40d:Trap design

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This page is one of several inter-related articles on the broader topic of defending your fortress and your dwarves. This page will focus on the theory and design of complex traps, mechanical systems and other automation for defending your fortress, and also on unusual uses of simple mechanic's traps.

• Many defenses rely on complex traps as a central component, that are, essentially, the defense themselves. For designs that could be adapted to use any complex trap, see Defense design.

• See the Defense guide for a general overview of threats and considerations for fortress defense.

• For suggestions on disposing of nobles and other unwanted residents, see unfortunate accident.

• For a basic overview of how the different machine parts work and work together, see machinery.

• For suggestions on training, organizing and deploying soldiers and militia, see Military design.

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Editors & Contributors - Please see top of discussion page before posting.

Introduction

Simple one-tile traps* are just that - they exist only on their own tile, trigger themselves when a target walks onto that one tile, and affect only that one tile. Complex traps and automation rely on linking doors, hatches, floodgates, bridges and mechanic's traps to levers or pressure plates, along with machinery to provide the power to run some of the more diabolical designs. When the trigger is activated, it sends a signal to the linked device. That signal is not always as simple as "do it now", but it's specifically either to "open" or to "close". By manipulating what does what and when, and what follows from that, impressive results can be achieved.

(* specifically, the stone-fall trap, weapon trap, and cage trap.)

• To fully understand how these component objects work individually (before combining them into diabolical and complex combinations), see those main articles.

Trap strategies

These are some basic tricks that can be used with most any trap design, basic or complex.

Bait animals

Enemies will hunt down and kill friendly tame animals wandering outside if they have nothing better to do. Put a puppy on a chain in some random spot outside, build a few columns around it to reduce the chance of them shooting it, and trap that area to hell and back. Also known as the "Tar Baby" strategy.

Obstacle Course

Combining some intentional cave-ins, lots of cage traps, some weapon and stone fall traps, channels, and pressure plates is a sure-fire way to fend off an invading goblin army.

Circular path trap

Create a small area preferably 1 tile wide, and channel it out leaving one support under it. This MUST be connected to your base by a bridge so enemies will take it. Place a pressure plate at the end, linked to the support and another bridge into your fortress. line this area with weapon traps and line the exits of the subterranean area underneath this with cage traps. The area underneath must also lead to your base so the enemies will walk into the cages. then build another area just like this except have the entrance bridge be retracted/raised and have the first pressure plate link to it, so it is an endless game of cat and mouse (sort of)

Scattered traps

Another options for outside defenses is scattered traps. Most hostile forces will flee if they take enough casualties, and stone-fall traps can be quite damaging to goblins and are easy to set up. Cage traps work even on Bronze colossuses and Dragons. You just have to make sure your dwarves working outside actually stay near your traps - a fisherdwarf who goes wandering screens away from the nearest trap is not protected. A wall of traps is a passive threat to injure, kill or capture enemies who will happily walk right into them. (This can work so well that some players decline to use it, and prefer a more complex challenge.)

Protect your Mechanics & Haulers

Many basic traps will require some form of "maintenance" - either reloading or un-jamming, and haulers will often wander out to gather the loot from the deceased. Put the traps where those workers can be secure - either behind a dog-leg or L- or U- bend, or behind a raisable drawbridge. Another invisible ambush could be lurking just beyond the first (untriggered) traps - and somehow, usually is. Invaders with bows will turn unarmored haulers or a legendary mechanic into a pincushion, and tasks will be interrupted if your workers so much as have a line of sight to an unconscious goblin.

The enemy will take the shortest path

If the path where you will place your traps has bends, expect the enemy to take the most direct path - it's not guaranteed, but they will tend to hug the inside of a corner, and rarely detour to a dead-end (represented by "x").

