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[John Johnston]

But you mention using upright bridges to prevent the obsidian from binding to the natural walls. Why can't we just do that with the OP's idea? I would've sworn he mentioned doing that, but it appeared to be discarded though I can't find where, or why.

I didn't use it in my test rig because I thought that the obsidian formed would stick to the floor under the bridge.  However I didn't really understand the principle.

What I now imagine is that you would use retaining bridges which are held only at one end, like this:

Code: [Select]

#######a#
bbbbbbba#
#c#####a#
#c#####a#
#c#####a#
#cddddddd
#c#######
But I'm not sure how you could then have a retracting bridge in the centre that wouldn't involve a floor tile present somewhere.  Anyone?

(edit)
What a bunch of bridges like this could do is create a vertical tunnel through which water and magma could fall at the same time.  Hmm.  Maybe.

[AlienChickenPie]

You could avoid the support issue by making sure the obsidian projectile doesn't touch the floor tiles supporting the bridges.
If you don't mind some afterbirth coming along with the projectile, you can create a room larger than the desired projectile and fill it with water. If you drop magma only on the interior squares that don't touch the walls, you'll be able to drop the projectile along with the water without worrying about any support issues or installing more than one drawbridge in the trap.

[John Johnston]

You could avoid the support issue by making sure the obsidian projectile doesn't touch the floor tiles supporting the bridges.
If you don't mind some afterbirth coming along with the projectile, you can create a room larger than the desired projectile and fill it with water. If you drop magma only on the interior squares that don't touch the walls, you'll be able to drop the projectile along with the water without worrying about any support issues or installing more than one drawbridge in the trap.

That's roughly what my original design involved.  What I mean by the support problem is this - when you place a raising bridge, unlike a retracting one, part of it needs to be on a foundation, so there will always be some tiles that things could stick to.  By having long bridges, only the ends of which are used to contain the magma, that can be avoided, but then how do you put a bridge to hold the magma?  I don't think you could support a retracting bridge just using other bridges at the sides of it, so somewhere at the edge of any retracting bridge there is always going to be a tile of solid rock which the obsidian could potentially stick to...

...unless I'm making some basic mistake here.   

[Asehujiko]

Inspired by this topic i have decided to build a similar creation. The test setup will be built as following: A 3x3 room above me entraceway is channeled out and bridged over with a retracting bridge. Water will be pumped up from the cave river from one direction. A floodgate is installed to prevent flooding the tunnel upon use. A drain is installed on the other side, also with a floodgate. This will further reduce the mess downstairs. A 1 wide tunnel is dug over to the middle of the preperation chamber, channeled and hatched over and locked with a floodgate, leaving a single tile with a hatch on the floor. The higher tunnel is filled with magma, the internal gate opens, letting magma entr the dropping room and is closed again. Then the hatch is opened, dropping the tile of magma into the pool, obsidianizing the center tile.

Now there's 3 things that can happen:
1. The obsidian teleports through the bridge into the tunnel and imediatly causes a cavein there.
2. The obsidian smashes through the bridge and causes a cavein along with the bridge materials.
3. The obsidian rests upon the bridge until it's retracted after which it collapses.

One is by far the best case scenario. The drain feature will become unnesacery(how do i configure firefox spellchecker to help with english instead of dutch?) and the trap can be operated by staggered use of the magma channel openings.

The second is the worst but considering the power of the trap, an acceptable ammount of work. There will be a considerable "afterbirth" of water as AlienChickenPie put it so politely and to reload the trap, the bridge must be rebuilt and both rooms flooded again.

The third makes maintenance alot easier and it allows for the trap to be preloaded long before invaders arrive. Drop magma, close magma hatch, reload magma chamber, drain excess water and wait. The trap can also be snapfired without draining water is case of an emergency and can be reconfigured for both water and magma flooding. Not reccomended for encasing purposes because of the risk of the tube clogging up.

The trap can be resized at will as long as the lower room is always one tile larger in all directions as the one above. However, load times increase exponentiay unless you use a vertical fluid storage, which will give you multiple uses before the whole thing needs to be recharged. Non-issue with theory 2.

Crude paint sketch:

[AlienChickenPie]

No, you're completely right. It seems like you can only completely remove support from below, which means you can't rely on drawbridges temporarily supporting the sides, because their foundations will always be there.

Has anyone attempted a method that only requires support from the bottom? Does the obsidian actually stay in place, or does it fall down immediately after it solidifies regardless of the water's position? If it falls down immediately, does it smash the bridge on its way down?
Now, if this method works, you could combine both to create a superdwarvenly obsidian trap. It goes like this- Enemies are herded into a room with drawbridges serving as the floors and walls, where they're encased in obsidian. The bridges retract, leaving the block hanging on the bridge supports. A second obsidian mold, located above the first one, uses the bottom support only method to create an obsidian block as big as the first one. This block is dropped on the first block, which sends both of them tumbling down into a conveniently placed chasm.

[mkbunday]

Why not have two tubes, one of lava, one of water suspended in mid air, so that they are facing each other with the exits one tile apart. When you open the floodgates, the water and magma meet in the middle, and then drop down. Viola? I don't see where bridges fit into all of this.

