Slack and yank?

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  • Heruraha93
    Senior Member
    • Dec 2019
    • 139
    • Melbourne, Australia

    #1

    Slack and yank?

    Hi sorry I am still not up with all the train terms and so am just wondering what Slack and yank actually mean in say OR or real life for that matter - I had thought it related to if a train starts too fast or a sudden acceleration, but is this right? And can it happen in OR - when I play I never find that my engine ever starts too fast, everything is always gradual and if I happen to start to fast then wheel slip stops me - I am not deliberately wanting coupler breaks but I have been reading other players experiences in OR and Run8 and it does sound exciting to have to deal with the challenge of possible breaks .
    Also I am hardly an experienced engineer so I would anticipate making mistakes - which I think is a big part of the appeal of Sims - train, racing and flight Sims especially - that one can progressively get better, so if I am driving and not having any breaks happen, I presume I am doing a good job yes? Or does it depend on the train set and it's properties?
    I read another post from a while back where someone was unable to climb a grade with a train simulations trainset on a route despite to their knowledge such a climb from 0.8% being possible and one comment was that some 3rd parties just aren't familiar enough yet with OR- so it does depend on the trainsets?
  • Vince
    6500 Post Veteran

    • Nov 1999
    • 6961
    • Mohave

    #2
    The 'Why of Slack'

    I asked a Union Pacific engineer "How do you start a heavy, 10,000 ton, train." Her answer was "One car at a time." So in real world rail operations, that is the reason for slack.
    There have been some discussions at Elvas Tower regarding how OR handles slack.

    I watch a lot of cabride videos. Tram rides through the citys of Europe also has me hooked!
    That being said that the absolute longest freight consist I've seen in all Europe railroads cab ride videos (youtube) was 45 wagons with most having 25 to 30 wagons.
    The reason is simple. the couplers have NO slack at all. Thus starting tonnage usually runs about 1000 to 3000 metric tons as some videos publish consist specs. Quite interesting.
    The 3000 ton is pure speculation from when I observed two electrics pulling 11 tankers.

    Some links:
    Freight: https://www.youtube.com/watch?v=eb6fV5eyjp8
    Tram: https://www.youtube.com/watch?v=MoPBANJY_qA
    Freight: https://www.youtube.com/watch?v=QCx9Qa7ZRUE
    Tram Incidents: https://www.youtube.com/watch?v=mshJ7L3VGj8

    Enjoy,
    ............Vince ..............
    ...... Author NECv4 .......
    .... LIRR BUILD PHOTOS ....
    ...... Eschew Obsfucation ......

    On the The Statue of Liberty in New York Harbor there is a Tablet. On it is written:
    "Give me your tired, your poor, your huddled masses yearning to breathe free,
    the wretched refuse of your teeming shore, send these, the homeless, tempest-tossed to me,
    I lift my lamp beside the golden door!"

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    • derekmorton
      5500 Post Veteran



      • Nov 1999
      • 5699
      • Eltham, Victoria, Australia.
      • ORTS

      #3
      >unable to climb a grade

      We have a thing called a "ruling grade load" for each hill and each engine.
      When you build a train you have to take into account, grade and speed.
      Passenger trains typically have 5 - 10hp/tonne.
      Freight trains can have 1/2 - 5hp/tonne.

      Slack is the amount of gap in the coupler when done up.
      When you have 200 cars the slack can be 6 feet or more if the couplers are well worn.

      Comment

      • Heruraha93
        Senior Member
        • Dec 2019
        • 139
        • Melbourne, Australia

        #4
        oh my - wait 6 feet? what does even look like? i am still learning about the different couplers out there - how is that possible? is that for some kind of loose coupling?

        Comment

        • seagoon
          5000 Post Veteran

          • Jun 2001
          • 5161
          • Yamba, N.S.WALES, Australia

          #5
          Originally posted by Heruraha93
          oh my - wait 6 feet? what does even look like? i am still learning about the different couplers out there - how is that possible? is that for some kind of loose coupling?
          That is six feet over the full length of the 200-car train.
          IBM XT i386; 512Kb RAM; 5.25" FDD; 1.4Mb FDD; 5Mb HDD; VGA 256-colour graphics card; AdLib soundcard; DR DOS 6.0; Windows 3.0

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          • Heruraha93
            Senior Member
            • Dec 2019
            • 139
            • Melbourne, Australia

            #6
            ah right okay that makes more sense, i was thinking 6 feet between cars which seemed crazy to me but then i am not up with all the ways waggons get coupled.

            Comment

            • roeter
              Senior Member
              • Nov 1999
              • 171
              • Netherlands.

              #7
              Originally posted by Vince
              The reason is simple. the couplers have NO slack at all. Thus starting tonnage usually runs about 1000 to 3000 metric tons as some videos publish consist specs. Quite interesting.
              No, it isn't. There's plenty of slack in the couplers. A far more practical reason for the max. length of freight trains is the general length of yards and sidings. Because of the high frequency passenger services, freight trains are often held in sidings and loops for many times during their full run. Obviously, you don't want freight trains which are longer than these sidings. Many shunt yards, most of which date back to early steam days, also have limited length. That's what sets the maximum length for freight trains (about 35 4-axle wagons here in the Netherlands, for instance).

              Regards,
              Rob Roeterdink

              Comment

              • ragtimer
                2000 Post Veteran
                • May 2005
                • 2009
                • Stalinist,broke United Kingdom (Hey buddy,can you spare �1.3 trillion?))

                #8
                Search mendip rail jumbo trains.When I was driving trains,we had a train of maybe 30 odd loaded PGA wagons fitted with instanter couplings.I would estimate the slack would be 15 to 20 feet which required very careful handling to avoid broken couplings and "snatches".

