Class 47 Physics

Discussion in 'TSW General Discussion' started by ghawk2005, May 21, 2021.

  1. ghawk2005

    ghawk2005 Well-Known Member

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    I have got hold of some real life data timings from 1985 via RailPerf society and have done multiple tests and comparisons in the game with 8 Mk2s and very impressed to say that at each milepost the TSW2 is within 1mph either side. 1mph quicker up to about 90 and then no more than 1mph slower at the very top end.

    Given the huge variation with real life stock I would say this is a pretty good effort. Very happy with this. The model looks and sounds amazing and to know the acceleration is bang on. I can now really enjoy it. Shame they haven’t fixed the brake creeping on bug if you accidentally hit ‘Release’ though. (But at least I can drive it can be very careful to not hit release). I also LOVE the way it bounces around and the coupling and air pipes aren’t static too. Love suspension bounce and cab sway.

    Well done to all those involved.
     
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  2. Tonto62

    Tonto62 Well-Known Member

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    Great! They've fixed the sounds so that the wheels make some noise as they pass over the track? I'll enjoy driving that later, the engine sounded excellent last time I drove one, the wheels were completely silent however. Can't wait to try it out.
     
  3. Purno

    Purno Well-Known Member

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    I'm avoiding driving the Class 47 Blue until they have fixed the brake creeping. That bug is too annoying and takes away my enjoyment from the loco.

    Thankfully the Class 47 Green still works fine.
     
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  4. Tonto62

    Tonto62 Well-Known Member

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    The brake problem is annoying but I've learnt to be very careful not to go into release. The lack of running sounds spoilt it for me though so I hope they've fixed it.
     
  5. KiwiLE

    KiwiLE Well-Known Member

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    The "brake creep bug" is an item I have commented on before but would like to know if the RL mechanics are at play, and the bug isn't actually a bug...
    When you put the train brake into 'release', it overcharges the brake pipe to 78 psi to alleviate sticking brake cylinders, etc and this was used to normalise the train brake to 72.5 psi.

    If we needed to overcharge the train brake, this was held for 1 minute, and then didn't touch the train brake again for another 4 minutes, allowing the overcharge to bleed away, the train brake settling back to 72.5 psi running pressure. If a brake application had to be made within the 4 minutes, then the exercise was repeated from the beginning, or the brake creep would happen.

    I assume this is modelled in simugraph, so the only 'bug' is it's too easy to put the brake handle into this overcharge position?
    Vacuum braked wagons were overchargable too.
     
  6. Tonto62

    Tonto62 Well-Known Member

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    I think the problem was that even if you followed the correct procedure the brakes still crept back on.
     
  7. stujoy

    stujoy Well-Known Member

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    The brake creep is most definitely a bug. It can actually occur if you don’t ever go into release. It definitely will happen if you go into release for one nanosecond. The issue cannot always (in fact very rarely can) be resolved using the correct method used to resolve it in real life. The brakes will creep back on. As strange as all of that, the issue can sometimes resolve itself without any actions taken to resolve it.

    Otherwise, the loco is excellent, as stated in the OP’s post.
     
  8. KiwiLE

    KiwiLE Well-Known Member

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    Ah ok, rip. :(
     
  9. Purno

    Purno Well-Known Member

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    Indeed. Apart from the fact that it may be a tad too easy to get into the overcharge / brake creep situation, the bigger problem is that there's no way to get out of the sitution once you got into it.

    And even if it were possible, I think the whole situation would confuse quite a few people and a decent tutorial explaining how this all works would be appropiate.
     
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  10. ghawk2005

    ghawk2005 Well-Known Member

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    I don’t understand why DTG said they’d practically fixed the bug but haven’t released the updated fix! Crazy. It could do with better run sounds and brake rub too but I doubt that’ll happen now.
     
  11. cwf.green

    cwf.green Well-Known Member

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    Agreed. Just think if this was prototypical behaviour. Basically you'd grind down the brakes/wheels in no time.

    EDIT: By the way. I do remember that excluding this bug the Class 47 seems to behave very realistically. In general it seems as if DTG usually does a very good job with the physics of UK stock. At least in terms of EMU/DMUs. The Class 377 was in TSW2020 nearly 100% accurate in terms of brake physics. I can't remember if the acceleration times were correct but I think they were?

    They temporarily screwed up the brakes in TSW2 preserved collection for ECW but they seem to have fixed it for SEHS.
     
    Last edited: May 21, 2021
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  12. ghawk2005

    ghawk2005 Well-Known Member

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    They haven’t fixed the acceleration profile for the 166 which is a massive shame. But most other stuff is pretty good
     
  13. cwf.green

    cwf.green Well-Known Member

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    ghawk2005 I noticed your thread mentioning this. I haven't had time to check any UK stock except the Class 377 and the Class 37, so I can't speak accurately about their, um, accuracy.

    For any player interested (or DTG), the brake characteristics of UK rolling stock is quite well defined and well publicised. Formulas for calculating retarding brake force (i.e. the force which decelerates a vehicle) from the so called "equivalent brake force" (the brake "force" value printed on the TOPS panel on locos or available for wagons for each TOC). The theory/formula can be found in group standards document GMRT2045.

    The theory behind this conversion is almost identical to the ones used by UIC.

    F_retard = EBF * 1.275,

    where EBF = equivalent brake force, and the number 1.275 is the product of the gravitational acceleration and the mean coefficient of friction in the speed interval tested. Again, like for mainland European trains, the equivalent brake force is given as a weight (tonnes) which when multiplied by the gravitational acceleration yields a force. This force is the normal force caused by the brake pad pressing on the tread and which yields a friction force (thus the coefficient of friction multiplier) that decelerates the wheel.

    The convention of expressing forces as weights is idiosynchratic and archaic but you could think of it as the equivalent force caused by a mass pressing down, vertically, on the wheel tread.

    The great thing about this formula is that if you have the full function for the coefficient of friction dependence on the velocity you simply need to know the EBF and then you have the retarding force for any velocity. If you don't have this CoF known then you can infer it from the average deceleration (either measured in velocity / time or deduced from the stopping distance s = v*t_application/2 + v^2/2a, a = average deceleration).

    Obviously the stopping distances produced by all these variables should be verified against driver input to prevent garbage-in-garbage-out errors.
     
    Last edited: May 21, 2021
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  14. ghawk2005

    ghawk2005 Well-Known Member

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    Thank you for this, Very helpful.
     

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