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[smirk]

Kobolds. Kobolds are a problem. The trap-avoiding little bastards aren't good for anything but disrupting work orders and cutting up yer guard animals. And cleaning up clutter around your entrance only exposes dwarves to danger. So I set about inventing a needlessly complicated machine to solve this (not too complicated, actually). It's also pretty good at getting rid of sieges and goblin thieves, as far as my limited testing has gone. First pictures, and then explanation:

Spoiler: z+1 (click to show/hide)

Spoiler: z (click to show/hide)

Spoiler: z-a deep pit (click to show/hide)

EDIT: standard tileset pictures:

Spoiler: magma reservoir (click to show/hide)

Spoiler: main passage (click to show/hide)

Spoiler: pit (click to show/hide)

The fort entrance is on level z; ramps to the north lead outside, fort is off to the right. Z+1 is where the magma goes. Oh yes; like all good traps, there is magma. "But Smirk, you fool," I hear you say, "There's holes in that floor! Any magma you put in that room will drain out like yesterday's Taco Bell dinner!" Good catch, Hypothetical Reader, but those holes are in fact blocked. By the doors below them on level z. What this means is that as long as those doors are closed, the magma stays where it is. But as soon as one is opened, by, say, a kobold trying to steal your precious socks, magma floods down like the unquenchable wrath of Armok.

 Basically, what this does is exploit the AI's tendency to get into yer fort by the shortest route possible. Kobold and Goblin thieves can do this through locked doors, so all you need do is (l)ock those doors so your dwarves and any trade caravans will take the longer route to the left. Since doors claimed by invaders technically stand open, I've added an easily reclaimable door on the south end of the passage just in case all three magma doors get invaded (although I've not seen any invaders make it past door 2 before being swept away so far). Also, the grates next to the doors are necessary so that magma doesn't slosh out diagonally and block pathing.

Clutter: Just to the right of the magma doors is a pit that invaders are pushed into by the flow (stairway explained later). You can make it as deep as you like. The bottom isn't shown here, but I've grated it off with drainage so that any un-melted items can be recovered later. That's where this machine's other function comes in: the magma makes this an automatic de-clutterer, burning away invader remains and clothing and leaving nothing but goblinite.

Sieges: Now, sieges are a slightly different creature: To start with, they don't path through locked doors, so you'll hafta unlock 'em yourself and keep your dwarves away. Easy with burrows. Also, sieges have a bad habit of grouping around their dead leader and standing there looking ugly. For that reason, I've made the pit very deep and put a stairway in the center of it. What this should do (I'm pretty sure) is wash the lead invader into the deep pit, causing the troops to try and follow the body down to the bottom via the stairwell - triggering the trap in the process. Of course, I haven't tested it yet, so no guarantees.

Design Problems: It's a bit complicated to set up and you need a renewable magma source. Also, need to build everything out of magma-safe materials. The pit wouldn't be necessary, except in early designs un-meltable weapons blocked the doors open and led to an unstoppable magmafall. To help with this I built three hatches over the hole in the magma chamber and linked 'em to a lever so that the magma can be shut off in event of emergencies. The biggest problem, though, will probably be with building destroyers during sieges. I've only had 1 siege using this thing (the same siege where I figured out I needed to solve the leader problem), and luckily the trolls were stupid enough to stand right on top of the grate they were trying to destroy, so that goblins passing by and opening the first magma door also splashed magma diagonally onto the trolls and did away with 'em quite nicely. But I can't be sure that's repeatable behavior without more testing.

Speaking of testing, I'm gonna go do some more of that. Thoughts?


EDIT: Better/less confusing pictures.

[Bobnova]

I like it.
I will try this operation at the earlier opertunity.

[Noodz]

Brilliant. Never before have I seen such a simple yet elegant trap capable of dealing with lockpickers. It's like the bucket full of water on top of a door ajar prank, but with magma.

Though i do ask of you to post pics without any tilesets. Im used to playing matrix style and i cant figure out where the grates go

[Jacob/Lee]

I assume those red things with rows of dots on them are grates in picture 2. Might be wrong, though.

[smirk]

I assume those red things with rows of dots on them are grates in picture 2. Might be wrong, though.

Aye, that's them. Went ahead and put standard tileset pictures in the OP; should hopefully help.

No sieges yet. Gobbos are being coy.

[Viking]

This seems pretty promising Thanks for sharing this!