                Comment

                • scottb613
                  2500 Post Veteran


                  • Apr 2003
                  • 2848
                  • Downeast Maine (soon)
                  • ORTS

                  #9
                  Hi Folks,

                  I think Peter started work on coupler slack in ORTS but I don't think it's done... While we have the animation modeled - the physics don't seem to be there - as the locomotive must overcome the friction of the entire train to start it moving - as opposed to the "one car at a time" as mentioned above... I've done some pretty comprehensive testing and reading on steam trains - the controlling friction limiting the length of a train should be the friction between 5 MPH and 10 MPH - not the startup... In ORTS it is definitely the startup...

                  Regards,
                  Scott
                  <a href=https://www.trainsim.com/forums/filedata/fetch?filedataid=80663&type=full title=thumb_80663.png >thumb_80663.png</a>​ My Blender Models

                  Comment

                  • baldwin
                    6000 Post Veteran


                    • Nov 1999
                    • 6358
                    • Chippenham, Wiltshire, UK.
                    • ORTS

                    #10
                    There is slack in the couplings in OR, but it is minimal and gives the impression of having none on starting. Once rolling, slack action can be observed along the train under braking and acceleration
                    Beer is not a matter of life or death, it is much more serious than that.

                    Comment

                    • Heruraha93
                      Senior Member
                      • Dec 2019
                      • 139
                      • Melbourne, Australia

                      #11
                      thanks for this information Scottb613 and Baldwin sorry to ask for clarification but what though does this mean in simpler terms:

                      "the controlling friction limiting the length of a train should be the friction between 5 MPH and 10 MPH - not the startup... In ORTS it is definitely the startup..."

                      Comment

                      • scottb613
                        2500 Post Veteran


                        • Apr 2003
                        • 2848
                        • Downeast Maine (soon)
                        • ORTS

                        #12
                        Hi...

                        The bottom line is - the startup friction of a train should be irrelevant - as you are starting the train a single car at a time - it's the friction when traveling at a slow speed with the full weight of the train behind you that should stop you if you've exceeded the capacity of the locomotive... In ORTS - if you can start a train you can pull a train - given a constant grade without introducing of new variables...

                        Whether right or wrong - these are the conclusions I've drawn from this series articles and my own testing of ORTS...

                        Freight Train Resistance and Tonnage Ratings
                        Part 1)


                        Part 2)


                        Part 3)


                        Your mileage may vary...

                        Regards,
                        Scott
                        <a href=https://www.trainsim.com/forums/filedata/fetch?filedataid=80663&type=full title=thumb_80663.png >thumb_80663.png</a>​ My Blender Models

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                        • mikeebb
                          Senior Member

                          • May 2010
                          • 989
                          • Pacific Time
                          • ORTS

                          #13
                          In very early betas of ORTS (before 1.0), slack was explicitly modeled, and was reported in the F5 HUD. That vanished at 1.0 and later. Not sure if it was modeled correctly, but you could see it in the HUD being pulled out on starting (by car or groups of cars in the debug HUD), and running in again when the throttle was closed and dynamics applied (and being controlled with train air). It vanished from the HUD in 1.0, and I'm not sure if it's still modeled the same way. Perhaps it wasn't done correctly, or introduced things that the physics otherwise couldn't handle. Might be interesting if some old heads in the project could think back on it and discuss.

                          Edit: even MSTS had some modeling of slack. To check, set the view to the last car of a reasonably long train, release the brakes, and start. The locomotive (in MSTS and, I'm pretty sure, ORTS) will start some time before the caboose jerks into motion.

                          Comment

                          • R. Steele
                            3500 Post Veteran

                            • Feb 2013
                            • 3928
                            • known universe
                            • ORTS

                            #14
                            Originally posted by scottb613
                            Hi...

                            The bottom line is - the startup friction of a train should be irrelevant - as you are starting the train a single car at a time - it's the friction when traveling at a slow speed with the full weight of the train behind you that should stop you if you've exceeded the capacity of the locomotive... In ORTS - if you can start a train you can pull a train - given a constant grade without introducing of new variables...

                            Whether right or wrong - these are the conclusions I've drawn from this series articles and my own testing of ORTS...

                            Freight Train Resistance and Tonnage Ratings
                            Part 1)


                            Part 2)


                            Part 3)


                            Your mileage may vary...

                            Regards,
                            Scott
                            Good resource source, thanks Scott, Regards, Gerry
                            Cheers, Gerry
                            "A mind is like a parachute. It doesn't work if it is not open." Frank Zappa
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                            • scottb613
                              2500 Post Veteran


                              • Apr 2003
                              • 2848
                              • Downeast Maine (soon)
                              • ORTS

                              #15
                              Originally posted by R. Steele
                              Good resource source, thanks Scott, Regards, Gerry
                              Hi Gerry,

                              Happy to help - while we deal with different era’s we seem to be working towards the same goals...

                              LOL - this is what I get for perusing century old books that Dave occasionally links on Elvas... While the data is old the laws of physics should remain the same...

                              What started me down this path is my steam locomotives “seem” to have difficulty pulling trains of similar lengths I see documented in photographic evidence from the era (granted there’s much unknown in photographs) - which would make sense if when I start I’m fighting the resistance of an entire train instead of each car in turn...

                              Regards,
                              Scott


                              Sent from my iPad using Tapatalk
                              <a href=https://www.trainsim.com/forums/filedata/fetch?filedataid=80663&type=full title=thumb_80663.png >thumb_80663.png</a>​ My Blender Models

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