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Thread: Is there a way to make steam locomotives wheel slip briefly as they start a train?

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    Default Is there a way to make steam locomotives wheel slip briefly as they start a train?

    Hey all. I was wondering if there was a way to make steam locomotives wheel slip briefly and at random when starting a train. Here's an example video to illustrate what I mean: (https://www.youtube.com/watch?v=MQKbwiRZ7fY)
    It's kinda unrealistic to have them perfectly start every train they attempt

    Also on articulated locomotives like the 4-6-6-4 Challenger and the 4-8-8-4 Big boy, it's possible for one set of wheels to have perfect traction while the other one is slipping, but that never seems to happen in this game.

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    I can remember a time in the "early days" when some locos did that all the time and the posts in these forums were on how to stop it from happening.

    Seriously, it sounds like you would need some skills in scripting and possibly animating as well. Both are beyond my pay grade.
    TRS19 Platinum Edition SP2 build 110491

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    I have seen it happen on some of SLW's newer German and Polish steam loco models. I only use DCC control but if I have gone straight to full power (or close to it), I have seen the wheels slipping, and you need to back off the power to stop it.

    Hope this helps.

    Cheers,
    Piere.

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    Quote Originally Posted by pware View Post
    I can remember a time in the "early days" when some locos did that all the time and the posts in these forums were on how to stop it from happening.

    Seriously, it sounds like you would need some skills in scripting and possibly animating as well. Both are beyond my pay grade.
    On the good old times we could see sparks at the wheels on some locos. I can't believe these amenities had to be eliminated so other "improvements" could be made. Obviously we are missing something here and there..

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    Generally, to achieve wheel slip with any loco, one must exceed the limit of adhesion between wheel and rail.

    Open the throttle too far for conditions and you should get wheel slip.

    This works in T:ANE with the C&O Kanawha, on a realistic clone of Thurmond Empties. (Set for cab control and Cinematic Camera unlocked.)

    Many Trainz diesels provide a nice wheel-slip screech under both acceleration and dynamic braking.

    :B~)

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    That might be why I'm not seeing any wheel slip. I use a lot of A.I. I'm guessing they're too good at driving the steam locomotives to make them slip. Kinda makes me wonder what would happen if you installed ATC in a steam locomotive.

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    Quote Originally Posted by janathan View Post
    That might be why I'm not seeing any wheel slip. I use a lot of A.I. I'm guessing they're too good at driving the steam locomotives to make them slip. Kinda makes me wonder what would happen if you installed ATC in a steam locomotive.
    Yeah, well, the AI drivers cheat anyway, if you watch closely. Try to emulate their acceleration you'll get wheel slip a lot.

    Driving a teakettle is an art, not a science!

    :B~D

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    Quote Originally Posted by RHKluckhohn View Post
    Yeah, well, the AI drivers cheat anyway, if you watch closely. Try to emulate their acceleration you'll get wheel slip a lot.

    Driving a teakettle is an art, not a science!

    :B~D
    They essentially use DCC mode. Under DCC control you dial in a speed from 0 to maximum as set in the espec. The game engine uses the accel and decel tags plus train mass to determine an acceleration to use to change to the new speed. No wheel slip, no calculating resistance forces, no calculating tractive force at rail - not real physics involved. For steam locos it's a bit more complicated since TE available is not simply interpolated from curves of TE vs speed and throttle setting as supplied by the espec. That simplicity is for diesels, electrics and other forms of motive power.

    AI doesn't cheat it just plays a different game like anyone else who uses DCC control.

    Bob Pearson
    Last edited by RPearson; December 1st, 2020 at 06:50 PM.
    TRAINZ-UTC-TRS04-TRS06-TC1&2-TC3-TS09-TS10-TS12-TANE(TEG)-TMR17-TRS19
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    Quote Originally Posted by janathan View Post
    Hey all. I was wondering if there was a way to make steam locomotives wheel slip briefly and at random when starting a train. Here's an example video to illustrate what I mean: (https://www.youtube.com/watch?v=MQKbwiRZ7fY)
    It's kinda unrealistic to have them perfectly start every train they attempt ...
    As noted you have to use CAB (realistic) mode to see steam loco wheelslip. I'll note when it does occur in Trainz in my experience it is much less violent than the shown for the loco in your vid. But it does affect performance with loss of tractive force and visually with wheels rotating faster than normal.

