[scottb613]

Hi Folks,

RE: Steam Locomotives

Have there been any major changes to adhesion model in Open Rails lately ? I've been away for a bit but I now notice that steam locomotives seem to have their drivers rotate backwards on start up (slippage ?) - before changing directions to rotate the direction they should... This seems new to me...

In addition - I can't really get my drivers to truly slip anymore (I'm no expert) - I've tried decreasing the mass and increasing the power and nothing... From my limited experience watching some videos on YouTube - It seems that the engineer of large powerful steam locomotives is often fighting to keep slippage under control (example was an autumn run with possibly wet leaves on track)... It also seems that the sander in OR has little or no effect...

My recent upload to the ET library is the Heavy Mountain Bill Hobbs created the physics for... In MSTS - if I jam the throttle wide open - even on dry track - with a heavy load - the wheels slip... If I engage the sander - they stop... This behavior "seems" a little more realistic than what I am seeing in OR at the moment and I don't seem to be able to replicate this behavior in OR...

One other thing I've noticed - is that the train seems to have less power in OR... Do ENG files need to be tweaked to get matching performance in OR ???

If anyone cares to take a gander at my Mountain as an example - I would gladly accept any input given to see if the physics could be improved in OR... In order to help us novices - it might be beneficial if some of the subject matter experts took the time and show us how create an ENG file properly - using the new OR specific parameters - so we can attempt to replicate it on our own (maybe this has already been done and I just haven't seen it)...

As always - GREATLY appreciate all the work by the OR team and their contributors - I can still recall the very first release of OR and realize just how far we have come... Thank you one and all !!!

Regards,
Scott

[steamer_ctn]

scottb613, on 05 December 2014 - 05:43 AM, said:

Have there been any major changes to adhesion model in Open Rails lately ? I've been away for a bit but I now notice that steam locomotives seem to have their drivers rotate backwards on start up (slippage ?) - before changing directions to rotate the direction they should... This seems new to me...

In addition - I can't really get my drivers to truly slip anymore (I'm no expert) - I've tried decreasing the mass and increasing the power and nothing... From my limited experience watching some videos on YouTube - It seems that the engineer of large powerful steam locomotives is often fighting to keep slippage under control (example was an autumn run with possibly wet leaves on track)... It also seems that the sander in OR has little or no effect...

Based upon my understanding, the current adhesion model is not really designed for steam locomotive, but instead for diesels and electric locomotives. In steam locomotives, due to the crank positions the wheel forces, are not consistent for the full wheel rotation, whereas for diesels and electrics the forces are more even. The current adhesion model does not take into account these differences.

In regard to slip, my understanding is that under normal conditions (dry track), and if the factor of adhesion for the locomotive was high enough (>4), then it would be rare to experience slip on the locomotive. Certainly on wet track (or as you suggest with autumn leaves, etc) it was more likely that slippage would occur, but not guaranteed.

Currently there is a trial steam slip model in OR, but it is monitoring capability only, and does not impact the performance of the locomotive. It can be viewed in the extended steam HUD.

scottb613, on 05 December 2014 - 05:43 AM, said:

My recent upload to the ET library is the Heavy Mountain Bill Hobbs created the physics for... In MSTS - if I jam the throttle wide open - even on dry track - with a heavy load - the wheels slip... If I engage the sander - they stop... This behavior "seems" a little more realistic than what I am seeing in OR at the moment and I don't seem to be able to replicate this behavior in OR...

One comment, just because it happened in MSTS, doesn't make it correct. MSTS should NOT be used as the benchmark for performance accuracy, instead check against real locomotive performance.

As suggested above, on dry track with the correct FoA, it was probably unlikely to experience slip. On wet track, what you describe is probably realistic. The steam adhesion monitoring model should do as you suggest.

scottb613, on 05 December 2014 - 05:43 AM, said:

One other thing I've noticed - is that the train seems to have less power in OR... Do ENG files need to be tweaked to get matching performance in OR ???

The OR model should have the correct power based upon the key locomotive parameters, ie cylinder diameter, stroke, boiler pressure and drive wheel diameter. These parameters determined the tractive effort of the locomotive, ie the pulling power.

In MSTS, I think that the steam locomotive pulling power was set by the MaxPower and MaxForce statements, so if these have not been correctly calculated, then this may create errors in performance.

So to answer your question, OR should have the correct power (it might appear to be less then MSTS), and whilst the ENG files should be tweaked to suit some of the new OR parameters required to improve the accuracy of the locomotive specification, these tweaks will not necessarily increase the power capabilities of the locomotive, unless cylinder diameter, stroke, boiler pressure and drive wheel diameter are incorrectly set.

To "demonstrate" the accuracy of the OR physics model, I have created a test environment, with sample locomotives, and actual test reports done by the railways. Testing so far with these models suggests that the OR steam physics model is reasonably realistic. Try testing your locomotive in this environment against know operating conditions for the locomotive.

This test environment is very much a work in progress, so I am happy to have any support to improve upon it.

scottb613, on 05 December 2014 - 05:43 AM, said:

If anyone cares to take a gander at my Mountain as an example - I would gladly accept any input given to see if the physics could be improved in OR... In order to help us novices - it might be beneficial if some of the subject matter experts took the time and show us how create an ENG file properly - using the new OR specific parameters - so we can attempt to replicate it on our own (maybe this has already been done and I just haven't seen it)...

The information provided in the test environment is designed to try and help novices (and others) to understand the parameters that are of relevance in the OR steam model. And also to set expectations of locomotive performance to a "realistic" benchmark.

Over time, I would also like to see some prototype information to be made available on this page similar to the information provided for geared locomotives.

It should be noted that OR is continually developing so things are still changing, and hence some of the information may change or become outdated, so again it would be good for regular feedback or some content volunteers to assist in maintaining this asset.

