TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC
  1. TMC is currently READ ONLY.
    Click here for more info.

Tesla Semi Aims to Put an End to Dangerous Jackknifing

Discussion in 'Semi' started by TMC Staff, Nov 17, 2017.

  1. jr4488

    jr4488 Member

    Joined:
    Nov 19, 2017
    Messages:
    19
    Location:
    Los Angles
    You are absolutely right. When the trailer gets sideways, your best chance is to accelerate and pull the trailer straight. An experienced driver allows leaves enough room and keeps the speed low enough to pull the trailer straight in an emergency...
     
  2. Farmertom

    Farmertom Member

    Joined:
    Nov 18, 2017
    Messages:
    86
    Location:
    Alberta
    I think the jackknifing issue might be the unintended benefit of a freaking heavy truck...

    Trucks are designed to put as mush weight as possible on the steering axle (hence the engine, fuel tanks etc. moved as far forward as possible and set back front axles). This makes the rear of the tractor relatively light in an unladen condition and very susceptible to jackknifing.

    Tesla mounting the batteries midship tells me they are achieving maximum weight on the steering axle with virtually nothing in there and must transfer the rest to drive axles thus making this truck much better balanced and controllable.
     
  3. EvanLin

    EvanLin Member

    Joined:
    Oct 9, 2016
    Messages:
    110
    Location:
    Asia
    It's not about how it happens. It's about why it happens.

    If the tractor can keep the truck absolutely straight (via one-side motor and its instant response), how would the trailer "pass" it?
    It's only a problem that "can't slow down enough and hit front obstacles".
     
  4. mongo

    mongo Well-Known Member

    Joined:
    May 3, 2017
    Messages:
    12,857
    Location:
    Michigan
    Sure, which is how SpaceX lands rockets.
    I don't understand your why vs how statement. Situations cause the trailer cg to not be in line with tractor and kingpin. There are the when to your why which create a how.
    Most scenarios involve also needing to decelerate, if there is no need to slow, the tractor can drift the trailer.
    Once there is the need to slow and stay in lane, other effects can remove stability.
    If the semi is on a curve, inertial vector does not line up with centerline.
    Or if the 300 sqft sail gets pushed sidways.
    Or if there is an evasive maneuver (really looking forward to radar and traffic feedback to prevent pileups in whiteouts)

    If the world shifts the trailer and the tires don't hold when the tractor needs to slow in a straight line/ one traffic lane, there is no recovery mechanism since the force vector of the trailer's CG does not line up with the point at which the tractor imparts force to the trailer (creating a rotational vector with no counter). And the tractor can't get them to line up again.
     
  5. EvanLin

    EvanLin Member

    Joined:
    Oct 9, 2016
    Messages:
    110
    Location:
    Asia
    I am just saying op listed a bunch of situations, but not discussing how to solve it.

    Maybe I shouldn't use the word "straight". I should use "zero-torque."
    Even on a curve, if motor-control can achieve a zero-torque environment, there is no jackknifing.

    You can balance a broom upside down while standing still -> like preventing jackknifing on a straight
    You can also balance a broom upside down while moving forward -> like preventing jackknifing on a curve
     
  6. mongo

    mongo Well-Known Member

    Joined:
    May 3, 2017
    Messages:
    12,857
    Location:
    Michigan
    I had originally written in that analogy (with a pencil, not broom). Either the trailer need to grip, or the tractor need to get in line with the front vector. The problem is the tractor can't more sideways (at least for long). So once there is torque/ lack of alignemnt, the system can't be stabilized (depending on constraints).
     
  7. Saxxon

    Saxxon Member

    Joined:
    Nov 15, 2017
    Messages:
    7
    Location:
    Brighton, CO
    It may reduce the incidence of jack knifed rigs, but there are times you can't stop it. I was driving south out of Cheyenne, WY one morning with an inch plus of ice on the road, and gusting winds slamming the truck in the side. It was like driving thru a corridor with all the rigs laying on their sides off the road.