[lcy03406]

The biggest problem, though, will probably be with building destroyers during sieges

My idea is to build a shorter passage with the same design but replace the grade with a door(with ceiling). A building destroyer should pick the door path. - Does it follow the goblin leader? If it follows, it will always take a 'magma shower' triggered by its leader in your original design. If not, it can be separated by a shorter path.

[Trif]

Wow, that's a really neat trap! Massive kudos to you.

I have just one thing to add: excluding the trap area from the burrow won't prevent dwarfs from walking through there, they just won't accept jobs in this area. If you want to keep dwarfs out, use traffic areas.

[toomanysecrets]

I have just one thing to add: excluding the trap area from the burrow won't prevent dwarfs from walking through there, they just won't accept jobs in this area. If you want to keep dwarfs out, use traffic areas.

I've never had problems with dwarves leaving a burrow that is part of a military alert. And traffic designations do not prevent dwarves from going anywhere. They will even walk on restricted tiles if there is no other path.

[vjek]

Love the design.  Well thought out.

As a possible improvement, pressurizing the reservoir above would would likely make the response time faster, and then just expand the drain/sump to a fortification-map-edge for drainage. 
Dealing with the building destroyers will require some extra cleverness.

[Xenos]

Love the design.  Well thought out.

As a possible improvement, pressurizing the reservoir above would would likely make the response time faster, and then just expand the drain/sump to a fortification-map-edge for drainage. 
Dealing with the building destroyers will require some extra cleverness.

Or have a closed loop system that recycles your magma?  Give a floodgate/bridge linked resupply line to deal with evaporation but you don't need to worry much about the drain speed.

[NecroRebel]

With a design like this, it is completely impossible to have perfect magma recycling. When the intruders pass through the doors, magma will fall into the doors' tiles, and when the doors shut they'll atomsmash the magma that remains. Even under the best circumstances, you lose 1 unit of magma with every enemy that comes through, which will eventually drain any closed system. As such, you need a renewable magma supply, and if you want the thing totally automated, you would have to have it refilling automatically, too.

That's not to say that you can't recycle the magma - just make sure the pumps for the recycling system were build after the pumps that bring new magma in, and they'll work first - but you can't rely entirely on that.

As for the design itself, I've seen something similar before. The one I saw before had a 2-wide hallway that had magma-safe doors all along one side and magma all along the other, so enemies would consider the line of doors passable, but when they tried to go through them, like in your design, they'd get magma'd. Yours seems easier to repair if it's damaged or jammed, since it's easier to seal away the magma source, but also takes more space, so I don't think I can call it objectively better (though it's also not worse).

[Xenos]

With a design like this, it is completely impossible to have perfect magma recycling. When the intruders pass through the doors, magma will fall into the doors' tiles, and when the doors shut they'll atomsmash the magma that remains. Even under the best circumstances, you lose 1 unit of magma with every enemy that comes through, which will eventually drain any closed system. As such, you need a renewable magma supply, and if you want the thing totally automated, you would have to have it refilling automatically, too.

That's not to say that you can't recycle the magma - just make sure the pumps for the recycling system were build after the pumps that bring new magma in, and they'll work first - but you can't rely entirely on that.

As for the design itself, I've seen something similar before. The one I saw before had a 2-wide hallway that had magma-safe doors all along one side and magma all along the other, so enemies would consider the line of doors passable, but when they tried to go through them, like in your design, they'd get magma'd. Yours seems easier to repair if it's damaged or jammed, since it's easier to seal away the magma source, but also takes more space, so I don't think I can call it objectively better (though it's also not worse).

I was meaning a pump system to recycle magma that reaches the bottom of the pit to make draining a bit easier. if you are on a map that has magma a bit more difficult to acquire, or you recently flooded the world with magma and your volcano levels are a bit low.  Or you just want to collect that goblinite/koboldium ore more quickly.

[Panando]

That's very cool. I also note that the system could use water instead of magma, and flush enemies off a narrow walkway into a pit.

[Helgoland]

The leader would usually be flushed first, right? Then why not let the leader be flushed down a chute without a stair and provide an alternative way to the bottom chamber - lined with cage traps which will be triggered by goblins trying to reach the leader without all that "Oh my leader is caged I will not continue or flee" jazz. I'll have to try this out sometime - maybe someone else could redesign his system to try this?

Also, for building destroyers try a convoluted hallway that leads to a statue filled with traps (the hallway, not the statue). That should take care of them.