Cheers

[copperpen]

steamer_ctn, on 05 December 2014 - 01:40 PM, said:

In regard to slip, my understanding is that under normal conditions (dry track), and if the factor of adhesion for the locomotive was high enough (>4), then it would be rare to experience slip on the locomotive. Certainly on wet track (or as you suggest with autumn leaves, etc) it was more likely that slippage would occur, but not guaranteed.

There have been a number of prototype locomotives that were well known for being "light on their feet" and prone to slipping, even on clean dry rail when starting. Even diesels and electrics have been known to slip heavily.

With the current state of OR advanced adhesion, I have mine set to Normal with up to 10% change and always get a wheelslip warning at the beginning of an activity, or after a restart of a saved game.

Steam drive wheels do slip in OR if the eng file parameters are not correct, IE: not enough weight and power too high, the 3DTS cab-forwards being a prime example.

[steamer_ctn]

For a quick high level look at Factor of Adhesion - see here.

As suggested it was a balance between putting as much weight on the drive wheels as possible without exceeding the load limits of the rails.

Another interesting aspect of railroading!!!

[scottb613]

Hi Folks,

Thanks for taking the time and WOW - that's some web site you put together... I'm going through it now and it will take some time to digest...

Looks like I have some work ahead of me...

Appreciate the help...
:thumbup3:

Regards,
Scott

[Coonskin]

I disagree with some of these comments. I'll look at them one at a time:

Quote

MSTS should NOT be used as the benchmark for performance accuracy...

Back when Bill Hobbs and myself were delving deeply into the way MSTS handled steam physics, we were both surprised at how close one could get to simulated performance using KNOWN values of prototype locomotives. Bill even developed a program in which prototype values could be entered, and the program would then calculate what values needed to be inserted into the MSTS eng file for the engine being replicated. Doing so resulted in the simulated model of an actual locomotive performing very closely to the known abilities of the prototype. Agreed: Not all MSTS eng files go to this extent and some are atrocious, but I feel it is a mistake to attribute such a bad performing eng file to a so-called "lack" of the MSTS steam physics abilities. OR will do well to even get CLOSE to what MSTS is capable of in the capable hands of a steam eng file guru.

Quote

...instead check against real locomotive performance.

That's all well and good IF one has access to an operable example of said engine. It is often rare for such basic things as tonnage ratings on a given grade to be known/published on an engine, more so the older the prototype engine was. Therefore, the calculating theory of the OR steam physics will need to be able to extrapolate from known data to produce an acceptably realistic result, such as was the case with MSTS.

An observation: Back in the mid-late 1980s I ran steam engines for a tourist operation. Once MSTS was available, I replicated that portion of line in MSTS, including very close gradients/profile. Using the eng values of which I refer, running the virtual versions were surprisingly similar to running the real deal.

The steam performance in OR has quite a ways to go yet.

[scottb613]

Hey Andre !!!
:thumbup3:

Hi Folks,

RE: https://www.youtube....h?v=mV0-2xvmguY

Again - I am a complete novice at locomotive physics and in awe of what I see around here...

On a whim though - thinking about all that was said here - I went to YouTube (it's a miserable cold rainy/slushy day in upstate NY) and searched for "Steam Locomotives in Action" - and the very first scene of the very first video listed - has a large steam locomotive slipping as it leaves a dry station on a clear day... I just think that slipping may have been more prevalent on large steam locomotives than some believe... My intent here is to just to pass along observations in the spirit of discussion to improve OR - as this as it seems an important factor in steam locomotive operation... I really appreciate all the feedback and advice !!!
:rotfl:

Regards,
Scott

[Coonskin]

Even on level track and dry rail, adhesion is a combination of many factors such as how much driver weight is on the drivers, how much HP the locomotive can generate at starting speed, how much weight is being started, etc.

Yes, a steam locomotive can slip on dry rail... even a light engine. I'm a bit embarrassed to share this incident, but I'll go ahead and do it to illustrate a point (even at my expense!) :thumbup3: ...

I had been running steam engines for ES&NA owner Bob Dortch for only a few months. I was young and beginning to feel that I was quite the Hoghead. We were switching our way around the train at the Eureka Springs depot and I was ready to back up light engine to the awaiting passenger cars. I was all reared back in the seat and had just brought the No. 1 (Baldwin 2-6-0 wood burner) to a stop after clearing the switch and was waiting for the ground crewman to line behind so we could back down and couple up. Owner Bob was down at the depot standing on the brick platform among the passengers and surveying his empire. The ground crewman gave me the "back 'er up" hand signal and I, using my foot, kicked off the independent brake. Imagine my surprise to hear and feel the No. 1 lose her footing and spin a few times! What I had failed to do was shut the throttle completely off when stopping, so therefore steam pressure had built inside the cylinders while the brakes held the drivers solid, not allowing them to turn. Thus, when I kicked off the independent brake, the steam pressure that had built up inside the cylinders immediately translated into released energy, which (of course) caused the drivers to slip. I'm sure Bob heard it and was wondering what in the world he had gotten into with that new Engineer he'd suckered into hiring! I never did that again and from that point on was much more attentive to my use of the throttle, Johnson Bar, brakes and such.

So, yes, typical steam engines can slip on dry rail... even a light engine when handled by an young and arrogant Engineer!!

[copperpen]

There was also a spreadsheet developed for UK steam locomotives that did the same as Bill Hobbs' one, input the known data and get the MSTS equivalent back, including the figures for the arcane Adheasion line.. I still have both archived on my storage drive.

[scottb613]

Hi Folks,

Would it be possible to modify either of these spreadsheets to output the required OR values as well ? I can work with spreadsheets but I haven't a clue on the equations or variables involved...

Regards,
Scott