Description
This is a test of a solution to the design problem posed by this post. Basically, we have a stacker with fewer open spots than the number of trains which may want to stop there. The goal is to prevent trains from leaving their origin stations until we know there will be open spots in the stacker.
I achieve this by having an unpathable station (named unreachable) which is normally disabled. Trains all have the following schedules:
iron_x(iron_1,iron_2,iron_3, etc. The iron ore pickup stations)unreachableiron_drop
If the stacker is empty, then, unreachable is disabled, so trains will skip it. If the stacker is partially full (which is detected using the rail signals in the stacker), then unreachable is enabled. This causes any trains still at iron_x to be unable to leave their station with a "No path" message. Once the stacker opens up, unreachable is disabled, so trains will skip it again.
One wrinkle is that multiple trains can leave their respective iron_x at the same time, overloading the stacker when they all arrive. The solution is to enable unreachable when the stacker is only partially full, so that if there are in-flight trains, they will still have somewhere to go.
Mods used
This blueprint uses the creative-fix mod for 0.16 to supply power and load and unload trains. All of the signalling is totally vanilla.