Elvas Tower: OR Roller Bearing Friction at Low Speed, 0-5 MPH Range - Elvas Tower

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OR Roller Bearing Friction at Low Speed, 0-5 MPH Range What is the equation OR uses to calculate this? Rate Topic: -----

#21 User is offline   steved 

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Posted 29 January 2020 - 08:12 AM

What's that old saying?
A steam locomotive can start a train it cannot pull, a diesel locomotive can pull a train it cannot start.
Or something along those lines.

Steve


#22 User is offline   scottb613 

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Posted 29 January 2020 - 08:37 AM

View Poststeved, on 29 January 2020 - 08:12 AM, said:

What's that old saying?
A steam locomotive can start a train it cannot pull, a diesel locomotive can pull a train it cannot start.
Or something along those lines.

Steve


Hi Steve,

Nice !!! New one on me...
:)

Regards,
Scott

#23 User is offline   wacampbell 

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Posted 29 January 2020 - 09:13 AM

View Poststeved, on 29 January 2020 - 08:12 AM, said:

What's that old saying?
A steam locomotive can start a train it cannot pull, a diesel locomotive can pull a train it cannot start.
Or something along those lines.

Steve

I think you have that backwards.

#24 User is offline   steved 

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Posted 29 January 2020 - 09:36 AM

View Postwacampbell, on 29 January 2020 - 09:13 AM, said:

I think you have that backwards.


Could be. Wouldn't be the first time.
I heard it a long time ago.
Google is our friend.. http://www.railway-t...-vs-diesel.html

Steve


#25 User is offline   steamer_ctn 

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Posted 29 January 2020 - 07:30 PM

Hi Scott,

View Postscottb613, on 29 January 2020 - 07:19 AM, said:

I came across Part 2 (just realized each volume is made up of monthly periodicals):

Thanks for that.

View Postscottb613, on 29 January 2020 - 08:01 AM, said:

It mentions the actual starting "Starting Friction" of train IS NOT the controlling factor of how much tonnage a locomotive can move - - - while "Starting Friction" IS most definitely the controlling factor in ORTS as it stands today...

Can you share the real life scenario that you are trying to replicate with OR, and why you believe that the starting friction in ORTS is the controlling factor is this scenario?

#26 User is offline   Lamplighter 

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Posted 30 January 2020 - 01:27 AM

View Poststeved, on 29 January 2020 - 08:12 AM, said:

What's that old saying?
A steam locomotive can start a train it cannot pull, a diesel locomotive can pull a train it cannot start.


I agree, technically it corresponds to:
For this reason, steam traction had to use a rack on slopingly demanding lines.
Diesel cars and locomotives can handle such a track adhesively.

#27 User is offline   scottb613 

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Posted 30 January 2020 - 05:15 AM

View Poststeamer_ctn, on 29 January 2020 - 07:30 PM, said:

Hi Scott,

Thanks for that.


Can you share the real life scenario that you are trying to replicate with OR, and why you believe that the starting friction in ORTS is the controlling factor is this scenario?


Morn'n Peter,

Thanks for the interest...

Sure - there is no real life scenario I'm trying to replicate - my comment was simply relaying information that I've noticed during countless hours spent on literally thousands of test runs with a constant scenario - while modeling various steam locomotives and freight cars - in hopes of improving our physics... Your fantastic site hosting a wealth of information is what enables me to do this...

I think most who gravitate here are relatively serious physics aficionados - as for me - that's the difference between a sim and a game... I guess that's why I find myself pouring over century old tomes written by men who are no longer living - about machines that no longer rule the rails - trying to glean some new information... I don't have an engineering degree - I don't pretend that I have one on TV - and - I didn't even stay at a Holiday Inn Express last night - - - so this is all from a layman's perspective... The realistic physics we enjoy is what keeps me solidly entrenched with ORTS - as the other products I've tried seem to pale in comparison in this regard...

Regarding my statement :

Quote

It mentions the actual "Starting Friction" of train IS NOT the controlling factor of how much tonnage a locomotive can move - - - while "Starting Friction" IS most definitely the controlling factor in ORTS as it stands today...


It seems obvious given the information we've previously discussed and what we see in the sim - that since we don't have draft gear slack modeled properly - ORTS totals the friction for the entire train vs car by car on startup - and that at zero speed friction is greatest - that my statement seems undisputed... In my humble opinion - starting a train realistically would be of far greater importance than processing the few pounds of wind resistance change as a train passes through a tunnel (which we do have)... I think we can agree - the more realistic we can practically make the physics - the better...

