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[weenog]

Like the topic says.

I want to make something like a goblin grinder that runs intruders back and forth through the same trap area by closing one path and opening another at the opposite end.  I want to use a lever instead of a pressure plate as the trigger mechanism, because I need to be able to use it against husks (which retain their immunity to the fortress' traps if they're former fortress members).  I prefer to use drawbridges instead of hatches because I want them building destroyer-proof, and I want them to block paths for flying enemies, too.

Can I do this?  How?

I know it would be simpler to have 2 levers instead of 1, but I only have 8 living dwarfs in the fortress and they're very busy.

[Merendel]

you could probably rig up something with fluid logic.  It wouldnt be instant however.   you'd need ot rig up levers to turn on/off pumps that moved water onto or off of a preasure plate.   geting it to be repeatable would be a pain but probably could be done with a bit of clever design.

[Bumber]

From what I understand reading other threads, you can set one of the bridges up so that when it's closed mobs can use it as a wall to climb a ramp. Thus its 'closed' state is actually 'open'. It requires an extra z level, so it may or may not work with what you have planned, but it seems really simple and easy to make.

Flying enemies can be blocked by an additional bridge that forms a ceiling over the ramp.

[Putnam]

Can't you link it to one, pull the lever, then link it to the other?

[FuzzyZergling]

Can't you link it to one, pull the lever, then link it to the other?

I'm pretty sure that levers send a signal to raise when pulled in one direction, and a signal to lower when pulled in the other direction, not a signal to change from raised/lowered to lowered/raised when pulled in either direction.

So if he did that then pulling the lever wouldn't cause the second bridge to raise, since the lever is sending a signal to lower and the bridge is already lowered.

[weenog]

Can't you link it to one, pull the lever, then link it to the other?

Tried that before.  One ignored the first lever throw, then they raised and lowered in unison afterward.

[Merendel]

Can't you link it to one, pull the lever, then link it to the other?

Levers dont send a pulse of "Do something" signal,  they send either an on or an off (aka open/close) signal.    if a lever says open and the bridge is already open it wont do anything.

[weenog]

I wonder if I could get away with two quick lever pulls in succession.  Maybe the second signal would be ignored by each bridge if it came fast enough after the first was sent.

[Sutremaine]

It's possible, but if all you want is one path open when the other is closed then it's much better to use a retracting bridge and a raising bridge (as mentioned by Bumber). The retracting bridge is built over a ramp, and the raising bridge is built in a corridor.

Before the lever is pulled, the retracting bridge blocks access and the raising bridge permits access. Pull the lever, and both bridges change states at the same time.

If you want the lever pull to start or stop a repeater, minecarts are probably the best option. Fluid logic works, but it needs power and pump components.

[JAFANZ]

The wiki page on Bridges (IIRC, could be "Fortress Design" or "Security" though) explains it better than I can, but if you design you trap-route so that the area the bridge controls is on 2 levels, you can set it so the bridge being down means "Route A is open, Route B is closed", & up means "A closed, B open", meaning you can have 1 lever (& 1 bridge) controlling 2 states without worrying about water or minecart logic gates (as, technically, you've made the bridge the logic gate).

As an added bonus, these means you never accidentally have both routes open or closed at the same time, & the delay is always synchronised.

[kingubu]

Floodgate or door has opposite opening logic of a raised bridge.

[Sutremaine]

Floodgates and doors aren't building-destroyer-proof.

[WhimsyWink]

The wiki page on Bridges (IIRC, could be "Fortress Design" or "Security" though) explains it better than I can, but if you design you trap-route so that the area the bridge controls is on 2 levels, you can set it so the bridge being down means "Route A is open, Route B is closed", & up means "A closed, B open", meaning you can have 1 lever (& 1 bridge) controlling 2 states without worrying about water or minecart logic gates (as, technically, you've made the bridge the logic gate).

As an added bonus, these means you never accidentally have both routes open or closed at the same time, & the delay is always synchronised.

I think this means what I was going to suggest ... in closed position one could expose a ramp down to exit

[fricy]

@Weenog: Imho Bloodbeard's and Tinypirate's logic switches are the best for this purpose.

Simply build a changeover switch:


Connect the bridges to the pressure plates (purple arrows) then link the control lever first to one of the gears, pull it, then link it to the other gear. The two gears will be out of sync, a lever pull will switch one of the rollers to on, the other to off, and the two minecarts will change pressure plates. One of the bridges will open ~100 ticks after the lever pull, the other will close in ~300 ticks.