This is my attempt at explaining a design for a magmaless, pumpless freeze trap. Most traps of this type that I have seen on the wiki or forum use magma and a row of pumps. I have used this design successfully on a fort, and my brother has used it in one of his forts. In his case, the trap is built in a s-curve hallway to block archers, and is dubbed the "cold shoulder".
z+2 z+1 z0 z-1
_ . . . _ w . . . w w _ _ _ w
_ . . . _ w . . . w w _ _ _ w w w w w w
_ . _ f _ w . w . w w _ G _ w w H D _ w
_ . . . _ w . . . w w _ _ _ w w w w _ w
_ . . . _ w . . . w w _ _ _ w w w w _ w
_ . _ f _ w . w . w w _ G _ w w H D _ w w w w
_ . . . _ w . . . w w _ _ _ w w w w _ _ _ _ _
_ . . . _ w . . . w w _ _ _ w w w w _ w w w w
_ . _ f _ w . w . w w _ G _ w w H D _ w
_ . . . _ w . . . w w _ _ _ w w w w _ w
_ . . . _ w . . . w w _ _ _ w w w w _ w
_ . _ f _ w . w . w w _ G _ w w H D _ w
_ . . . _ w . . . w w _ _ _ w w w w w w
_ . . . _ w . . . w w _ _ _ w
w natural rock wall
f constructed floor
. open space
_ natural floor
G grate
H floor hatch (hooked up to drain lever)
D door (hooked up to flood lever)
Water is supplied from the right on z-1 from a reservoir. The reservoir is located higher than z0 to generate pressure. z+2 is the surface, and is above ground.
Upon pulling the flood lever, the doors on z-1 instantly open. Water pressure-teleports from the reservoir to the floor of z0 almost instantly, where it instantly freezes because it is exposed to the sky. The water does not freeze on the grates on z0, because of the hanging natural rock walls on z+1. This is therefore an 89% freeze trap and an 11% drowning trap.
The flood lever is pulled again to close the doors. The drain lever is then pulled to drop the water that is sitting on the grates and hatches to a drainage area. The drain lever is then pulled to close the hatches. The ice walls in the hallway can then be safely mined out. If a dwarven computer was used to replace most of the lever pulls, the trap could be fired and drained from one lever.
Advantages over other ice trap designs:
- Wagons can path through the z0 entrance hall
- Magma is not required
- Neither Pumps or mechanical power are required
- The design could be expanded to cover a larger area with ice, such as an entire courtyard:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ G _ _ G _ _ G _ _ G _ _ G _ _ G _
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ G _ _ G _ _ G _ _ G _ _ G _ _ G _
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ G _ _ G _ _ G _ _ G _ _ G _ _ G _ (the grates aren't necessary unless you expect wagons)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Disadvantages:
- The trap requires mining to reset
- The trap produces "water" stones
- The trap does not recycle water
- Unless you were able to ice them, flying titans/fbs could trash the device and enter your fort via the piping (this is also true for some other designs using pumps)
- Creatures that can't drown have a 1/9 chance of survival in this trap, on the grate tiles. You could mine a fortification in the ice and shoot them at your leisure.