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Last 2 updates changed The Behavior of TACC

Discussion in 'Model S: Driving Dynamics' started by Scotty, Aug 6, 2015.

  1. Scotty

    Scotty Member

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    The Costa Mesa SC replaced a door handle a few weeks ago,and 'updated' my S85's S/W. I then noticed, with the distance separation setting set to 2, that my MS reacts to me approaching vehicles, particularly big rigs, by braking much farther in advance. I would say it's probably reacting while I'm more than 10 car lengths back, even set to 2, and subsequently when I set it to 1. I just installed the latest S/W a couple of days ago, but it's still 'behaving badly'. I'm concerned, because I do quite a bit of driving, know how my car responds, know how to anticipate and safely merge into the passing lane, but now, all of a sudden, it quickly and very prematurely starts applying the brakes. I would have to say that a following driver would question why I'm applying brakes when I'm still far back, particularly when the left adjacent lane is clear, and I was planning on changing lanes, when POW, it starts braking! Unsatisfactory, because I could and would safely merge without hitting the brakes.

    I'm thinking that Tesla did this change to accommodate the upcoming implementation of autopilot, but I think it sucks. I enjoy driving the car, but not the car driving me.

    Here's my suggestion.

    Keep the '1' through '7' options for distance separation and let my selection control the Tesla's separation, as before. Also add the option 'A' for the autopilot function, where the Tesla does what it's now doing. You can even have the Separation Selector automatically select the 'A' mode when autopilot becomes active, but show a message that it's changing the setting 'for autopilot use'.

    Scotty
     
  2. yobigd20

    yobigd20 Well-Known Member

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    If anything it should allow you closer to a big rig vs normal car bc a big rig can't stop very fast lol
     
  3. randompersonx

    randompersonx Member

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    My question to anyone who is advocating following big rigs closely ... Do you like the look of rock chips in your paint, and enjoy replacing your windshield frequently?
     
  4. NigelM

    NigelM Recovering Member

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    Perhaps the car is being smarter than you think. Drafting can be dangerous and potentially, even if it's just through the reduced drag, the stopping distance be longer than you think. Take a look at average stopping distances and reaction times and even if the car can react faster than you it still doesn't make sense to set yourself too close.

    (My bold) Nothing personal intended but to me that sounds like an oxymoron in the context of your post. ;-)
     
  5. kaneda

    kaneda Member

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    I guess this is human reaction time, what about the TACC / emergency braking reaction time ?
     
  6. Scotty

    Scotty Member

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    I think you have misinterpreted my posting.

    I am not drafting big rigs. In California, big rigs are limited to 55 mph (legally, but they generally run at 59 - 60 mph, in the right lane except when passing). The Interstates are posted at 70 mph for non big-rigs. Here's the scenario. You are driving in the right lane at 70 mph. You are approaching a big rig, say 30 car lengths ahead. You check far enough in advance to verify it's clear. Your separation is set to '3'. As you come up, say 10 to 15 car lengths from the big rig, just as you're getting ready to pull into the left lane to pass, suddenly your car brakes, fairly hard. You pull into the left lane, and then your MS accelerates back up to 70. It doesn't seem to matter what the separator was set to, and after driving 35,000 miles in my MS in 10 months, this has changed in the last 2 updates.

    Scotty
     
  7. Saghost

    Saghost Active Member

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    Well...

    If Tesla is using the Bosch ESR unit I suspect they are, or something comparable, then it is measuring the speed of everything within the radar's field of view (out to 600 feet in the narrower front arc) 20 times per second (every 50 ms). Not sure how long the program loop is - possibly as much as another 50 milliseconds? Bosch boasts that the new iBooster is three times faster than a typical car autonomous braking system, able to achieve full brake line pressure in 120 ms.

    So in the worst case for timing, depending on how fast the computer thinks you're looking at 170-220 ms (.17-.22 seconds) from the time the object in front of you slows until the car is in a panic stop using the radar.

    If the car is using the camera it gets inputs more often, but has to work a lot harder at deducing the velocity of objects likely needing multiple (16.6 ms) frames to be confident enough to brake.

    Of course, most cars can't transition into full braking as quickly as the Model S, so with aggressive programming and normal traffic it won't be much of an issue - the car can pick up on it and start braking before the other car has much delta V built up, and stay ahead of it. However, if someone in front of you hits something, you run out of road really, really fast...
    Walter
     
  8. Scotty

    Scotty Member

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    NigelM,

    I have quite a few miles in my MS, and am pretty acquainted with it's operation. No oxymoron intended.

    When I set the cruise control, the car maintains that speed. That's what I'm expecting the car to do. Now, the TACC feature changes the operation depending on when it's tracking a vehicle ahead of me, in my lane. As I am approaching that vehicle, (at 70 mph, perhaps 20 car lengths back, TACC now overides the cruise control and starts braking, even when the separation is set to 2 or 3. I am driving the car on cruise control, but the car is overriding the setting of separation. Clearly not the way it worked before.

    As far as autopilot is concerned, I would expect autopilot will err on the conservative side of safety and caution.

    Maybe my MS has a problem since the last 2 updates.

    Scotty
     
  9. Khatsalano

    Khatsalano Member

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    I have observed that the settings of 1-7 are actually not car lengths. They are following-distance equivalents in 0.5 second intervals. So, at 7, you have 3.5 second of following distance, regardless of speed.

    Have you tested this too? Let me know if I'm imagining things.
     
  10. ecarfan

    ecarfan Well-Known Member

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    Are you are saying that a TACC setting of 1 means that the following distance is maintained such that if the car you are following was to instantaneously stop (which of course is not possible) you would reach its position in 0.5 seconds if you maintained your current speed?
     
  11. Soolim

    Soolim Member

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    My interpretation is that with setting of 1, your car will be in the position earlier occupied by the car in front of you in 0.5 second.
     
  12. AmpedRealtor

    AmpedRealtor Active Member

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    I would think the numbers are equivalent to seconds. A 0.5 second following distance is totally unsafe. One second makes much more sense to me.
     
  13. Ingineer

    Ingineer Electrical Engineer

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    From the owners manual:

    tacc-distance.png
     
  14. RDoc

    RDoc S85D

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    The newest firmware release seems to have made the TACC much smoother in highway traffic situations like cars changing lanes, sudden slowdowns etc. Previously I felt it was somewhere between very abrupt and dangerous, but the current version seems quite reasonable. My explanation is that they are applying lessons from their work on autopiloting to the TACC.
     
  15. jbcarioca

    jbcarioca Active Member

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    What version are you using now? I recall a couple of updates back,I do not recall the version, there was a quite significant improvement in smoothness at shorter settings (2&3) that made a big advance in stop-and-go traffic. It's logical there would be pretty much continuous improvement from now until we really get the more advanced autopilot features.
    BTW, I may be one of the few who does not mind waiting for the autopilot. I have driven the releases from BMW and GM. Bosch clearly has the responses working well, but real world use is all about the algorithms and the others are not really ready for non-beta release IMHO.
     
  16. ex-Infiniti

    ex-Infiniti New Member

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    I've noticed a similar issue described by the OP. Following the last couple of S/W updates, I noticed a change in the TACC behavior as it relates to the Overtake Acceleration feature. I've done some long trips before and after the upgrades and the behavior is definitely different.

    With TACC active and detecting a vehicle ahead, the car slows appropriately for the distance settings. However, when I indicate a pass by momentarily holding the turn signal and moving into the pass lane, my S85 brakes and slows by as much as 5 mph (e.g. from 65 -> 60) even though the passing lane is clear. I can't determine what is triggering this sudden braking as it doesn't seem to be related to following distance (1-7) or speed of the car I'm following. As the OP points out, this braking while passing can be problematic if another vehicle is approaching in the passing lane as you pull out.

    Looks like there are still some kinks in the TACC behavior that need to be worked out.
     
  17. wcalvin

    wcalvin Member

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    My TACC behavior has changed with recent updates. It maintains speed for too long when approaching stopped traffic, then brakes when only several car lengths to go. Much better behavior back in June-July.
     

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