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Variable Mass() Rate Topic: -----

#1 User is offline   Genma Saotome 

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Posted 01 March 2016 - 04:37 PM

Is there anything in OR that addresses a value of Mass() that varies within the activity? Examples are consumption of fuel by diesel locomotives, consumption of fuel and water in steam locomotive tenders, refueling of those just mentioned, and possibly open top cars when they take on or dump their loads (e.g., coal).

The question came to mind when I was reviewing some locomotive specifications and saw an 8t difference between unfueled and fully fueled... and the .eng file specification was in the middle.

Varying weight will have an effect upon both braking and friction; The locomotive I was reviewing was almost always used in sets of 4 units, often 5 or 6 and so the combined extent of potential variation could be as much as 48t. I would expect that number would be greater on modern locomotives as they are so much heavier. The difference between empty and fully loaded open tops cars is often 4-5X the weight of an empty car.

#2 User is offline   Csantucci 

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Posted 02 March 2016 - 12:35 AM

View PostGenma Saotome, on 01 March 2016 - 04:37 PM, said:

Is there anything in OR that addresses a value of Mass() that varies within the activity? Examples are consumption of fuel by diesel locomotives, consumption of fuel and water in steam locomotive tenders, refueling of those just mentioned, and possibly open top cars when they take on or dump their loads (e.g., coal).

The question came to mind when I was reviewing some locomotive specifications and saw an 8t difference between unfueled and fully fueled... and the .eng file specification was in the middle.

Varying weight will have an effect upon both braking and friction; The locomotive I was reviewing was almost always used in sets of 4 units, often 5 or 6 and so the combined extent of potential variation could be as much as 48t. I would expect that number would be greater on modern locomotives as they are so much heavier. The difference between empty and fully loaded open tops cars is often 4-5X the weight of an empty car.

At least for the cars provided with the OR-specific freight animations (continuous type) the mass is variable and depends on the amount of freight load.

#3 User is offline   Hamza97 

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Posted 02 March 2016 - 12:50 AM

I always set the .eng file parameters for for fully fueled locomotive. OR then reduces the weight of locomotive as the fuel gets used up. Just tomorrow I completed a 150 km run with a diesel locomotive (18 passenger coaches - 868t total train weight, 110kmph max permitted speed, FYI). The locomotive was fully fueled (6000 litres) and weighed 126 tons, by the time I finished the run it was 125.5 tons. So that locomotive was lighter by 0.5 tons. Don't know if that's correct.... :)

#4 User is offline   Coonskin 

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Posted 02 March 2016 - 05:14 AM

FWIW:

Real world experience w/US railroading: And an engine with a large (3000 US gal.) tank that's full will hold the rail better than one tha's near empty.

#5 User is offline   Lindsayts 

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Posted 02 March 2016 - 06:22 AM

View PostCoonskin, on 02 March 2016 - 05:14 AM, said:

FWIW:

Real world experience w/US railroading: And an engine with a large (3000 US gal.) tank that's full will hold the rail better than one tha's near empty.


3000 US gal of diesel would weigh aprox 21,000 lbs around 9700Kg.

Lindsay

#6 User is offline   sim-al2 

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Posted 02 March 2016 - 07:39 AM

The ability to specify passenger weight would be nice too. Many commuter and subway vehicles have load compensation valves that react to vehicle load, and vary braking and propulsion levels proportionally. However, older vehicles didn't, and heavy loads required the driver to compensate properly.

Freight cars are rather interesting in this regard too. European railways had freight cars as early as the 1920's with manually-set brake proportion levers (Empty/Load Lever) under the car, usually with 2 or 3 positions that were to be set depending on the car's load, to ensure that loaded cars could be run with reasonable braking performance without risking skidding on the empty cars. In modern cars, these manual valves are often replaced with automatic proportioning valves, which offer continuous adjustment of braking power. Similar valves are also found in modern North American cars, especially cars with fairly large differences between empty and loaded weight, such as coal gondolas.

#7 User is offline   Genma Saotome 

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Posted 02 March 2016 - 09:17 AM

Interesting. So OR does change the weight in some situations.... The values of these parameters are all influenced by the value of Mass():

  • Friction()
  • MaxBrakeForce()
  • DerailRailForce()
  • DerailBufferForce()
  • actual adhesion


Do they also change as the weight changes?

#8 User is offline   Csantucci 

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Posted 02 March 2016 - 12:32 PM

Friction is recalculated at every program loop and has the mass as one of its parameters. Therefore friction dynamically depends from mass (at least for OR-specific freight animations).

#9 User is offline   steamer_ctn 

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Posted 02 March 2016 - 01:34 PM

View PostCsantucci, on 02 March 2016 - 12:32 PM, said:

Friction is recalculated at every program loop and has the mass as one of its parameters. Therefore friction dynamically depends from mass (at least for OR-specific freight animations).

Does the freight animations use the main FrictionForceN calculations in the MSTSWagon file?

If so, friction relies on the Davies co-efficients multiplied by the speed of the train. The Davis co-efficients are calculated externally to OR, and they do take into account the mass of the wagon (but only a full or empty wagon scenario). Therefore, for the main friction calculations (and possibly freight animations), variable weight is not considered at this time, but is fixed at the value of the Davies co-efficients in the WAG file.

To adjust the friction values for a wagon with a changing mass, the full suite of Davies formulas would need to be incorporated (and this wouldn't allow for some freelancing by modellers with different Davies co-efficients) into OR, with a means to differentiate between the different wagon types.

Alternatively, perhaps the full and empty Davis co-efficients could be included in the WAG file, and a sliding calculation done between these two limits to adjust the friction with a changing mass.

#10 User is offline   Csantucci 

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Posted 02 March 2016 - 01:44 PM

Peter, if I look at the Update method within MSTSWagon.cs I see that MassKG is used many times within the code part that computes friction, and MassKG is modified few lines below accordingly to the percentage of load.

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