      ╔═════════ 
  ║   ║xx    ??
  ║   ║x    ??? 
  ║???║   .????     ? = unpredictable path 
  ║???║  .╔═════
  ║ ??║ . ║         . = most likely path
  ║  .║☺  ║         ☺ = invader
  ║x  .  x║
  ║xx   xx║         x = unlikely detour 
  ╚═══════╝

Once in a straight hall, anything is possible (represented by "?"), but placing your best (or first) traps on the inside path near "inside" corners (and de-emphasizing outside "dead-end" corners) is the best bet. If two invaders are side-by-side, they will wander, and random actions are always possible, but if you had to guess, this is the way to do it.

Basic traps

These are the simple traps that are placed by a mechanic. They require one mechanism but do not require levers or triggers. They can be a quick, easy and brutally effective "first defense" for a fledgling fortress, but they can also be combined into key parts of more complex set ups.

Note that, in combat situations, mechanics (and others) have a nasty habit of wanting to clean or reload traps when they are triggered, regardless of who or what might be out there as well. Forbidding traps after they are built will keep Urist McGoblinBait from deciding to reload a stone trap in the middle of a siege. Just remember to unforbid them when things calm down, so the traps are all ready for next time. Or keep all traps unreachable with drawbridges or orders.

Simple traps will also be triggered if your own dwarves or pets fall unconscious on them. Something to consider when placing them in a potential combat zone.

Stone fall trap

This is the easiest trap to build, so you can easily build them in large numbers. Building lots of them is an easy way to earn experience for your mechanic, and add to the depth of your fort's defenses at the same time. Surround every intersection and stairway.

Weapon trap

The gold standard of lethal traps. This is the only simple trap that works repeatedly without reloading. They do get jammed, however. View the trap with the items in room t mode, and if there's a corpse inside the trap, it's jammed. None of the weapons on a jammed trap will function. It may be wiser to have several weapon traps with fewer weapons, rather than a smaller number of ten-weapon traps.

Using crossbows or other projectile weapons in weapon traps avoids the problem of jamming, but they must be kept loaded with ammo. Mechanics will load them with any ammo that is not forbidden. They will load each until each type of weapon has ten rounds of ammo. Hammers seem to jam less than swords or axes, and spears seem to jam the most. Your dwarves will attempt to unjam traps unless otherwise forbidden.

Cage trap

A very powerful type of trap. Maybe even too powerful - currently, even a wooden or glass cage can hold indefinitely any creature, even trolls and megabeasts. Also, a cage trap never fails. A large creature can shrug off damage from a stone or weapon trap, but nothing can escape from a cage. Use cage traps as your outermost traps to catch the occasional wandering animal, or angry wounded elephant or unicorn, or even zombies.

By placing a cage with a trapped animal and connecting it to a trigger, you can remotely release that animal. (Note - not all wild beasts will attack goblins.) This must be done after the cage trap has done its simple job of catching the creature, as a separate process.

Linked traps

These traps require a trigger such as a pressure plate or lever pull. They will require at least three mechanisms, one for the trigger and two to create the link. The trigger can be located any distance from the trap, typically close for a pressure plate or far away for a lever.

You can also 'Arm' a defense system that involves pressure plates by pulling levers 'Activating' said pressure plates. The process is also fairly simple and cheap. First, you need a lever that will activate the system, after that you need to channel out a section to put your pressure plates, this can be anywhere you would normally put a pressure plate, and be at least three blocks long (one for the pressure plate, two for ramps). Add the pressure plate in the middle of this channel and ramps on the far sides. Over this gap make a drawbridge that either retracts or raises to the left or right, and connect it to the lever made earlier. Connect the pressure plates to you Fun Creating System of choice, and voila, you have a working switch.

For a system that repeatedly activates automatically and regularly regardless of enemies, see Repeater.

Damage traps

These complex traps are designed to kill or maim.

Menacing Spikes

Menacing spikes or upright spears appear on the basic mechanic's Trap menu, but must be activated remotely to pop out of the ground and impale anyone standing on that tile. Vast forests of these can make any area a killing field.

They will not jam. They are very deadly to everything including your dwarves and animals. Steel ones are magma-proof.

