NumWheels ()

[meeshu]

What exactly does this parameter/statement mean and do?

Based on some searches here, and according the plainsman (Bob Bouduin), this statement is supposedly not the number of wheels and not even the number of axles on locomotives and cars.

So what is the the purpose of this NumWheels () statement, and how are values within the brackets/braces determined?

[pwillard]

Its related to "axle count". With regards to OPEN RAILS, it isn't very sensible. It remains for MSTS compatibility.

This value is no longer required and has been superceded by the sum of ORTSNumberAxles and ORTSNumberDriveAxle.

[R. Steele]

The quote below was a response by steamer_ctn to my question about the "NumWheels" parameter. This post and others can be found at Elvas Tower when searching the forum for "NumWheels" --- I suspect you will probably find some information here also.

Please see steamer_ctn's very excellent website -- especially the section on physics >>> https://www.coalstonewcastle.com.au/physics/

Hi Gerry,
Thanks for the encouragement.

For once this is a case where the "documentation" leads the code changes.

I recently came across the full Davis article, and some articles by Davis predecessors, which he used in developing his now famous formulas. In particular these articles that described a potential model for starting resistance which was better then the original model that I incorporated into OR. So I am in the process of updating it based upon the information described on the resistance page as part of the work that I am doing on Advanced Couplers. At the moment it has not been added yet, but hopefully within the next week it will be added to the Unstable version.

The NumWheels value is incorporated in two locations in the ENG file. The first one in the wagon section of the file, and represents the non-driven wheels on the wagon. The other value in the engine section represents the driven wheels on the locomotive.

This value is taken as the number of axles (I know that the name doesn't seem to line up, but it has been preserved as a legacy MSTS condition).

I suspect that in MSTS it was used as a "fudge" factor, so hence there maybe some unusual values in older files.

I will advise when the starting resistance changes are made to OR.

[R. Steele]

This value is no longer required and has been superceded by the sum of ORTSNumberAxles and ORTSNumberDriveAxle.

True -- but only if the user is conversant with and using OR physics....otherwise OR code is probably trying to decipher all sorts of weird and inaccurate numwheels parameters in old msts files.

meeshu -- are you using ORTS physics parameters or running default msts eng and wag files?

[meeshu]

Thanks for the comments.

Running default MSTS locomotives and rail cars. So there are no ORTS . . . statements present within the respective *.eng and *.wag files.

The quoted link seems to contradict what plainsman said in a number of posts. In that plainsman said the NumWheels() was not directly equal to the number of wheels nor axles on all rail equipment.

[derekmorton]

There is a problem looming here.

Derail code is using numwheels and not the ORTS parameters.

---------------------------------------------------------------------------------------------------------------------------------------------
// Train will derail if lateral forces on the train exceed the vertical forces holding the train on the railway track.
// Coupler force is calculated at the rear of each car, so calculation values may need to be from the car ahead.
// Typically the train is most at risk when travelling around a curve.

// Calculate the vertical force on the wheel of the car, to determine whether wagon derails or not
// To calculate vertical force on outer wheel = (WagMass / NumWheels) * gravity + WagMass / NumAxles * ( (Speed^2 / CurveRadius) - (gravity * superelevation angle)) * (height * track width)

[baldwin]

As far as I am aware, ORTSNumberAxles and ORTSNumberDriveAxle are used in eng files in conjunction with total weight and weight on drive axles to determine adhesion characteristics.

[pwillard]

This is why I feel the current DOC set for Open Rails is incomplete.

[derekmorton]

As far as I am aware, ORTSNumberAxles and ORTSNumberDriveAxle are used in eng files in conjunction with total weight and weight on drive axles to determine adhesion characteristics.

It is, BUT Numwheels is being used in the derail code.

[pschlik]

Per the code, NumWheels() and ORTSNumberAxles() in a wagon file behave nearly identically. The only distinction between those two is that a NumWheels() value of 6 or higher is ignored and 4 axles is used instead (I believe the assumption is that someone entering NumWheels ( 8 ) has probably made the mistake of entering the number of wheels when that's meant to be a number of axles...though an 8 axle wagon can exist). NumWheels ( 4 ) and ORTSNumberAxles ( 4 ) produce identical results-a wagon that's simulated as if it has 4 axles (if you define both in the same file, it seems that it's preferred to use the ORTS entry rather than the MSTS one).

Now despite the similar behavior, it is better to use ORTSNumberAxles() since that is less confusing and that supports things with 6 or more axles.

[meeshu]

In an earlier post by plainsman (a vey knowledgeable physics guy) some years back he states -

RE: NumWheels value in the .wag file

. . . . The numwheels value is NOT related to number of wheels or axles on any type of object. . . .

So, once again, how does one determine the correct values to enter for NumWheels if there is no relation to actual number of wheels and/or axles on railroad equipment?

This is for cases where the *.eng and *.wag files do NOT have similar ORTS . . statements within the respective *.eng and *.wag files.

[derekmorton]

That was written for MSTS not OR.

[pwillard]

Considering that Open Rails does try to fix things that were wrong or lazy implementations with the original SIM, some statements once held as 'gospel' have become deprecated.

Even fixing spelling errors like the word "adhesion".