    A gust of 50+ mph hit the truck, put me in an immediate 30 degree jackknife. The only reason I didn't wreck was I had an empty trailer, and a lot of experience screwing around in a raid yard skidding intermodal chassis in a dirt lot in deliberate skids (you get it whipped sideways and dust the guy parking in the lot). The truck went thru 4 cycles of left to right jack knife as I fought to get it under control sliding down the slight grade. Finally got it centered thru the oscillations and almost stopped - I'd only been doing 25-30mph when it started.

    Now the automatic steering and power controls might have made it easier, or it might have made it worse because of the confluence of factors. My driving background certainly gave me an edge, but the maintenance crew searched in vain for the missing seat cushion when I got back to Denver.
     
  8. RamgeRover

    RamgeRover Member

    Joined:
    Jul 30, 2016
    Messages:
    49
    Location:
    Palm Springs, CA USA
     
  9. Sunshine State

    Sunshine State Automotive Enthusiast

    Joined:
    Jul 13, 2017
    Messages:
    1,305
    Location:
    Florida
    #29 Sunshine State, Nov 22, 2017
    Last edited: Nov 22, 2017
    Although I don’t drive a tractor trailer frequently anymore l do have a Class A CDL with lots of miles of experience with oversize and heavy loads plus I own a heavy equipment company. One of the last things a truck driver with any experience has on his mind is jack knifing and if Tesla did any research they know this also. Not that jack knifing can’t happen, but it isn’t the problem they try to make it sound like(claiming driver nightmares). Maby Tesla can also address over the road driver wife infidelity too. That leads me to believe that Tesla is talking about Jack knifing for PR with car drivers that have no truck experience. Another disorienting feature of the Tesla design is the center driving position which puts the driver further away from the driver side mirror which an experienced CDL driver relies on. I recently drove a 40’ high end motor home, while being a significantly smaller and lighter vehicle than what I have great experience driving, it felt very odd because it had a sightly further distance to the drivers mirror, no where near the center position of the Tesla truck. If Tesla was serious about building a truck that would be accepted rather than a PR exercise or distraction they would build a truck with the refined design of today’s trucks that works and use the electric drivetrain if they think that the EV drivetrain could be a serious improvement. Already some big fleets that buy trucks by the 10’s of thousands have committed to a handful of Teslas to get the virtually free PR (by comparison to what they buy).
     
  10. electracity

    electracity Active Member

    Joined:
    Jun 8, 2015
    Messages:
    4,028
    Location:
    60606
    LCD screens can provide images far superior to mirrors. Cameras can do light amplification. Vehicles around the truck can be tagged. The exact location of vehicle relative to the end of the trailer can be displayed.

    There is no aspect of situational awareness that can't be made better with the tech Tesla is using. The only problem will be that experience drivers will have to change well established driving behaviors.
     
  11. Sunshine State

    Sunshine State Automotive Enthusiast

    Joined:
    Jul 13, 2017
    Messages:
    1,305
    Location:
    Florida
    I’ve seen mirrors crack but not fail, I think that’s why DOT doesn’t allow trucks to be driven without them. (Cameras are not allowed as a replacement) Its a bit like bureaucrats getting involved with something they know nothing about because they think they know better
     
  12. electracity

    electracity Active Member

    Joined:
    Jun 8, 2015
    Messages:
    4,028
    Location:
    60606
    Perhaps you could keep the tractor parallel to the trailer, but that doesn't prevent the whole rig from sliding sideways. This trades a jacknife for a roll over. The bigger problem isn't jackknifing. It's keeping truck and trailer parallel to the direction of travel.
     
  13. electracity

    electracity Active Member

    Joined:
    Jun 8, 2015
    Messages:
    4,028
    Location:
    60606
    I've seen heated mirrors stop working and become unusable.
    Tesla will probably design a vision system that will have some redundancy. For example, camera images can be displayed on either LED screen. A truck with a broken camera will still have ultrasonic sensors.

    A good aspect is that Tesla has to make all sensing and display ultra reliable for all vehicles. None of these issues apply to only the semi.
     
