So I've been trying some trap designs to kill forgotten beasts, in a fortress with access to magma and water.
The plan was to lock them up in a hallway with bridges, flood it with magma and then add water. Kill any type of fb safely, leaving no poisonous excretions, poisonous blood or whatever. It works, but I'm looking to improve the design. What I have right now, sideways view:
__W__________W__ <- water chamber, floor is a retracting steel bridge, can be filled to 4/7 from reservoir
__W__________W__ <- magma chamber, floor is a retracting steel bridge, can be filled to 4/7 from reservoir
__W----------W__ <- floor covered with steel floor grates
__BD________DB__ <- killing zone: steel doors surrounded by raising bridgesAs soon as a forgotten beast turns up on any of the three cavern layers, I open another raising bridge that opens a path from its cavern layer into the fortress, leading through the killing zone. (It first leads through a hallway with engravings of all the forgotten beasts that died before in the fortress). As soon as the FB is in between the two steel doors, I lock both of them. Then I order the two raising bridges to the left and right of the doors to be closed, dump the magma, wait a moment to enjoy the sight of a burning FB if it is fleshy, then dump the water. They can't destroy the grates from below, because they can't path there.
They should be able to destroy the doors, but that takes long enough to have the bridges close first. Actually, for some reason no FB seems to be able to destroy the doors at all - I think this might be a bug in the most recent version of DF.
However, the problem is that cleaning up afterwards is time consuming. Digging out the obsidian from the killing zone is fast enough, but on the level above, the grates are choked, because the obsidian casting forms a floor there.
So I need to deconstruct the grates, channel out the floor and then rebuild the grates before the trap can be reused. A cumbersome step that I would like to skip.
Is there a way to make the trap more efficient? I have been thinking of making the hallway of death 2 z-levels high, but then a flying fb might survive?