After watching the
degrinchinator I decided I wanted to make one for myself- only I wanted mine to be automatic, rather than having to mine out the ice every time.
Requirements:
- Freezing environment. (seasonal or otherwise, my proof of concept was on a glacier)
- Magma (finite, a magma pool is sufficient).
- Water (finite, melting ice is sufficient).
- Some wood. (for power to drive the pumps).
_No_ Magma safe materials required.
Side view:
Z +2 □□□□ □□□□
Z +1 □□□□M□□□□
Z 0 □□□□ >> □
Z -1 □□□□B<< □
Z -2 □ >> □□ □
Z -3 □ << □□□□
Z -4 □□□□M□□□□
Z -5 □□□□□□□□□
= Open space
□ = Wall / Unmined Rock
M = Pump Magma in here
B = Bridge (optional)
> = Pump ->
< = Pump <-
The upper pump loop should have water in it. A small amount of seed water (at least 2 deep) can be frozen and thawed repeatedly to fill it up. The system will tend to generate water while running, and may overflow a small amount.
The lower pump loop should have 3 deep magma in it. Ideally, this can be done by tapping into a magma pipe at Z-5 and pumping magma into the Z-4 Channel. This pump can be manually driven, as it should only need to be run once to fill it up, then left off.
The pumps should be attached to some form of power (perpetual waterwheels, or windmills) via a gear assembly that can be toggled on and off, one for each level.
Default state: All off. Oh look, A seige is coming! Wait until they pour onto the bridge, then flip the level for the Z-1 Pumps. In one frame, the water is pulled from the Z-2 reservoir and douses the seige, which is shortly frozen into a solid block of ice, killing whatever was inside and sealing the rest of the seige outside. You can then turn the Z-1 Pumps back off. Now to reset it without exposing your dwarves... Pull the levers for the magma pumps on Z-2 and Z-3, this will cause the magma to flow in a loop, warming the bridge and melting the ice. Pull the lever for the Z0 pumps to drain away the water. Then shut off the magma pumps to cool the bridge, ready for the next wave of attackers. Since we don't have to wait for the delay on any bridges, this can all be done quickly.
I've build a pressure plate sequence to automate this process (not currently shown). One throw of a level to turn the system on, and it automatically freezes and melts repeatedly until shut off.
The Bridge (optional) is intended for ease of cleanup- Once the seige is finished, drain the water back into its reservoir, then pull the lever for the bridge. All the bodies, clothing, debris, etc, will be dropped straight down into the magma, burning away all the crap. Just pull the lever for the Z-3 Pumps to hold the magma, leaving nice, neat piles of iron weapons and armor on Z-4. (If you don't want it incinerated, you can just pump the magma out first before toggling the bridge. The main point is to allow the trap to be reset and cleaned without ever exposing your dwarves to harm.) Unfortunately, freezing ice currently squeezes all other items in the tile into an alternate dimension.
As a result of the bugs, this is currently not a practical defense. When they get fixed, I'll write up a new, more detailed explanation, and probably make a movie/map of it to show it off. Until then, just send me a pm if you have any questions.
EDIT: Updated diagram to v1.1. Added note about pressure plate automation, and current bugs.