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[Gatleos]

Alright, I've been at Dwarf Fortress for a while now, and built my share of complex machinery, including magma pumps, power plants, repeaters, etc. Right now though, I'm trying to construct a long retracting bridge at the entrance to my fort, something like this:

O = Wall
7 = Lava Moat, 1 Z-level Below
~ = Bridge
^ = Trap (Explained below)

  O777~~~777O
  O777~~~777O
  O777~~~777O
  O777~~~777O
  O777~~~777O
  O777^^^777O
  O777~~~777O
  O777~~~777O
  O777~~~777O
OO777~~~777O
^~~~~~~777O
^~~~~~~777O
^~~~~~~777O
OOOOOOOOOOO

Enemies enter in the lower left, my entrance is beyond the top. The traps in the lower left are pressure plates, only activated by enemies. The pressure plates cause the bridges to retract. The traps near the center are weapon traps. The bridges are anchored on those squares, so if an enemy happens to be standing there when the bridge retracts, they will either be stabbed to death or dodge into the moat.

Any suggestions on improving the design would be appreciated, but the real question I have is this: is there an efficient way to create a system that would react to the bridges retracting, then reset the signal (and the bridges)? The inherent problem with using the pressure plate is that an "off" signal is sent as soon as the goblin steps off of the switch. If the pressure plate activated another water-clock-like device, it might work. Any suggestions?

[SkyRender]

It'd be more efficient to have the bridges be lever-operated, especially if your fort has children or nobles in it.  Just stick the lever in your main meeting area and when the Goblin menace pulls up to your gate, pull the lever!  It's not fully automated, but really, getting a fully automated anti-Goblin system in place is almost impossible thanks to Murphy's Law.

 Also suggested is that you have a roof over the passage.  Bridges can and will fling anything on them into the air, and a floor or wall on the Z-level above will prevent them from flying into the stratosphere and potentially into your fortress by accident.

[existent]

Build two entrances, both identical as you illustrated (or perhaps mirrored). When you hook up the bridges, attach them to the other entrances pressure plates as well, but on the opposite setting. That way, closing one (and killing the invaders) resets the other.

[Gatleos]

  OOOOOOOOOOO
  O777~~~~~~^
  O777~~~~~~^
  O777~~~~~~^
  O777~~~777OO
  O777~~~777O
  O777~~~777O
  O777~~~777O
  O777~~~777O
  O777^^^777O
  O777~~~777O
  O777~~~777O
  O777~~~777O

        FORT

  O777~~~777O
  O777~~~777O
  O777~~~777O
  O777~~~777O
  O777~~~777O
  O777^^^777O
  O777~~~777O
  O777~~~777O
  O777~~~777O
OO777~~~777O
^~~~~~~777O
^~~~~~~777O
^~~~~~~777O
OOOOOOOOOOO

So, I could block off one path with floodgates and the other with a 1x3 drawbridge, ensuring that their signals are out-of-sync. When one opens, the other closes. The problem remains, though: how can this work with pressure plates? The signal will just switch back after the invaders step off the switch.

[existent]

Oh, I see. I didn't understand the question. I wouldn't know how to do what you want.

[Vizx]

You could have the pressure plates activate a floodgate that releases water onto another pressure plate (this one linked to the bridge), then just reset it by lever.

[JAFANZ]

As an alternate to the above (which I believe could be turned into a water-clock by not dropping a full 7/7 onto it), you could split your route in two (or three) at an early point, with drawbridges at approximately the same point on each of them, with the triggering pressure plates between 50% & 75% of the way to the bridges, raising one should cause everyone using that route to recalculate to the other bridge, & not recalculate the original route until the subsequent bridge is raised.

Each route should be a little longer than the previous, so you have control over which order they are preferred. If using more than 2 routes, the entrance to each subsequent route should be from inside the route you wish to path to it from, set this up correctly & it may be possible to send them into an infinite loop, that is nonetheless still open to more suckers.