Try planting a bunch of Upright Spear/Spikes in your main hallway, and link them all up to one lever. When invaders come near, give the order to pull the lever, but set it to Repeat. The lever will continuously be pulled and the spikes come up and down repeatedly, perforating most enemies in seconds. Making a grid and having them alternate is even more effective. Note that this takes a lot of time and mechanisms to build.

Dropping the Hammer

Lowering drawbridges on invaders will crush them into nothingness.

Try replacing the side wall of a part of your main entranceway with a drawbridge, big enough so it spans the whole hallway. To prevent enemies from wrecking it, you could dig a channel in front of it so its protected while its raised. Link the drawbridge up to a pressure plate or lever, whatever you prefer. Whenever you feel like it, activate the trap, and watch the drawbridge fall directly into the hall, utterly squashing nearly anything beneath it. This can be done with minimal effort and used to smash invaders, unwanted immigrants, nobles, or simply to destroy your garbage. This is based on the 'Dwarven Atom Smasher' device mentioned elsewhere in the wiki.

Note that sufficiently large creatures (those with a SIZE greater than 10) cannot be crushed - attempting to do so will instead merely destroy the drawbridge itself.

Intentional Cave-in

Supports can be linked to triggers. Building a section of floor that is deliberately held up only by a trapped support allows for an intentional cave-in.

• Invaders dropped into a pit can be wounded or killed. Or, in the case of a chasm, vanished entirely.
• Dropping a floor directly onto any creature will instantly kill it, regardless of its size.
• The cave-in will also knock nearby invaders unconscious. This will stun them, and also make them susceptible to simple traps (even if normally immune).
• Cave-ins will not reveal invisible invaders, such as ambushers (unless it kills them outright ^[Verify]).

The biggest drawback of this sort of trap is the "reload" process, which can be relatively time consuming. Have a drawbridge that can seal off the work area so your mechanics and masons can reconstruct the setup in peace.

Water traps

These traps drown or wash targets away. Carelessness can cause an entire fortress to flood and be lost. Use with caution.

Level 0

 ░░░░░░░░░░░░░░░░░░░░░░░░░░░░   ░  - Wall 
 ->++▼··················▼++->   -> - Direction of traffic
 ->++▼··················▼++->   ▼  - Down-Ramps (as visible from one level above = see ramp)
 ->++▼··················▼++->   +  - Floor  
 ░░░░░░░░░░░░░░░░░░░░░░░░░░░░   ·  - Open space 

Level -1

   ░░░░░░XX░░░░░░░░XX░░░░░░   X  - Inflow 
   ░░▲++▼··▼++++++▼··▼++▲░░   
   ░░▲++▼··▼++++++▼··▼++▲░░   ▲ - Up-Ramps 
   ░░▲++▼··▼++++++▼··▼++▲░░   
   ░░░░░░XX░░░░░░░░XX░░░░░░   ▼ - Down-Ramps

Level -2

   ░░░░░░xx░░░░░░░░xx░░░░░░   x - Outflow
   ░░░░░▲++▲░░░░░░▲++▲░░░░░
   ░░░░░▲++▲░░░░░░▲++▲░░░░░
   ░░░░░▲++▲░░░░░░▲++▲░░░░░
   ░░░░░░xx░░░░░░░░xx░░░░░░

If enemies are in the middle of Level -1, open the inflow, then the water will first trap, and then drown them. If the pit is full, close the in- and open the outflow. You can automate this by using pressure plates, or if you want to have more fun, replace the water with magma (which would require pressure plates and floodgates to be magma-safe).

Drown & Burn

A flooding room trap combined with an unextinguishable burning Lignite bin. The water will evaporate on the bin's tile, causing the water from the surrounding tiles to move to it, which then get evaporated as well. The water will also push the invaders onto the fire, causing them to burn to death... in a flooding chamber! Bwahahahaha

NOTE: Traps involving large quantities of water turning into steam are as effective at killing your framerate as they are at killing goblins. Use with caution, and have the cut-off lever at the ready.

Magma traps

These traps incinerate targets, or possibly encase them in obsidian. Magma does not play favorites - read up (again) on magma, and use with extreme caution.

