Dodgy physics

[MikeK]

I have been having troubles taking long (120 - 150 car) stack trains down the steep south track on Cajon pass with only dynamic brakes. It seems that shortly after the rear of the train gets onto the 3% grade, the train derails and using the "8" key quickly I can see the cars go flying half a mile into the air. If I use only train brakes this doesn't happen.

The tonight I saw something weird also involving stack cars that I am hoping someone can duplicate. This is using the dash-9 pack from steam. Can someone try this?

- Go into the free roam scenario called "[DASH 9] Free roam: Dash 9s at Victorville"
- On the east side of the main lines are a pair of heritage 2 dash 9s, a line of coal cars, and a line of woodchip hoppers.
- Grab the dash 9s and move them to the track with the coal cars. I eased up to the coal cars at 1 mph and hit them with no throttle or brake.
- Here is where the "awesome" physics engine kicks in: as soon as I couple to the coal cars my speed instantly accelerates (with no throttle). Shouldn't the line of cars stop my locos? How could motionless cars make my locos accelerate?
- When the coal cars hit the end of the track they derail. When this happens quickly hit the "8" view and look around ...
- The line of stack cars on the other side of the main lines has flown 200 feet into the air for absolutely no reason!

I tried this 5 times in a row and got the same result every time. Can anyone else try this for me to see if there is just something wrong with my installation?

Much appreciated!

[TrainMaster1]

This is pretty close to what would happen in the real world....what you need to do is set a minimum reduction on your air brakes in conjunction with the dynamics. The dynamics only work on the locos and in most sims only the lead unit.

Think of it this way....you are slow down the engines but all that weight behind is free wheeling....never a good thing. Also are you talking 120-150 tables? On BNSF this train of your size would exceed TOB ratings and immediately draw a speed restriction. BY rule you cannot exceed 6500 tons or 8500 feet on track 3.
This train has a 10mph restriction as described.

So set a minimum air application and leave it on until you hit the bottom of the grade...do not release it. You can then adjust the DB as you need to but on that grade they would be screaming. That is why most heavy train use 1 and 2 downgrade to avoid this very situation with weight, length and speed restrictions.

The physics sound fine the train is too long and heavy and is not close to prototype is the real culprit.

Nick

[Kali]

- Here is where the "awesome" physics engine kicks in: as soon as I couple to the coal cars my speed instantly accelerates (with no throttle). Shouldn't the line of cars stop my locos? How could motionless cars make my locos accelerate?

Yeah, that one shows up in all sorts of places; the default UK HAAs do the same thing ( also when you stop the train and let the brakes off again ). I'm not sure if it's just brake setup, or brake setup and strange couplers. There is a lot of wierdness in the physics engine though.

[MikeK]

Also are you talking 120-150 tables? On BNSF this train of your size would exceed TOB ratings and immediately draw a speed restriction. BY rule you cannot exceed 6500 tons or 8500 feet on track 3.

This train has a 10mph restriction as described.

That is interesting, I didn't realize those limitations existed, thanks!

That doesn't explain why a derailment results in half the train being hundreds feet above ground level though :)

[arizonachris]

Mike, have you cleared the blueprint cache (tools and docs tab on the RW launch screen) I've made it a habit every time before I click "Start". You can get some really weird stuff happen otherwise.

[Importz2k1]

Mike, I had the same problem, what fixed it for me was a complete re-install of the game and assests. Took me all day as I did not use the package manager. I installed my assests manually one by one. I have noticed considerable faster loading times also this way rather than having everything on the package manager.
I've also noticed the by doing this, everytime I verify the cache my assest do not dissapear.

[MikeK]

Thanks for the replies, I will try clearing the blueprint cache then completely re-installing if that doesn't work.