Another thing I'd note is that you might want to put a pillar on the middle of the 1st set of tiles for the Goblin army route, so friendly caravans don't use it, make their (apparent) default route rather long, & then when they're a little way in, trigger the opening of a shortcut (until they pass through, then close it again).

Of course I haven't actually survived an embark long enough to experience caravans or sieges myself yet (I may have to turn cave-ins off...)

[Gatleos]

I was thinking of connecting the pressure plate to a gear assembly forming the connection between a windmill and screw pump. Whenever the pressure plate is toggled, the gear assembly toggles too. The screw pump activates for a few frames, squirting water onto a second pressure plate (water-activated). The water flows out into a corridor and evaporates. When the second pressure plate is dry, the bridge extends.

Phew.

[Sphalerite]

If you have a bridge triggered by a pressure plate just in front of the bridge, the pressure plate will when stepped on send a retract command to the bridge.  Bridges have a 100 cycle delay on retracting, so the enemy should have time to move off the pressure plate onto the bridge before the bridge retracts and drops him into the moat.  About 100 steps after that the bridge will then extend, since nothing is standing on the pressure plate anymore.  That would seem to be what you want in this case.

Your fist problem may come if a goblin or something remains standing on the pressure plate, which will cause the bridge to stay retracted and not let anything step onto it.  To solve this problem you can have the pressure plate trigger the control inlet to a water-powered repeater.  You can use a simple design like the following:

Code: [Select]

WWWWWWW
WX^BX..
WWWWWWW

where a supply of infinite water is connected to the right side.  The rightmost X is a floodgate connected to your invader detecting pressure plate.  B is a single-tile raising drawbridge.  ^ is a pressure plate set to trigger for water of 5/7 or deeper depth, and the X on the right is another floodgate, which along with the single-tile bridge is connected to the water-detecting pressure plate.  You then connect your invader-dropping bridges to the center water-detecting pressure plate.  This will cause the bridge to cycle on and off if anything is standing on the pressure plates at your fortress entrance.

The other problem you may have is due to the fact that you have three invader-detecting pressure plates connected to the same output devices.  Because of the time delay on pressure plates, the fact that they only send open/close commands when triggered and not continuously, and the fact that bridges and floodgates ignore open/close commands during the 100 cycle delay between triggering and activation, you can end up with a situation where pressure plate triggers are ignored and the plate gets out of sync with what it's triggering.  It's safer to have a system where during invasions you only have a single tile goblins can enter through and put the pressure plate there.

[Altaree]

A slight modification to Sphalerite's set up will allow goblins to trigger the bridge open but then require you to pull a lever to close the bridge again.

Code: [Select]

WWWWWWWW
WvX^XD......
WWWWWWWW

1) Pressure plates in the hall are connected to the right most flood gate (X).
2) Lever to enable the device is connected to the door(D) (safety switch)
3) Pressure plate(^) is connected to the bridges and set to 6+water
4) Lever connected to left floodgate to drain the above sequence
5) pit to allow water to leave(v) to a drain or water crusher.  Could even be two floodgates on the left that you open and close a couple of times.

[claer_runway]

Also suggested is that you have a roof over the passage.  Bridges can and will fling anything on them into the air, and a floor or wall on the Z-level above will prevent them from flying into the stratosphere and potentially into your fortress by accident.

...and presumably explode in gore. problem?

[Sphalerite]

Bridges can't fling creatures up onto higher Z-levels.  Objects can be flung upwards, but creatures flung by bridges always stay on the same Z-level, at least until they start falling.

[deoxys413]

Why not just go for a single wide bridge filled with weapon traps? Only those with epic dodge will make it then they have to deal with a cage trap to deal with afterwards.

[existent]

Why not just go for a single wide bridge filled with weapon traps?

I for one always favor awesome-osity over practicality.

[deoxys413]

Why not just go for a single wide bridge filled with weapon traps?

I for one always favor awesome-osity over practicality.

Fair enough. I do suppose I've lost touch with my dorfy side of late.