Like others mentioned here - I've noticed that starting resistance seems very high and have thought similar to these folks countless times... To bring this to my current project - a USRA Mikado - I can't get more that 25 loaded USRA boxes started on a 0.5% grade - yet it will happily pull 30 or more up the same grade if I start on level track and have the train moving at slow speed when I encounter the grade... For a Mikado - without access to any performance reports - that sure seems like a pretty short train to be unable to move... In all my testing - I've never seen a point where I have the train moving and it stalls out in the 5 to 10 MPH range because the load is too great - if I can get it started - I can pull it - given a constant grade... This result contradicts the information presented in the linked articles...

Since we don't always have available test data for our subjects - I try to find similar data as a basis and use that to form my opinions - such as the following... I also use anecdotal evidence such as photographs that mention the number of cars being pulled - etc etc etc - and weigh that in for consideration...


Quote

How Many Cars Could A Locomotive Pull ?

The gauge of pulling power of a locomotive was its tractive effort rating, but this was the horizontal pull only when starting. As speed increased less average tractive effort was possible. This was due partially to friction but chiefly to the fact that the boiler could only produce a certain amount of steam per minute. Modern engines where faster than older ones, with a given load, because they had bigger boilers, more heating surface, feedwater heaters, and other devices to produce a greater flow of steam.

Another thing that limited pull was that the friction of each car in the train increased with speed. A typical loaded freight car might weigh 70 tons. To start it moving, the engine had to exert a force of 220 lbs. But if speed increased to 50 miles per hour, the engine had to pull more than twice as hard - 470 lbs - to keep the car moving. An empty car only required 150 lbs to get it started and 300 lbs to keep it moving at 50 miles per hour.

The following table shows the relative pulling power of three types of freight locomotives at three speeds. It is assumed that all cars weighed 70 tons loaded and that the road had a 0.3 percent grade. The three engines were: a Reading 2-8-0 Class L9sb, a Frisco copy of the USRA Heavy 2-8-2 equipped with a Coffin Feedwater Heater and a Front End Throttle, and finally a Lehigh Valley 4-8-4 Class T1 with Elesco Heater and Front End Throttle.

Loco____Start Force___Start_______25 MPH____50 MPH
===============================================
2-8-0____64,400 lbs____93 Cars____39 Cars____13 Cars
2-8-2____66,700 lbs____94 Cars____63 Cars____22 Cars
4-8-4____66,400 lbs____95 Cars____69 Cars____27 Cars

If the cars were empties, about half again as many could have been pulled.

***This information is based on data in the July 1932 issue of Baldwin Locomotive Magazine.



============================================================================================================================================
If a heavy 2-8-2 can start a (94) car train on a 0.3% grade - it seems as if a light 2-8-2 should be able to do a little better than (25) cars on a 0.5% grade (my test cars are only 62 tons)...
============================================================================================================================================

And there's those pesky Feedwater Heaters again...
:)

It also specifically mentions it takes 220 lbs of force to start a 70 ton car moving on Friction Bearings... That's a massive difference from what we see in ORTS...

Given this data - I guess I could create a new ENG file based on a USRA Heavy - use a 0.3% grade - increase the weight of my boxes to 70 tons - then see if our results are similar ? I'm pretty doubtful - even my Heavy Mountain (on rollers) and Heavy Consolidation which have greater tractive effort can't start more than 45 or so... There are only (4) ORTS Parameters that should affect power produced in a steam locomotive (sans slipping) that I can think of (Boiler Pressure, Driver Diameter, Cylinder Size, Cylinder Efficiency)...


So - a little about my testing scenario - I always use the same setup introducing as few new variables as possible during test runs... This also allows me to gauge relative performance between various locomotives... All my testing has been done with steam... I have two - well really three "paths" I use for every test...
  • Starts on a 0.5% Up grade
  • Starts on level track and increments up in steps Up from 0.3% - 0.5% - 1.0% grades - with long enough runs at each to determine if the train will stall on the specific grade...
  • Starts on a 0.3% Down grade and runs form several miles Down various 0.3% - 0.5% - 1.0% grades


1 and 2 are used to test the pulling capacity and 3 is used for testing brakes...

I add and remove my "standard" loaded USRA Box for testing different car numbers and weights...

