Loco Steam Brakes

Loco Steam Brakes

Postby SteveP_trains » Tue Jun 06, 2017 5:08 pm

Hi All
I am in the process of constructing a few of the Ffestiniog locos & coaching stock for Steve Fleming's (ThePhantomPhish) Ffestiniog route that some of you maybe aware of.
I am having a problem getting the locos to work with both Vaccuum Brakes and Steam brakes in the engine blueprints.

Train Braking using vacuum systems is not a problem and works fine. However, the Loco Brake (using Steam Brake definitions) simply don't want to respond.

Interestingly, I have not found any steam locos that use this combination that work either - the settings are all there in the blueprints but I find that switching to Loco Brakes has no effect whatsoever and you can drive away as if no braking was being applied.

Wondered if any of you have managed to get this to work successfully or have any ideas??

Cheers

Steve
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Re: Loco Steam Brakes

Postby VictoryWorks » Wed Jun 07, 2017 9:42 am

Ed is the expert on these things so hopefully be can offer you some advice but based on his previous advice to me I think the solution is to use a loco air brake and script it so it pretends to be a steam brake.
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Re: Loco Steam Brakes

Postby DominusEdwardius » Wed Jun 07, 2017 10:33 pm

There's no real quick and easy way of doing loco brakes, what Pete says is correct using a loco air brake to act as steam brake is pretty much the only way of doing so (Loco only Air brake with air single pipe).

However this creates an unfortunate issue, when running with vacuum brakes, due to a game bug the loco air brake will drag every time the train vacuum brake is released! This is due to a bug which says the brake cylinder pressure for the loco brake is the vacuum brake pipe pressure in psi (so 10.3psi brake application when the vacuum brakes are released). Strangely it would appear from memory that it causes both the train and loco brake to drag hence you get an issue like on the B1 where the drag is quite enormous.

The work around is two fold, firstly setting the maximum brake cylinder pressures to be something very high (say 300+psi) (not forgetting to change the main reservoir and compressor values to match!). This has the effect of negating the drag of the brake before. Previously if the max pressure was say 50psi, with the 10psi bug the loco brake would be applied 20% with the vacuum brake released. With the max pressure at 300psi the brake is applied 3.3% and hence the drag is massively reduced.

Since on most locos, the steam brake is technically independent of the vacuum brake (being applied by a pressure difference usually) it is usually possible to run the locomotive with the vacuum destroyed and using the independent steam brake handle to control the brakes. In the current situation this creates issues however since currently when you'd apply the vacuum brake, the train brake would come on full force stopping the locomotive dead. The work around is to make the vacuum brake effectively do nothing on the locomotive, this involves setting the train brake % to a low percentage, preferably 0% but unfortunately this causes issues with the dispatcher since the things the loco doesn't have brakes. As such the lowest you can go is setting the brake force % to be about 5-10% for the train brake percentage to keep the dispatcher happy. This also has the added benefit of reducing drag from memory but excuse me if it doesn't as I've not had to work on this stage for years ;)

This does however now mean the vacuum brake does nothing to slow the locomotive, and hence lua scripting for the locomotive is needed to set the locomotive brake to the desired application based on what the vacuum brake is doing. But this is probably a bit beyond this post.

regards
Edward
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Re: Loco Steam Brakes

Postby SteveP_trains » Fri Jun 09, 2017 9:04 pm

Many thanks Edward for that very detailed response. I think I have followed it :D
I will take a look in detail once I have finished the model as I am not sure it will be worth the effort involved at this stage.
If nothing else, it was good to understand that the problem is a bug and not something I missed.

Cheers
Steve
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