  14. Sunshine State

    Sunshine State Automotive Enthusiast

    Joined:
    Jul 13, 2017
    Messages:
    1,305
    Location:
    Florida
    You may be missing my point that actual physical mirrors are required by law, because they are so simple and reliable. I love technology. I drink water and could stop that and go on an IV drip but the water works really well for me and is simple;)
     
  15. mongo

    mongo Well-Known Member

    Joined:
    May 3, 2017
    Messages:
    12,857
    Location:
    Michigan
    Text from : 49 CFR 571.111 - Standard No. 111; Rear visibility.

    Mirrors are required by law for the following stated reason: " S2. Purpose. The purpose of this standard is to reduce the number of deaths and injuries that occur when the driver of a motor vehicle does not have a clear and reasonably unobstructed view to the rear."

    And the law was written before camera and display tech was were it is now.

    Mirrors are also wasteful or energy at highway speed.

    For trucks, the requirement is
    "S8.1 Each multipurpose passenger vehicle and truck with a GVWR of 11,340 kg or more shall have outside mirrors of unit magnification, each with not less than 323 cm 2 of reflective surface, installed with stable supports on both sides of the vehicle. The mirrors shall be located so as to provide the driver a view to the rear along both sides of the vehicle and shall be adjustable both in the horizontal and vertical directions to view the rearward scene."

    Interestingly, although trucks don't reference the backing event, there is no requirement I see in the testing that says you can't auto fold the mirrors when moving forward. So until regulation change, both could be used to achieve legality and efficiency.

    "
    Backing event means an amount of time which starts when the vehicle's direction selector is placed in reverse, and ends at the manufacturer's choosing, when the vehicle forward motion reaches:

    (a) a speed of 10 mph,

    (b) a distance of 10 meters traveled, or

    (c) a continuous duration of 10 seconds.
    "
     
  16. boki

    boki New Member

    Joined:
    Apr 25, 2018
    Messages:
    1
    Location:
    abracadabra
    I agree with
    etna,
    evanlin: "It's only a problem that "can't slow down enough and hit front obstacles",
    jr4488 "An experienced driver allows leaves enough room and keeps the speed low enough to pull the trailer straight in an emergency."

    My full comments on this are here (Tesla Semi suggestions? | Tesla).

    "
    I would say 'impossible jacknifing' is- detecting onset and then automatically correcting it properly/optimally: steer into the skid (prevent driver's over steering), release tractor brakes (max brake but not lock up, abs), use independent traction control of each drive wheel to help straighten the tractor. The reason I think they can't (yet) prevent the onset is because they don't know exact traction (varies 10x from dry to icy road). If driver brakes and locks brakes on a slippery road, and trailer is at an angle, the onset will happen. Corrective action will help if jackinfing is the only problem and there is enough room ahead. And I think it would be useful to perfect this, if possible.

    Sometimes truckers will jacknife their truck on purpose if their brakes fail in order to stop, or if there is a greater hazard ahead. So I don't think it is good idea to make it 'impossible' for those reasons.

    If you go too fast on a black ice and you don't jacknife, it can take you forever to come to a stop. But you also don't want jacknife and to go off-road.

    So my thought was that only proper way is prevention. And if we had exact knowledge of traction, along with other easily obtainable data, it is possible. So I think it would boil down to R&D of traction. The perfect solution could be: for a given vehicle (dims, weight, load, known tire/road friction), given the speed of travel, determine maximum safe stopping (following) distance without jacknifing onset. Or for a given stopping (following) distance, give maximum safe speed without onset of jacknifing. That is how I would formulate the task. I am open for any inputs.
    "
     
  17. beachbum77

    beachbum77 Banned

    Joined:
    Jun 22, 2017
    Messages:
    887
    Location:
    Hot & humid Florida
    Mongo

    No matter what the Tesla Semi is equipped with you will notice on the recent photos and videos that the big Silver rig now has side mirrors that were not installed at the unveiling. Laws trump technology every time. Until all trucks have cameras, etc. you can expect the mirrors to be required.
     
  18. mongo

    mongo Well-Known Member

    Joined:
    May 3, 2017
    Messages:
    12,857
    Location:
    Michigan
    Yah, I was providing the law that requires the mirrors for reference. Until FMVSS is updated to allow cameras, the mirrors will be required equipment.
     

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC