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[Marrik]

hey, i want to make it so that just inside the entrance to my fort is a pit of spikes or magma or some such, with a retractable bridge over it, so that any attacking enemies can be dumped into said pit. are there instructions anywhere for how to do this

[Tevish Szat]

okay, first pick your site: it needs to be 10x10 or smaller.   Then, channel out the area that the bridge is going to cover.  Continue to channel as deep as you want/dare.  You'll probably need access shafts, but can wall these off later.  Fill the bottom of your pit as you choose: spikes are the easiest: build the trap component menacing spike at a valid workshop (glass furnace, forge, or carpenter's shop: metal from the forge is deadliest), and when you have some b-T-S to build upright spears/spikes on the bottom of your pit.  10 spears/spikes per tile is deadliest, but especially for coverage on a big bridge, you can go with as few as one.  If you want to be assured of kills, attack the spike patches to a single lever (b-T-l to create a lever, new job > link to Spears/spikes from the lever to attach): you can pull this lever on repeat to perforate any goblin that happens to survive the fall.  Not necessary, especially if the fall is long (10+z) and the pit inescapable.

The bridge itself is constructed by b-g.  Use umkh to resize it to cover the whole top of the pit and make sure it is listed as "retracts" (s when placing, but it's the default state).  It takes architecture and one other labor (probably masonry if you use stone) to construct.  Attach it to a lever, preferably one in a high traffic area of your fort for quick response time: again, b-T-l to make a lever, then a new task from the lever to link it to the bridge.  Creating a lever takes 1 mechanism (from a mechanic's workshop) while linking to an object takes 2, so to get a proper retracting bridge you need 3 mechanisms.

That's the basic setup to create a drop-'em-to-their-deaths trap.  you can get more diabolical, like having magma at the bottom, or very clever about the placement, but ultimately  what you need to do is channel out the pit, fill the bottom with something deadly if you don't trust the fall to do the job (and I don't: a 13z pit scheme regularly left survivors for me until I installed spikes), and build and connect the bridge.  anything else is gravy.

[Naresomez]

Keep in mind that if there are too many gobbos/ heavy creatures, the bridge may not retract, so if you're not confident in you military, have a secondary trap line (though some frown on this, saying it prevents "fun").

[Sphalerite]

Keep in mind that if there are too many gobbos/ heavy creatures, the bridge may not retract, so if you're not confident in you military, have a secondary trap line (though some frown on this, saying it prevents "fun").

True, although the limit is based on the heaviest single creature, not the cumulative weight.  A hundred goblins on a bridge won't prevent it from retracting, but a single elephant, rutherer, or draltha will.

[Marrik]

maybe i should have 2 bridges that are both built to a central support, and both retract when the same lever is pulled? is that possible?

my idea was to have a narrow bridge across a huge chasm, with narrow fortified walkways only accessible from the far side around both edges of the room, allowing crossbowmen to shoot at whatever is on the bridge if 1 or both fail to retract

[Sphalerite]

It is certainly possible to link one lever to two bridges.  There's no easy way to have one lever pull retract one bridge and extend the other, but if you want both bridges to retract or extend at the same time you just need to build the lever and then link it to both.

[Naresomez]

If you only wanted the one lever for both bridges, one would have to be up, and one would have to be down (a functional "airlock" system), which is pretty easy to do.
Link the first bridge to a lever, pull the lever (thus bridge retracts), then link the second bridge. Though, if you run into the weight problem, and the bridge stays down while the other extends, you'll have to rebuild one of the bridges to get back to the up/down system.

[Triaxx2]

Alternately, you can carve your pit with up/down stairs, stopping one level above where you want to stop. Run a line a few spaces, and channel at the end. Then move back one space and channel out, erasing all but the last ramp. Now channel down. When you get the end of the pit build a bridge from the stairs to the ramp. Make it a retractable bridge, and use a lever to retract it. Now they can't get out and you can drop them enmasse. If you want you can even use pillars to support long bridges and spike traps at the top to knock off anyone that gets trapped up there.

[Sphalerite]

If you only wanted the one lever for both bridges, one would have to be up, and one would have to be down (a functional "airlock" system), which is pretty easy to do.
Link the first bridge to a lever, pull the lever (thus bridge retracts), then link the second bridge. Though, if you run into the weight problem, and the bridge stays down while the other extends, you'll have to rebuild one of the bridges to get back to the up/down system.

This absolutely does not work.  Levers don't send toggle commands, they send 'open' and 'close' commands.  The bridges will both synchronize to the same state after the second lever pull.

[nutzy]

I'm not sure if this is what Naresomez was trying to suggest, but you can use a lever to toggle bridges; it's a little hacky and exploits the 100 step lag between a lever pull and a bridge raising/lowering, though.

