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Is lack of no automatic hold for a 2017 Model S, software or hardware limit?

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2101Guy

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Jan 6, 2020
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So nice in my wifes Model Y to not have to touch the brake pedal to engage the "H" feature.

I assume there is some sort of hardware limitation that prevents a 2017 Model S from having this function? (I still have to depress the brake pedal to engage the H, of course)
 
So nice in my wifes Model Y to not have to touch the brake pedal to engage the "H" feature.

I assume there is some sort of hardware limitation that prevents a 2017 Model S from having this function? (I still have to depress the brake pedal to engage the H, of course)

It's related to the motor technology, since some types cannot provide regen braking below a certain rotation rate. So it's hardware not software. I guess it would be technically possible to use the regular brakes for the last bit of braking, but doing so smoothly would be a challenge.
 
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Lack of automatic hold down to zero *by regen* is a hardware limit. Permanent magnet motors in the Raven/3/Y are able to take the regen energy all the way down to 0 RPM because the magnetic field is *permanent*. Induction motors need a threshold current flowing through them to remain operational, thus there is a dropoff point where operational energy>regenerated energy.

That said, there is no reason that it could not be compensated for in software. Autopilot clearly has the ability to take vehicle speed down to zero with regen + brakes, so it's just Tesla being lazy and telling you to buy a new car if you want true one-pedal driving.
 
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I would argue software limitation. While the PMS motor of the Y/3 is used to get down to 0 mph for the auto hold feature, there is no reason the model S can't gently actuate the brake to achieve the same thing. I disagree with the above poster, I think a computer could do it smoother than a human no problem. TACC already uses the brake to stop at 0 mph in stop and go traffic no problem.
 
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I disagree with the above poster

What are you disagreeing with? We said the exact same thing.

I can already do this in my S when I've regen to as slow as it'll go

that’s just it - you are applying power, therefore keeping the AC induction motor energized. Automatically hold is currently implemented by using the permanent magnet motor’s property of permanent magnetic field and induced current to take energy from the vehicle system all the way down to zero.
 
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That said, there is no reason that it could not be compensated for in software. Autopilot clearly has the ability to take vehicle speed down to zero with regen + brakes, so it's just Tesla being lazy and telling you to buy a new car if you want true one-pedal driving.

But then people would complain that the brake pedal makes more noise clicking and clunking and not be happy. Like with the new features bogging down the MCU1 - sounds good on paper but then the real problems show up in the field. I feel like it's better that they just draw the line somewhere.
 
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What are you disagreeing with? We said the exact same thing.



that’s just it - you are applying power, therefore keeping the AC induction motor energized. Automatically hold is currently implemented by using the permanent magnet motor’s property of permanent magnetic field and induced current to take energy from the vehicle system all the way down to zero.

But they could still implement automatic hold in software which was my point.
 
TACC already uses the brake to stop at 0 mph in stop and go traffic no problem.
Yes, you are right about the TACC but it uses sensors to keep limited (set by user) distance from obstacle ahead. You need to determine a threshold for “HOLD” in the absence of any object in Autosteer environment and this is not there, hence without TACC you need to apply brakes to be standstill.
 
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I guess I should clarify they could do it in software without having to use the brakes. What I'd really like to see is hold when coming to a stop on an up hill. I usually come to a complete stop at stops going up a hill without pressing the brake pedal and then I just modulate the throttle to keep from rolling backwards. I could engage hold with the brake pedal but then I'd have to remove my foot from the throttle. Yes, they could detect this scenario and engage the brake pedal but this is sometimes clunky and not very smooth. It would be far better if they chould just software modulate the DUs, like I do manually, to keep from rolling backwards.
 
I would argue software limitation. While the PMS motor of the Y/3 is used to get down to 0 mph for the auto hold feature, there is no reason the model S can't gently actuate the brake to achieve the same thing. I disagree with the above poster, I think a computer could do it smoother than a human no problem. TACC already uses the brake to stop at 0 mph in stop and go traffic no problem.

Actually you're correct of course, my bad for answering a question late at night. Which brings up the more interesting questions of how well the car blends regen vs braking when on Autopilot (something I'd looked at before but never reached a conclusion).
 
I always thought that the models that have true one pedal driving (Aka cars with the PM motors) have the ability to regen almost all the way to 0kmh but the last bit still use the friction brakes. Regardless I don’t see why Tesla cant add that feature to non-PM motor cars