[Toripony]

Now if only we could set that "minimum" train brake like in the real world. But all the locos put 15-20 lbs of pressure on as soon as the valve is cracked open. This is wrong. An engineer should be able to setup 2-20 lbs as desired. I used to be able to "trick" the brakes into letting me set low pressures like 3, 6 or 10 lbs but the new TS locos are even worse than the RW2 ones and I can't even trick them. Big peeve of mine. Am re-adjusting the brakes on all my locos to be like real life.

[Kali]

Tori/others, can you either give a quick explanation/drop me a link to how US automatic brake controllers are set up? UK brake controllers ( when they're not EP like most new ones ) - all two different types! - have a minimum application which off the top of my head is 15PSI under maximum, then a range of fully adjustable pressure ( Graduated Self-Lap in RW terms ) and then Full Service, which is maximum cylinder pressure. UK ( and european ) rollingstock can also partially release and reapply brakes at any time, unlike US stock, so I'm imagining US engines have a very different brake configuration.

Maybe taking a look at the cars might help with the surging issue also. I've done a fair bit of messing with european stock, not at all with US yet.

[MikeK]

Tori/others, can you either give a quick explanation/drop me a link to how US automatic brake controllers are set up?

Here is a long but interesting read that I found with a quick search: http://www.railway-technical.com/brake2.shtml

It really emphasizes how much work the RW will need to do to get the US braking systems right.

[Kali]

Yeah, really need how the controllers are set up; the principle of automatic airbrakes is common to every system, but the values & setup isn't by any means.

[Toripony]

It's not my area of expertise but there folks here who know the settings and engineers who know how it should work. What I have done is speak to 3 real-world engineers (who play train sims) to confirm my observation of trains and operating rules here on the Alleghany mountain. Trains here typically ran with a light "running brake" pressure on the train to keep the tail from pushing the front. Also, passenger trains in day of old did this to lessen the shock of speed changes to the passenger coaches. I was recently told by an engineer:

"Oh yes, 5-7 psi is the normal setting for service stretch braking. 10psi and above in passenger service for stopping at stations. I have noticed in RS, that when you do this , the train slows very rapidly, which is incorrect. You should be able to overpwer the brakes, and drag them along. This is common practice in the winter, to warm and clear the brakes, prior to stopping.

One other thing. I see no way to "Bail" the independent brake. The Independent brake on the locomotive sets up, when train line, or "service" is applied. On the type of brake they use in the bottom display, it would be a ring you would oull up. In the SD-40, it would be by pushing the independent lever downward... Just some thoughts."

And I have this from the C&O and Chessie rule books (they did this in the steamer days, too):

"EB limit is 35 mph from Alleghany to Clifton Forge. Trains over 100 cars must set and maintain 6 lbs train brake from Alleghany until consist is yarded at Clifton Forge. Trains over 140 cars are limited to 30 mph."

Another engineer said to me once, "I would never move a long train without some brake on it. It's about controlling the train; I don't like the train shoving me around and controlling me".

Personally, in RW and TS I don't feel in control of long trains of 80 to 100 or more cars without 3-4 lbs of brake on the cars. On the new SD40-2, F7, Genesis it is now impossible to set this light "running brake".

[Toripony]

More quotes from an engineer:

"You question would fill books...and it has! The method you are refering to is called "service stretch braking", using a minimum of 5-7 psi and stretching the slack out and lightly power braking the train never to exceed above notch five. It is common, but you cannot do it for extended periods, since your whole trains brake shoes would overheat. Then there is "power braking, which is 10-15 psi, slack stretched out, and using the throttle, never to exceend above notch six...and is used while stopping at stations. There is the "slack bunched method with dynamic brakes and train service brakes..and many more.. The key to train handling, is "knowing the road".. You must know how your train will handle, such as you many be puling with the head end, but your tail is still coming down a grade, a mile back. It is all very interesting, but is covered in volumes of publications. I was lucky, and was taught by some "old heads" I suggest, if you are interested in this kind of stuff, to do an Amazon book search for "Track and Train Dynamics", a very useful publication. Also, google transalert.com or The Railway Education Bureau. Look for the books, "The Elements of Train Dispatching" Vol 1 and 2. They both have very useful information within, and help greating....even in a simulator. Finally, check out Al Krug's site "Tales from the Krug". He is a friend, and a retired railroad engineer, who has wrote some of the stuff for these books. I hope this helps!

http://krugtales.50megs.com/rrpictale/rrpictale.htm"

(Note: on the EB Alleghany grade, they weren't concerned about brake shoes, they worried about a 12,000,000 lb 140 car runaway train running into the mills and factories of Covington or the service shops at Clifton Forge.)

[Kali]

"Oh yes, 5-7 psi is the normal setting for service stretch braking. 10psi and above in passenger service for stopping at stations. I have noticed in RS, that when you do this , the train slows very rapidly, which is incorrect. You should be able to overpwer the brakes, and drag them along. This is common practice in the winter, to warm and clear the brakes, prior to stopping.

One other thing. I see no way to "Bail" the independent brake. The Independent brake on the locomotive sets up, when train line, or "service" is applied. On the type of brake they use in the bottom display, it would be a ring you would oull up. In the SD-40, it would be by pushing the independent lever downward... Just some thoughts."

Ok, I had a huge post all ready to go and then FF crashed, so hopefully I remember it all...

Point 1: it might be that the stock just has too much brakeforce. I found a document somewhere with some tests for US stock braking - of course I have lost it since - and it was frighteningly low by european standards, I think somewhere around 25-30% of vehicle weight if I remember right ( and was reading it right ). It might be good to know what those guys think about overall brakeforce/stopping also. There are other possibilities like pressure mismatches making some stock brakes come on a lot harder than they should.

Point 2: First off, do the engine brakes come on automatically when you use the automatic brake? in UK stock which is what RW appears to model behaviour on, the straight air ( engine ) brake is controlled by the auto brake in the distributors, so you can't take it off without taking the auto brake off. Given once upon a time freight trains here had varying amounts of the train braked, that's probably not a bad idea. So... as it stands, bail-off isn't possible.

However I did have an idea to try; need to try making the engine's train brake airpiped - which means it won't do anything on the engine and then hook the engine-only brake up via the engine script if it does actually come on with the auto brake. That way you can still independently control the engine's brakes, which leads me to ask how exactly do you bail them off anyway? what's the procedure/knobs/buttons/etc? making the engine's train brake airpiped might stop it being able to apply the auto brake at all, but it's worth trying to bend the rules there just in case that one slips by because they never thought anyone would try it! :)

WRT to general brake function I guess the fastest thing to do would be to find a driver's manual. Quite easy to get here, someone's collected a lot on one website... anyone got an old Geep manual or something knocking around?

The culprit for the SD40 minimum application at least is this line in the simulation file:

Code: Select all

                                       <MinimumReductionPressure d:type="sFloat32" d:alt_encoding="0000000000001840" d:precision="string">6.0000</MinimumReductionPressure>


in the TrainBrake section. Change that to 0 and you should have full control.

Incidentally I've been messing with some heavy trains on BoQ, which has quite some hills at times... and I've also noticed the couple-get shoved backwards at 12mph issue which does seem worse than RW2.

[MikeK]

how exactly do you bail them off anyway? what's the procedure/knobs/buttons/etc?

I believe the handle for the loco brake goes left and right to apply or release the brakes, and can be pushed downwards to bail them off.

Incidentally I've been messing with some heavy trains on BoQ, which has quite some hills at times... and I've also noticed the couple-get shoved backwards at 12mph issue which does seem worse than RW2.

I am glad it is not just me. I hope someone from RW sees this thread!

Tory, interesting read. I remember seeing an article in Trains Magazine a while ago about distributed power. They mentioned that the section of track between Truckee and Reno on the Donner pass route has a stepped profile, so engineers with distributed power would put the locos on the rear of the train into throttle position 2, and use dynamic braking for the locos at the front of the train to control the speed. That way the cars stayed bunched up as the train went over the varying grades.