Code: [Select]

#####################
wwwwwwwwwwXLLLLLLLLLL
##########X##########
         # #
          g

# Wall
w Water
L Magma
X Floodgate
g Goblin


[Asehujiko]

That way the obsidian will clog up the shaft in seconds and you get to excavate multiple z levels of it with alot of scaffolding involved. Or the obsidian will immediatly latch onto the walls of the tubes and do absolutely nothing but cause you hassle.

[AlienChickenPie]

1. The obsidian teleports through the bridge into the tunnel and imediatly causes a cavein there.
2. The obsidian smashes through the bridge and causes a cavein along with the bridge materials.
3. The obsidian rests upon the bridge until it's retracted after which it collapses.

This is the million dollar question. Does anyone have relevant test results?

[Doppel]

Well, according to my tests a bridge will never support an obsidian block, it will just appear to do so due to the obsidian block latching itself to the floors beneath the wall bridges.
Thus 3. is out of the question, sadly.
1. Is also out of the question cause any obsidian block that by chance didn't latch itself onto the floors supporting the wall bridges (via solidifying on that particular z level) will smash through any bridge destroying it.
Thus, in case of the block actually not latching itself to the floors then 2. is true.
The weird part though is if the Obsidian block solidifies and latches itself onto the floors where also the bridge (and above it the other bridge) is located because when that happened not a single bridge got destroyed and infact said bridge could extract itself inside the obsidian block (think clipping). The bridge located one z level above the obsidian block (thus when you see the obsidian block floor) which retracted itself into the process thus also didn't get destroyed and sadly this prevents you from channeling the obsidian block.
Thus the best result you can wish for in this test is when the obsidian block solidifies and does not latch itself onto the floor sides of the lowest bridge (and thus subsequently smashes itself through that particular bridge, which really isn't that big a deal seeing that you can easely quickly rebuilt the bridge afterwards) and falls down the pit (which is say 15 z levels deep, thus more then enough reloads until you will have to mine it all out again).

Edit: also, this test appears to only produce an overly complex trap system which instead of simply smoldering them or dropping them into a watery doom rather traps the intruders inside cooling magma in midair. Apart from this simply being wicked cool, its also actually very handy seeing that it keeps items and corpses nicely stored inside the obsidian nicely deep in the selfdug pit for you to be mined out whenever you want to.

[AlienChickenPie]

How does it manage to trap them in mid air? You said the magma solidifies and then crashes through the bridge.

[Cheshire Cat]

This whole business of trying to form a block of obsidian and then drop it sounds extremely hard.

if you want a slower to reload solution, just use floor grates (bridges don't work) supporting a block or section of floor above the area you want squished. floor grates can be withdrawn using a lever or pressure plate, and will drop whatever they were supporting. most forts i build have some kind of entrance trap like this, with either floor grates or supports. i often tunnel them out of the existing rock. you can stack them on top of each other in a big vertical shaft or tower for multiple uses. tends to kill anything directly underneath, and stun everything else for your unskilled military dwarves to stab.

its one of my favorite methods of disposing of large nasty things like megabeasts and demons.

you can do it like this -

XXXXXXXXXXXXXXX
X     I           I     X
X  XXXXXXXXXX   X
X     I           I     X
X  XXXXXXXXXX   X         
X                       X
         &    &  &       
XXXXXXXXXXXXXXXX                 
X    optional hollow X
X         or pit         X           
X                         X   

X = stone
I = support
& = tentacle demon

you can collapse each single level on top of the nasties, or trigger the top supports to send all of them down at once with a high chance of said enemies going over the chasm or just flat out being crushed. there are hundreds of variations on this, though most require work to reload. i like to hollow out the level below to make things more spectacular as well.

next time i do a big fort i may try out this magma-water-obsidian block idea, though.

[KrataLightblade]

Has anyone considered using a Support from the top of the obsidian chamber?

Link the support and the bridges to the same lever.  When the bridge retracts, the support blows, and the Obsidian falls, witout taking out the bridge, thus meaning all you need to do is build another set up stairs up, put in a new support, get rid of you stairs, and bam, new Obsidian deathchamber.

[John Johnston]

I had an idea which isn't directly helpful, but might have other uses - at present I think we've established that magma can be contained on 4 sides without risking obsidian sticking to anything, but cannot be contained on the top or the bottom.
However, if instead of using a retracting bridge on the bottom, we used a series of 1 tile wide raising bridges on the z-level below, the tops of those bridges (when raised) ought to block the magma from flowing downwards.
It wouldn't be useful for this trap, as obviously the bridges would be in the way of anything underneath them, but it might have potential for messing around with.

[AlienChickenPie]

Has anyone considered using a Support from the top of the obsidian chamber?

Link the support and the bridges to the same lever.  When the bridge retracts, the support blows, and the Obsidian falls, witout taking out the bridge, thus meaning all you need to do is build another set up stairs up, put in a new support, get rid of you stairs, and bam, new Obsidian deathchamber.

That's awfully complicated compared to putting up a new bridge.

[MagicJuggler]

If playing on an arctic map, you can build a meaner projectile trap by merit of using water and bridges to form ice cubes. Have fun.