    Wheelslip occurs when tractive force exceeds the friction force available at the wheel contact with the rail. Tractive force for steam locos is complicated and calculated in real time by the game engine but the steam-engine espec and drive bogey set most of the parameters used with the user setting cutoff and throttle. Adhesive weight is calculated in real time but is set totally by parameters specified in the loco config and the espec.

    The mass tag in the loco config sets most of the weight and should be the mass without water in the boiler. Effect of variable mass in other special queues like sand dome or the firebox are pretty much negligible. The boiler volume (for weight of water) is set by the espec, but lots - maybe most - of these are estimated values. You can use it to check on the total weight of the loco in operating condition. You might find the mass tag in the loco's config needs some adjustment.

    The driving-wheel-weight-ratio tag in the espec determines the "adhesive" weight supported by the drive wheels. It should be a realistic value for the loco - some aren't. Set primarily by the wheel arrg't and suspension characteristics, it can be estimated roughly if no data is available. I will say that it is much easier to adjust the weight ratio tag than to redo the steam container part of the espec as a fix for slipping problems.

    Tractive force for steam locos is determined by the game engine in real time using the parameters in the espec. Setting up a steam-engine espec, this is where the art really comes in. Driving them is kids play by comparison. With steam locos the applied force at the rail varies as the wheel rotates. Real ones have 2 max and 2 mins per drive wheel rotation. I'm not sure how accurately Trainz simulates this but it does vary as the drive wheel rotates. I see a lot of quarter wheelslip (partial anyhow) with the especs I make. While we like to think the locos' especs are developing realistic TE, it is an art creating good ones for Trainz.

    I don't think you can change the actual coefficient of friction the game uses, but you can change a few parameters that effect how slipping is treated after it starts. Parameters affecting actual % of tractive force losses when slipping occurs and the effects of sanding can be adjusted during game play using the Vehicle-Physics rule. They can also be changed with custom scripting.

    Also on articulated locomotives like the 4-6-6-4 Challenger and the 4-8-8-4 Big boy, it's possible for one set of wheels to have perfect traction while the other one is slipping, but that never seems to happen in this game.
    Yes definitely possible. The direct-drive tag in a bogey's config determines if it's linked to the steam physics used by the loco. When tag value = 1 (true) particle effects (smoke), sound and wheelslip are linked. When tag value = 0 (false) they are not linked. So if the front drive bogey is linked and the rear one is not you will see wheelslip only on the front set.

    For rigid frame duplex locos like the PRR T1, Q1 and Q2's slipping can also occur in either or both drive sets. PRR T1's had a reputation of slipping both when starting and at speed with either or both sets spinning. If the drive wheels are set up as 2 separate bogeys then it's handled the same as with articulated locos.

    [EDIT] Just to clarify Trainz doesn't consider the tractive forces or adhesive weight distributed between the 2 drive wheel sets. It's all on a per locomotive basis. When the TE developed exceeds the frictional force the wheels slip and tracitve force is reduced by the current values of the params controlling it. It makes no difference if 1 set, both or none show visual wheelslip. The effect on performance is the same. So in the articulated case proposed above when wheelslip starts the front wheel set shows visually slip, TE is reduced and the rear wheel set continues to rotate at the normal rate determined by locos current speed.

    Bob Pearson
    Last edited by RPearson; December 2nd, 2020 at 12:49 PM. Reason: just to clarify a point
    TRAINZ-UTC-TRS04-TRS06-TC1&2-TC3-TS09-TS10-TS12-TANE(TEG)-TMR17-TRS19
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