Sealed Fate

Create an airlock using two bridges, two doors or whatever. Make it a medium-sized chamber, perhaps 10x10 or so. Channel out the floors around the rim, and rig up a system to pump magma into the room, or drop it from the roof. Enemies will quickly be destroyed, and with the magma in the channels, you can pump it out for future use or just leave it. The idea here is a re-usable magma trap; you can use this with a pressure plate, too. It also leaves behind any magma-proof items the invaders might have been carrying.

Magma Machicolation

Basically one (or several) very small (1 to 3 tiles), refillable reservoir(s) of magma on the upper levels of a wall, locked with (magmaproof) floodgates/grates/bridge(s). When gobbos gather under it, open the whole thing and the result should be something like this (in color):

= | = | = | = | = | = | =
. | 1 |!g!| 2 |!g!| 1 | 1
. | 1 | 1 |!g!| 1 |!g!| .
. | . | 1 |!g!|!g!| . | .

Like with other designs, you need infinite magma (in the long run) and get only the magmaproof loot, but at least it needs much less magma. This design is of limited use when on the ground level should be grass, since deadly bushfires can develop. But this effect could also be used for further damage done to your enemys, since really no AI will recognize the dangers of fire and happily walk through it.

Misty Surprise

In fact just a magma basin next to the path to your fortress, but with some constructions held by supports over it. To fire the trap, pull the lever attached to the latter, sit back and enjoy how the goblins ignite in the deadly magma mist (optional: laugh manically).

As usual you only get magmaproof loot, also the effect is unfortunately somewhat random, but at least you don´t need infinite magma for this design (IF you really use only constructions). The usual safety precautions concerning cave-ins, magma and magma mist apply.

Automation & misc trap designs

By clever and creative use of various elements, it is possible to create impressive automated systems that fill a variety of functions.

For a system that repeatedly activates automatically and regularly regardless of enemies, see Repeater.

See also computing for other, possibly related ideas.

Funnel trap

In any area you have observed animals to be common, create a large barrier in the shape of a cross - it can be a wall, a channel, slopes that have been removed, or a combination. Leave the very center tile of this cross open to traffic, and cover that central area with cage traps. If the wild creatures try to migrate across the map where you have constructed this, they run into the cross, and have a 50/50 chance to go around or through - if they go through, you've got them. The bigger the better.

It will also work against ambushes and sieges, with cage traps or lethal ones.

Chasm trap

The easiest chasm trap is just a retractable bridge, very high up or over a very deep hole; instead of flinging invaders when raised, it just drops them.

A more complicated collapsing spiral trap can take out ten goblins at a time. When finished, it looks like this:

          +++
..........+++
.++++++++#+++
.+╔══════.     # = retractable bridge 
.+║++++++.
.+║+╔══╗+.     + = floor
.+║+║A+║+.
.+║+╚═+║+.     . = open space
.+║++^+║+.
.+╚════╝+.     ^ = pressure plate
.++++++++.
..........     A = bait animal 

The goblins are lured in by a restrained bait animal, and can't shoot it due to the surrounding walls. Just before they reach the bait, they trigger a pressure plate that retracts the bridge and collapses the support holding up the whole spiral. Goblins, bait animal, walls and all plummet into the chasm.

When building, you will need to build a span of floor underneath, for the support, as bridges do not support constructions (which is also why you want a bridge as the access, so it will not hold up the trap*). You will also need to have a floor tile between your floor and solid ground or wall while constructing, as the bridge alone will not work as a base, but you can remove it once the support is in place.

(* A set of floor bars or grate would work as well, but the bridge can aid in the (re-)construction of the trap.)

