothing to be automated for me, while with an electric car I am all for handing over control to the computer to "interpret what the silly human wants and make it happen safely and smoothly". :)
     
  19. Curbine

    Curbine Member

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    With the i3, and perhaps some other electric cars, you don't need to press the bake at all (except for unanticipated events) and it hasn't caused any problems that I have heard of. For one thing it makes it almost impossible to confuse the pedals because you're not switching between them.

    What merit would there be to require people to step on the brake? Assuming the brake lights are illuminated and the brakes are "held" by the car until the human touches the accelerator, what benefit is there to "requiring" people to press it? I trust the computer to press it more than I trust people to do it.
     
  20. eye.surgeon

    eye.surgeon Member

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    I would love a regen-to-stop capability. Make it an option in the settings at least.
     

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