Elvas Tower: Braking - Wheel Skid - Elvas Tower

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Braking - Wheel Skid Rate Topic: -----

#1 User is offline   steamer_ctn 

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Posted 20 April 2016 - 07:14 PM

Whilst developing the steam adhesion model, I started to reflect upon one of the other aspects of railway operation where adhesion comes into play, i.e. Braking.

During a braking operation if the wheel rotation is restricted sufficiently by the brake shoes (brake force) then it is possible for the wagon wheel to lose its 'grip' and skid on the rails. When a skid is induced the rails can be damaged, and the train can become a lot harder to manage and stop.

Is there an interest in this feature being added to OR?

If introduced it would only be a basic model first, and may not take into account any anti-skid devices on newer stock.

It may also uncover poorly defined wagon files with large values of MaxBrakeForce.

#2 User is offline   R H Steele 

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Posted 20 April 2016 - 07:38 PM

View Poststeamer_ctn, on 20 April 2016 - 07:14 PM, said:

It may also uncover poorly defined wagon files with large values of MaxBrakeForce.


It is always worthwhile to read what you're interested in, Peter. I really cannot comment on your idea - just don't know enough (yet).
But, I do have a question. In another thread, - that I cannot locate - there was a mention of the MaxBrakeForce value in wagons being too high in many cases.
What would be a range of values (ballpark figures / high to low ) that would work for wag files?

#3 User is offline   Genma Saotome 

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Posted 20 April 2016 - 07:58 PM

View Poststeamer_ctn, on 20 April 2016 - 07:14 PM, said:

Whilst developing the steam adhesion model, I started to reflect upon one of the other aspects of railway operation where adhesion comes into play, i.e. Braking.

During a braking operation if the wheel rotation is restricted sufficiently by the brake shoes (brake force) then it is possible for the wagon wheel to lose its 'grip' and skid on the rails. When a skid is induced the rails can be damaged, and the train can become a lot harder to manage and stop.

Is there an interest in this feature being added to OR?

If introduced it would only be a basic model first, and may not take into account any anti-skid devices on newer stock.

It may also uncover poorly defined wagon files with large values of MaxBrakeForce.


YES

To do a complete feature set will will require more than just skidding the wheels tho. AFAIK from reading mechanical drawings of the brake system as well as steam era literature MaxBreakForce() needs to be set in the range of 0.6 to 0.7 of the value of Mass() for the empty car. There are going to be a whole lot of .wags where that isn't the case and so adding the feature will probably require additio0n of an option to turn the feature off or on.

There is also the question of the empty/load brake, something that's pretty standard since the 1930's for cars that have a significant difference in Mass() when comparing the empty car to a loaded car -- cars like hoppers carrying coal or iron ore. The apparatus was simple: a lever positioned near the side sill at the trucks that would increase the brake force when the distance between the sill and truck frame was reduced (on account of a heavy lading) and return it to normal when the distance grew again after discharging the lading.

And so there will be a need to expand the parameter list for these cars to include a second "MaxBrakeForce()" as well as some value of Mass() to determine which of those two should be used.

It's not complex... just a bit more work to do it all.

FWIW skids produce a flat spot on wheels... they go whack whack WHACK! with every rotation.

#4 User is offline   keystoneaholic 

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Posted 21 April 2016 - 02:47 AM

If you really want to get fancy with this, if the season is set to Autumn for the activity and there are trees on the current tile then do we need to reduce friction to something like 25% of normal values to allow for the effects of wet leaves on the rail?

I'll just go and get my medication........

#5 User is offline   steamer_ctn 

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Posted 21 April 2016 - 03:19 AM

View PostR H Steele, on 20 April 2016 - 07:38 PM, said:

What would be a range of values (ballpark figures / high to low ) that would work for wag files?

Have a look at this calculator, as I built it based upon some of the suggested values from Westinghouse.

View PostGenma Saotome, on 20 April 2016 - 07:58 PM, said:

YES

I will create a blue print for it, and start working on it. (Update date - TBA)

View PostGenma Saotome, on 20 April 2016 - 07:58 PM, said:

To do a complete feature set will will require more than just skidding the wheels tho. AFAIK from reading mechanical drawings of the brake system as well as steam era literature MaxBreakForce() needs to be set in the range of 0.6 to 0.7 of the value of Mass() for the empty car. There are going to be a whole lot of .wags where that isn't the case and so adding the feature will probably require additio0n of an option to turn the feature off or on.

I have seen the following brake ratio figures quoted, and they are used in the calculator in the link above.

goods_br=0.68; // Brake ratio for goods
pass_br=0.82; // Brake ratio for pass
hand_br=0.2; // Brake ratio for handbrake
tender_br=0.82; // Brake ratio for tender
loco_br=0.75; // Brake ratio for locomotive

EDIT: I was contemplating linking it to the advanced adhesion model option. I am reluctant to add another "on/off" option as I think we have too many now as it is. This is probably another full thread worth of discussion.

View PostGenma Saotome, on 20 April 2016 - 07:58 PM, said:

There is also the question of the empty/load brake, something that's pretty standard since the 1930's for cars that have a significant difference in Mass() when comparing the empty car to a loaded car -- cars like hoppers carrying coal or iron ore. The apparatus was simple: a lever positioned near the side sill at the trucks that would increase the brake force when the distance between the sill and truck frame was reduced (on account of a heavy lading) and return it to normal when the distance grew again after discharging the lading.

And so there will be a need to expand the parameter list for these cars to include a second "MaxBrakeForce()" as well as some value of Mass() to determine which of those two should be used.

I agree that the variable mass of a vehicle needs to be looked at. Carlo and I have had some discussions about addressing it.


View Postkeystoneaholic, on 21 April 2016 - 02:47 AM, said:

If you really want to get fancy with this, if the season is set to Autumn for the activity and there are trees on the current tile then do we need to reduce friction to something like 25% of normal values to allow for the effects of wet leaves on the rail?

Interesting idea, but I think that the trees would have to be in close proximity to the tracks to be realistic. Having friction change if a tree is say 100m away from the track might be a bit of a stretch.

I have seen friction figures of down around 0.1 (10%) for leaves on the track, so it could be quite a slippery effect.


#6 User is offline   hroch 

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Posted 21 April 2016 - 03:40 AM

Hi.
Will you program friction between the brake shoe and wheels? And between brake linings and brake disc?

#7 User is offline   steved 

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Posted 21 April 2016 - 04:51 AM

So do we need to come up with a new .sms so we get the whack, whack, whack sound of the flat spots as they go by?
Oh and how about new track dynamics to account for the broken rail caused by severe flat spots.
The possibilities are endless. :lol2:

Steve

#8 User is offline   Hobo 

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Posted 21 April 2016 - 06:23 AM

Proper braking for the various types of wagons is definitely a good idea but please don't overkill the issue and make it unnecessarily complicated for the developers / programmers sake . I also agree with Peter about the ON/OFF switch . That is only used usually as a bypass if the operator has a problem with the function of the unit using that function . Well - if you have to bypass a function to run your train then what use is that function in the first place . You probably have to make changes to correct the quantities in Engine or Wagon file . The ON/OFF is usually the cop out .
Steve has stated that we all know and are aware of the many, many variants , but just keep it as simple as possible , yet functional without too many frills . It'll work just fine .
Just an opinion .

#9 User is offline   Genma Saotome 

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Posted 21 April 2016 - 07:49 AM

Pay no attention to the cynics, just do it. My hunch is it will have little obvious effect upon train performance when the data is right and a huge effect when the data is wrong. IOW it should act as a driver for people to fix their data, something that will have a very positive effect all over the place.

WRT values, all of the brake system mechanical drawings I have (many) from the New York Central (a very large American road) all say the same thing for boxcars and gondolas: 60% of empty weight. OTOH identical drawings from other railroads cite 70%. My hunch is everybody knew there was an ideal range of 60-70% and picked a number that "felt right" as it was impossible to know for sure. Given that the laws of physics are true everywhere it stands to reason that said guideline should apply to all freight cars.

WRT locomotives... I've seen the same value you cite.

#10 User is offline   Coolhand101 

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Posted 21 April 2016 - 10:58 AM

View Posthroch, on 21 April 2016 - 03:40 AM, said:

Hi.
Will you program friction between the brake shoe and wheels? And between brake linings and brake disc?


Cast-iron tread brakes are speed dependant with the same brake force. The lower the speed, the more risk of wheel slide.

View Postkeystoneaholic, on 21 April 2016 - 02:47 AM, said:

If you really want to get fancy with this, if the season is set to Autumn for the activity and there are trees on the current tile then do we need to reduce friction to something like 25% of normal values to allow for the effects of wet leaves on the rail?


I agree. Also this autumn theme was mention for MSTS but was never implemented.


Thanks

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