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Thread: Unrealistic AI Train Speed!?

  1. #11
    Join Date
    Nov 1999
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    It's actually far more complicated then just resources.
    There are a number of problems with the physics which made it necessary to set up overrides.

    One of the major problems is wheelslip. Wheelslip occurs per engine but is not reported at train level. A player runs the engine and gets the wheelslip warning if things go wrong. But AI trains are controlled at train level, and at that level there is no wheelslip report. So, engines in a train can start slipping without the AI control ever knowing about this, which results in serious loss of tractive effort and could even stall the train. This is particularly a problem for consists of Multiple Units and push-pull sets, as the driving trailers (cab cars or whatever you want to call them) are defined as engines but ofcourse have a very low weight and therefor are very prone to slipping.
    Another problem is the pretty large variation in controls and control reaction. Some engines need a full 100% throttle to even start moving, others shoot off like a rocket at just 10% or so. The same applies to brake control - some trains hardly react until brakes are applied at 25% or more, others just need 1%. When running the train as player one is often familiar with these characteristics, but AI control, ofcourse, cannot easily distinguish these differences.
    So AI control does try to apply proper physics (not the full player train advanced physics but a more basic setup), but to ensure proper control there are overrides. If a train does not react quickly enough to the applied controls, AI control takes over and applies standard acceleration or brake rates.
    It would perhaps be possible to have a more sophisticated control with regards to acceleration and maximum speed. It would require better wheelslip handling and a more 'patient' override control. But I would strongly suggest not to meddle with the brake overrides as that is very likely to cause problems with trains not stopping in time for stations and signals.

    Some time ago (well, years ago, actually) I did some tests, removing the acceleration overrides. It did work for some trains but there were quite a number of trains which never got up to proper speed, sometimes slowing down to just 15 mph on gradients where as the same train could easily maintain linespeeds upto 80 mph when driven as player train. In all cases, the problems were caused by wheelslip.

    Regards,
    Rob Roeterdink

  2. #12
    Join Date
    Nov 2011
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    California, USA
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    Very useful information, Rob. Thanks for chiming in.
    Ryan
    US-based railfan and programmer. Author of various timetables and safety scripts for Open Rails.

  3. #13

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    Interesting! Thanks!

    The problem now is to try to determine approximate "realistic" speeds for AI trains. The speeds will vary according to whether the trains run on the flat, go up hill, and go down hill. One way is to drive AI trains under the wanted conditions and note the maximum speeds, and then edit the AI trains consist file and/or the Default performance under MSTS AE. This is a slow process. Plus the determined speed is only realistically applicable for AI trains under the conditions it was tested under (on the flat, up hill, or down hill). Since AI trains speed remains about constant regardless of the terrain it runs under, it becomes difficult to simulate AI train speeds over varying terrains.

    One way around this is to create AI trains with set speed limits (set under consist file, and/or under the AE) for each of the varying terrains. So one AI train only runs on the flat, the other AI train only runs up hill (at set grade), and the other AI train only runs down hill (at constant grade). The AI trains are exactly the same consist, the only difference is their maximum speed settings (for various terrains).

    Again a lot of extra work creating more realistic AI train speeds!

    Sigh!!!

  4. #14
    Join Date
    Nov 2011
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    Indeed, it's quite frustrating.

    In the far future, when Open Rails gets its own path format, perhaps we could add a special speed instruction that changes the AI's target driving speed when it reaches a specific point. Well, one can dream...
    Ryan
    US-based railfan and programmer. Author of various timetables and safety scripts for Open Rails.

  5. #15
    Join Date
    Feb 2013
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    Quote Originally Posted by rman View Post
    Indeed, it's quite frustrating.

    In the far future, when Open Rails gets its own path format, perhaps we could add a special speed instruction that changes the AI's target driving speed when it reaches a specific point. Well, one can dream...
    That's an intriguing solution...using the AI path to provide speed control. Maybe in the next ten years.
    Cheers, R. Steele [Gerry] It's my railroad and I'll do what I want! Historically accurate attitude of US Railroad Barons.


  6. #16
    Join Date
    Oct 2004
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    Onalaska, Wa
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    Quote Originally Posted by rman View Post
    Indeed, it's quite frustrating.

    In the far future, when Open Rails gets its own path format, perhaps we could add a special speed instruction that changes the AI's target driving speed when it reaches a specific point. Well, one can dream...
    As in being able to set an AI train should only be able to travel a certain percent of the postes speed limit of the posted track speed?

    Sent from my SM-G988U using Tapatalk

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