I know you've mentioned your reluctance to make any changes to the physics unless hard data can be found supporting that change and that's great to a point - if the information doesn't exist or not accessible - someone took a swag at this initially and it's possible they were just plain wrong - perhaps we should consider an intelligent approach to improving this best guess scenario when we lack data ?

Again - I am immensely grateful for all you have done and continue to do - my intent here was simply to relay helpful information to hopefully improve what we have - please feel free too use or discard as you see fit...

Regards,
Scott

#28 User is offline   steamer_ctn 

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Posted 30 January 2020 - 10:48 PM

View Postscottb613, on 30 January 2020 - 05:15 AM, said:

The realistic physics we enjoy is what keeps me solidly entrenched with ORTS - as the other products I've tried seem to pale in comparison in this regard...
Then this makes it even more important to ground OR in accurate real life performance information.


View Postscottb613, on 30 January 2020 - 05:15 AM, said:

Like others mentioned here - I've noticed that starting resistance seems very high and have thought similar to these folks countless times...
This may appear to be the case because the slack coupling may not be working as efficiently in OR at this time, as in real life. Just because OR may not handle slack coupling well at the moment, doesn't necessarily mean that the starting resistance values that it uses are unrealistic.

Even on a real train it may be difficult when starting on a gradient to "bunch" the train up, and therefore it may not be possible to take advantage of slack in this scenario. Hence even real trains may have difficulty starting on a gradient. Sometimes trains that have stalled on gradients must be halved to get them to the top.


View Postscottb613, on 30 January 2020 - 05:15 AM, said:

It also specifically mentions it takes 220 lbs of force to start a 70 ton car moving on Friction Bearings... That's a massive difference from what we see in ORTS...

My concern with using anecdotal data is that it may give a false impression, especially as it doesn't have sufficient supporting information.

For example, a starting resistance of 220lb for a 70ton car implies a value of approx 3lb/ton. This value is very light and is even lower then the minimum values offered by AREMA, which are 25lb/ton for sliding bearings, or 5lb/ton. So given the age of the stock in the information source, were they sliding or roller bearings?
Are you able to provide the original article in the July 1932 issue of Baldwin Locomotive Magazine.


View Postscottb613, on 30 January 2020 - 05:15 AM, said:

I know you've mentioned your reluctance to make any changes to the physics unless hard data can be found supporting that change and that's great to a point - if the information doesn't exist or not accessible - someone took a swag at this initially and it's possible they were just plain wrong - perhaps we should consider an intelligent approach to improving this best guess scenario when we lack data ?
The somebody who took a swag at it initially was me so it was based upon information that I found during research on the topic, and I am always open to reviewing code, and changing it where we can demonstrate that it is not performing against a real world yardstick.

However if we proceed to make changes based purely upon personal perceptions rather then real life information, then we risk damaging the thing that attracts you to OR, ie the accuracy of the physics.

As I have stated previously on a number of occasions I am open to working with a small team to set up a testing scenario to review the performance and if necessary make changes to the code based upon these test results. For reference I am currently undertaking a similar exercise with diesel locomotives.

If you would like to do a similar exercise for steam locomotives, then I would be happy to work with you on this. It would require you to set up some test stock (based upon my choice of stock), do some research, and undertake testing. Let me know if you are interested.

#29 User is offline   scottb613 

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Posted 31 January 2020 - 09:25 AM

View Poststeamer_ctn, on 30 January 2020 - 10:48 PM, said:


Are you able to provide the original article in the July 1932 issue of Baldwin Locomotive Magazine.



Hi Peter,

I had looked previously - they have one on eBay @ $49.00 USD or so - while very pricey I'd be willing to pick it up if I knew it was the Holy Grail we needed - my fear - is it would just reiterate what I already posted or not have it at all... They have the table of contents listed but I don't see anything that looks like this article... I've had that quote for years and honestly I forget where I picked it up...

I think I'm interested enough to attempt to replicate the Heavy Mikado test myself - I might try to knock it out over the weekend - I'll post the results if I do...

https://www.ebay.com...4.c100667.m2042

Thanks for the offer - I'll consider it and let you know... It would be nice to make this a real "team approach" perhaps including some other subject matter experts as well (few and far between - I know) ?

Regards,
Scott

#30 User is offline   scottb613 

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Posted 31 January 2020 - 11:05 AM

Hi Peter,

Sorry - one more question - did anything it that article I linked standout as new data that might prove beneficial to our cause ?

Thanks...

Regards,
Scott

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