Land Mines

In any suitable open area which hasn't been dug out underneath, build a support and an adjacent multi-use pressure plate set to trigger on creatures (but not citizens), link them together, then build floor tiles above the support and pressure plate. When an enemy steps on the pressure plate, the game will pause and recenter the view with the announcement "A section of the cavern has collapsed!", at which point the enemy will be crushed and its companions will be stunned or knocked unconscious by the cloud of dust (though not necessarily revealed, in the case of an ambush). As added bonuses, by using a multi-use pressure plate, the collapsing floor will deconstruct the plate and usually leave its mechanisms lying on the ground for reuse, along with other building materials used (the materials used to construct the support and floor tiles, plus the mechanism used in the support) - alternatively, if a single-use pressure plate is used, both of its mechanisms (but not the one used in the support) will be destroyed, making this one way to dispose of low-quality mechanisms created by unskilled engineers (aside from selling them to caravans, dumping them in magma, or crushing them under a drawbridge).

Bridge Land Mines

Although this takes quite a few mechanisms and a lot of carpenters to pull off, you might be able to create a minefield on a bridge. Create a very long moat and a bridge crossing it. Make sure this bridge is not your outermost bridge. This bridge should be at least 20 squares long, but make sure it is no more than 4 squares wide. Then set up a ton of pressure plates in a checkered pattern, build a floor above the bridge, and make supports next to the pressure plates. Then remove the floor tiles not on the supports, destroy the up-stairs on to the floor, and link all your pressure plates to a support. As soon as a goblin walks on them, the floor caves in and makes an explosion knocking him and the friends he has near him off the bridge drowning them.

This should not be used as the only defense. Make sure you have other traps at the ready in case of large sieges.

NOTE: This is a very expensive creation and should only be used late in the game when you can spare lots of stone/wood/mechanisms. The bigger the bridge the more effective the trap.

Retract bridge 2 to force invaders to take the long way, first running along the wall (to the west in this diagram) and then zig-zagging back for maximum exposure to your ranged units on the walls above them. The pits at the base of the walls are necessary to target down one z-level at enemy units.

(Note - Traders will NOT stop at your fortress unless there is a clear, 3-wide path to a Trade depot when they arrive. Bridge 2 should be kept down if you want/expect Traders.)

Bridges 1 and 3 can be put down to allow enemies into this pit entrance, then retracted again to trap them in the kill zone. Note - Attackers must have a complete "path" to where they want to go, so bridge 3 must be down to lure them in.

Pitfall Trap

A simpler type of Bridge Landmine, related to the above Chasm Trap. Construct a number of retracting bridges over a pit, leaving one empty square over which you should construct a floor tile. Put a pressure plate on said tile, and link it to all the bridges. What you do with the pit is limited only by your imagination and your interest in recovering enemy weapons, armour and cave spider silk underwear.

Variation A: A long retracting bridge in the entrance tunnel, with the pressure plate right in front of the fortress doors. The expression on the face of the point-goblin who reaches them only to watch his comrades plunge to whatever gruesome fate you have prepared for them will be a mental picture to cherish.

Variation B: Much as above, but outside and with a raising bridge.

Degrinchinator

Observe: http://mkv25.net/dfma/movie-231-degrinchinator

Twin Paths

Vexed by how to safely collect loot and clean traps when ambushes are always ready to spring? Don't want to sacrifice animals? This trap is like the above-mentioned chasm trap with one difference: When the bridges are retracted, anything on them falls into a pathway the same shape as the bridge pathway. This pathway contains many (or ideally is covered by) weapon traps. A lever attached to all the bridges can spring or reset this trap, and a pressure plate part of the way down the bridge path can catch ambushes. This method drops invaders or ambushers to where your dwarves can safely loot them, and if one of your own dwarves is caught, the weapon traps do not target them.

Semi-automatic Orcsicle maker

Similar to the afore mentioned Degrinchinator design but with the possibility for corridors 2 tiles or more wide and without the need to mine the ice out again afterwards as it all melts at the push of a lever and is drained away with pumps.

Observe: http://mkv25.net/dfma/movie-1675-semi-automaticorcsiclemaker

Basically you heat a corridor from below with magma. You can then flood this corridor with water without the water freezing (because of the magma). Then if you remove the magma from the room bellow the water will freeze killing anything in it. Refilling the room bellow with magma melts the ice allowing pumps to drain the room.

In depth design, pictures and caveats for this trap.