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Thread: Davis values

  1. #11
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    Quote Originally Posted by dcarleton View Post
    Please do tell -
    Some of us have just spent months creating OR folders with OR eng and wag files that use Davis values, with the eng files also referencing the set of inc files created by Jerry Storey. Are we going to have to revise all that?
    AFAIK the "changes were made to how power was calculated in the diesel model for OR" mentioned by Steamer_ctn are "behind the scenes"..they do not affect how the OR diesel engine definition is used.
    All the data in those files --- [VER2 Standard ORTS Diesel Engine] --- should still be applicable.

    If Peter visits this thread again, perhaps he can affirm or correct this statement?... or some other OR Developer team member?

    https://www.trainsim.com/vbts/showth...NG-FILES-ver-2
    Last edited by R. Steele; 09-22-2020 at 05:29 PM.
    Cheers, Gerry
    It's my railroad and I'll do what I want! Historically accurate attitude of US Railroad Barons.
    Forever, ridin' drag in railroad knowledge.


  2. #12

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    Quote Originally Posted by R. Steele View Post
    If Peter visits this thread again, perhaps he can affirm or correct this statement?... or some other OR Developer team member?
    Gerry is correct that the changes were in the back end of OR.

    The rest is up to ensuring that input data is correct for each locomotive, etc.

    The point that I was making is that provided good quality information is available, it is possible to match the real life scenario reasonably closely.

  3. #13
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    Keep in mind the Davis formula doesn't apply to speeds under 5mph. Never has.

    Another issue is that FCalc ISN"T the Davis formula... it's slightly tweeked to put it a bit closer to KUJU's Friction() values. Typically you can get numbers out of FCalc that are with 1 to 1.5% of the Davis formula but in the low speed range it's off by twice that. FCalc's numbers subtracted from straight Davis calculations s, will produce a horizontal S curve... a bit higher at slower speeds, definitely lower at higher speeds (often a lot lower). I don't use FCalc; I have the Davis formulas in a spreadsheet and I calculate the data for .wags there.

    Last thought is I never assume any values offered up in any .wag file I've downloaded have any basis in reality. Every car I put into running condition will have most of it's parametric values replaced (late steam era only).
    Dave Nelson

    Seldom visiting, posting less often that that.

  4. #14
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    ...and I was aware of that limitation of FCalc2 when I choose it to calculate the Davis values for all the OR conversions I've released. I thought most people could get FCalc2 and very few would have access to a true Davis calculator. By the way, on another subject, the CurtiusKnuiffler numbers that are in the Standard Engine files are from a Joe Realmuto's CurtiusKniffler calculator, permission given to include them with the appropriate OR engine definitions.

    I've been slowly changing my FCalc2 Davis values over, most of the time I do not notice any difference...anyway, the detail to remember is to check all your stock's values -- as Dave suggests, and to use good quality data as Peter suggests. Do those two things and you'll get better performance from OR.
    Cheers, Gerry
    It's my railroad and I'll do what I want! Historically accurate attitude of US Railroad Barons.
    Forever, ridin' drag in railroad knowledge.


  5. #15
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    Gerry, IIRC there are three distinct versions, each ties to a date. The original is something like 1926, the next was, IIRC 1970 and the third was a few years after that. And of course there are variations in each for different types of cars or wheel bearings.

    The formulas I used were found on (Austrailian) Peter's Coals site and I plugged them into excel along with a bunch of other variations so it would produce a .wag file. I believe I sent you a copy. If you still have it then you can ferret out the 1920's formulas.
    Dave Nelson

    Seldom visiting, posting less often that that.

  6. #16
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    (My below comments are all in the context of using "roller" type bearings in the OR code)

    As for as Mullan goes: The decision for us to NOT use the Davis formula friction block was, in fact, because of the fact that when we did use the Davis block, it created what we (the TrainSimulations team) perceived as unrealistically high starting friction forces (0 to 5 MPH). The Davis equation itself may be performing fine, but the fact is that for whatever reason, at speeds below about 5 MPH, the OR code uses some other linear equation to ramp the friction up. Going off memory here, I believe we noted that when starting a loaded coal train from a stop on the 2.2% at Austin on Mullan Pass, each car was seeing in the neighborhood of 2,000 lbs of friction, vs. I think about 1/4th of that when using the older MSTS friction block. The huge starting friction forces made it virtually impossible to start a prototypical train consist without breaking couplers. It should be noted that Mullan is a place where coupler forces are pushed to the max in real life, but they still manage to start heavy unit trains from a stop on this grade on a routine basis. Couplers break, but often that is a result of poor train handling and/or coupler knuckles that have already been weakened due to other factors.

    As far as I know, the additional resistance at 0 MPH in the OR roller bearing friction code (which ONLY goes into affect when using a Davis block) was based on an AREMA claim that roller bearing resistance is significantly higher at a stop. Peter, I believe I emailed you some AREMA manual excerpts from a recent AREMA manual where this statement has been changed to say that with roller bearings, there is "little or no" additional resistance when starting from a stop. This is certainly NOT true with solid bearings (aka "friction bearings").

    At any rate, I'm assuming that the 5 MPH transition point between the starting resistance equation and the Davis equation is not based on any real research, but instead on one of the OR coder's generic interpretation of what "low speed" means.
    ~Sean Kelly~

    MRL Mullan Pass for ORTS
    https://www.trainsimulations.net/Pro...LLAN_ORTS.HTML

  7. #17

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    Instead of using ORTSBearingType or MSTS friction settings you can also use ORTSStandstillFriction and ORTSMergeSpeed for those values respectively; in the case of using Davis values.

  8. #18
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    I am not to well versed on these 2 settings I just know most of the trains in Mullan Pass are very hard to even start. The snow one being the worst I have tried everything I could to get it to move but the train just will not get over 10 MPH. I know it must be something I am doing wrong but I have tried everything I know.

    So what is the secret to get this massive train to even move properly.

  9. #19
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    Hi Michelle,

    I just tried the 2 snow activities and they both move in notch 1, I didn't try the top speed.

    Did you apply the settings as supplied by TS?
    What version of OR?
    Can you post a log file of a run please?
    Cheers
    Derek

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