If you pull a lever twice very quickly (less than 100 steps) a bridge will toggle because of lag. If the bridge is up and the first pull tells it to raise, it won't do anything until the second pull lowers it. On the other hand, if the bridge is down the first pull will raise it and the second pull will be ignored because it is in the process of raising.

Just queue two pulls every time you use the lever and you will always toggle all of your bridges linked to that lever unless some dwarf wanders off after the first pull or some large creature stops a bridge from raising/lowering. You might want a lever for each bridge individually in case they get out of sync. If you do that you won't have to rebuild a bridge to fix your airlock.

I've never relied on this because it seems like too much of an exploit, but it works pretty reliably.

[Tibbz2]

okay, first pick your site: it needs to be 10x10 or smaller.   Then, channel out the area that the bridge is going to cover.  Continue to channel as deep as you want/dare.  You'll probably need access shafts, but can wall these off later.  Fill the bottom of your pit as you choose: spikes are the easiest: build the trap component menacing spike at a valid workshop (glass furnace, forge, or carpenter's shop: metal from the forge is deadliest), and when you have some b-T-S to build upright spears/spikes on the bottom of your pit.  10 spears/spikes per tile is deadliest, but especially for coverage on a big bridge, you can go with as few as one.  If you want to be assured of kills, attack the spike patches to a single lever (b-T-l to create a lever, new job > link to Spears/spikes from the lever to attach): you can pull this lever on repeat to perforate any goblin that happens to survive the fall.  Not necessary, especially if the fall is long (10+z) and the pit inescapable.

The bridge itself is constructed by b-g.  Use umkh to resize it to cover the whole top of the pit and make sure it is listed as "retracts" (s when placing, but it's the default state).  It takes architecture and one other labor (probably masonry if you use stone) to construct.  Attach it to a lever, preferably one in a high traffic area of your fort for quick response time: again, b-T-l to make a lever, then a new task from the lever to link it to the bridge.  Creating a lever takes 1 mechanism (from a mechanic's workshop) while linking to an object takes 2, so to get a proper retracting bridge you need 3 mechanisms.

That's the basic setup to create a drop-'em-to-their-deaths trap.  you can get more diabolical, like having magma at the bottom, or very clever about the placement, but ultimately  what you need to do is channel out the pit, fill the bottom with something deadly if you don't trust the fall to do the job (and I don't: a 13z pit scheme regularly left survivors for me until I installed spikes), and build and connect the bridge.  anything else is gravy.

Just wondering... What a retracting bridge?

[gtmattz]

A retracting bridge is a bridge that does not raise into a 1 tile wide 'wall', but instead disappears.  It is built with teh same commands as a raising bridge,  but you simply do not assign a raising direction (b-g, set size and position, done).  Please refer to the wiki page regarding bridges for a more thorough explanation.

[Triaxx2]

Point of interest, my pillar suggestion does have two further advantages.

1) The pillars can be set up to collapse with use of a support, somewhere down the height of the pillar. This makes it possible to drop them if something too heavy steps on them. (Sorry Mr. Too-Heavy for the bridge Titan.)

2) The pillars can be rebuilt and thus reused.

[Tibbz2]

A retracting bridge is a bridge that does not raise into a 1 tile wide 'wall', but instead disappears.  It is built with teh same commands as a raising bridge,  but you simply do not assign a raising direction (b-g, set size and position, done).  Please refer to the wiki page regarding bridges for a more thorough explanation.

Haha, sorry, but i meant to say 'Why' a retracting bridge

But thanks, that sort of answers it anyway xD

[khearn]

Be aware that the timing of a lever pull can be very uncertain. Plus, there is a 100 tick delay between the lever pull and the bridge retracting. So trying to get a dwarf to pull the lever 100 ticks before the goblins will be on the bridge is pretty difficult. Chances are that either the bridge will retract before the goblins get to it, or (far more likely) all the dwarfs will be busy gathering socks and the only dwarf available to pull the lever will be a long ways away, resulting in a bunch of goblins getting across the bridge before it retracts. Better plan a backup system for that case, because it *will* happen. Probably more often than not.

A better way would be to have a pressure plate at the end of the bridge, with a hatch right after it.

Code: [Select]

side view:
___========^h___
XXX        X XXX
XXX        X XXX
XXX          XXX
XXXXXXXXXXXXXXXX
_ - floor
= - bridge
^ - pressure plate
h = hatch
X - wall
The plate is linked to both the hatch and the bridge. Hatches open immediately, bridges have a 100 tick delay. So the lead goblin triggers the plate and the hatch pops open. Goblin skids to a halt to avoid falling down the hatch, then turns around to try another route (make sure there is another route in, a long and trapped one). Before he gets more than a few squares back across the bridge, it opens. Goblin falls to his death.