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I have created a vertical trap that uses water to drag unsuspecting creatures from the surface into a vertical pit, they literally fall to death.

Well, except chickens, and sometimes spiders.

Right now I have to open a door and enter the trap periodically to recover loot from the creatures.

I would like to set up a water "slide" at the bottom that would make items dropped by dead mobs flow with the water out of the trap and to where I stand. However, to do this I have to open one cube of the bottom of the trap for the water to flow through, and apparently that's enough for chickens to get past. I tried this, and when I got back from dinner, I had about 15 chickens flying around me, outside the trap.

I have created an elaborate drowning tool to handle chickens and spiders that survive, but this of course only works if the mob is still in the trap, and not roaming around outside, and I have to manually activate and deactivate this, so it's not automatic. However, if the spiders and chickens could just stay in the trap, I have no problems with activating this from time to time.

However, I don't want to go chicken-hunting in the cramped area outside the trap.

Is there any way I can set up such a water slide, get the items to exit the trap, without getting the outside of my trap filled with chickens?

Basically, the bottom of my slide, seen from above, was like this:

RRRR  <-- R is rock
R WR  <-- W is a water source, this will flow down and to the left
R  R
R  R  <-- vertical shaft is over
R  R  <-- this 2x2 area (the spaces between the rock)
R  R
R RR
RSRR  <-- S is where I stand

In this case, everything is covered up, except that the cube just above the S has to be open for the water to pass, and thus the chickens can escape.

Is there any way for me to get the loot, without opening up for chickens?

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Working on an answer too, but check out Etho's channel on Youtube. He just built a passive mob separator, and there are several tutorials on mob systems. –  Michael Aug 16 '11 at 13:16
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7 Answers

up vote 10 down vote accepted

put a slab on the square you are standing on and leave a 1 square gap in the direction the water is flowing from (use glass if you want to be able to see what's coming). The slab will prevent anything from being pushed through but you will automatically pick up the items as they approach.

Adding a picture to clarify:

Side view:

 G   W
UG   W
UG   W
SWWWWW

W = water
  = blank space
G = glass
U = where you stand
S = Slab

The chickens won't be able to move into where you are due to the half slab keeping them in the water tile beneath the glass.

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You mean that the S square, where I stand, put a slab, and stand on that, and then leave my opening as I tried it? If I understand that correctly, chickens would be able to enter the area in front of me, but not exit, because the slab would block them, but items would get close enough to me and with no barrier inbetween, so that I would pick them up, is that about right? –  Lasse V. Karlsen Aug 16 '11 at 13:23
    
Yes, the water stream will push the items right up onto the slab. –  Michael Aug 16 '11 at 14:25
    
Hm, the items float right up to the slab, but not onto it, and no matter how/where I stand, I can't seem to get them picked up –  Lasse V. Karlsen Aug 16 '11 at 14:37
    
But this gave me the idea on how to solve this, I'll post my own answer, but accept this. –  Lasse V. Karlsen Aug 16 '11 at 14:43
    
Hrm. I thought they went onto slabs. Bug maybe? I'll have to experiment with that. –  Michael Aug 16 '11 at 14:59
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I tried various of the existing answers here, and they didn't really solve anything.

  • The slab answer didn't quite work, but since it was the one that sparked my solution, I accept that one. In short, the items ended up butting against the slab, and was apparently just out of reach for me.
  • I did not get to check the auto-drowning system that Michael posted, it requires some extensive reworking of my current trap design.
  • The cactus idea doesn't work, as the cactus can't be placed like suggested (at least not in 1.7.3 beta)

However, what did work was to change the original idea just slightly.

RRRR  <-- R is rock
R WR  <-- W is a water source, this will flow down and to the left
R  R
R  R  <-- vertical shaft is over
R  R  <-- this 2x2 area (the spaces between the rock)
R  R
R RR
SRRR  <-- S is where I stand

The difference here, from what I had in my question, is that I am standing one square to the left of my original idea. However, since the water flows towards me, all items will end up in the corner butting against me, and are thus just in reach to pick up, even though there is a wall between me and them. This solved the chicken problem, as they now have nowhere to escape.

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5  
It's really nice that you accepted another answer because he lead you to discover the real answer, but that's not how this site works... the accepted answer should be the answer that solves your question. Upvote the other answer, or attribute a bounty if you really want to be friendly... but accept this answer if it solves your question. –  Konerak Aug 16 '11 at 20:18
    
yes, please accept your own answer since its the correct one –  z - Aug 16 '11 at 21:27
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One option is to remove the chickens from the rest of the mobs during their fall down the vertical shaft. Since chickens gracefully float down instead of plummeting to their doom like other mobs, a stream of water will catch them, whereas other mobs will fall through it. If you build a water stream like in this screenshot (the water is supported by signs), you can filter out all the chickens, and put them in a separate room (perhaps a egg farm).

In this example, the mobs would fall down the chute on the right, and the chickens would get caught on the water stream. The other mobs would pass through and fall into the right hole, but the chickens would float into the left hole instead.

enter image description here

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+1. This sounds like it would be an easy retrofit to an existing design. –  SevenSidedDie Aug 17 '11 at 0:01
    
I've seen a full-scale mob trap that used this design on YouTube. I don't remember the source though. Spawning pads up high, mobs fall down through a floating lake which chickens land in. –  Kevin Reid Aug 17 '11 at 0:57
    
This I have to try. Looks promising. –  Lasse V. Karlsen Aug 17 '11 at 6:53
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The answer is to use cactus. You need a one block large water slide. on both sides, put a cactus. When a chicken pass trough the slide, it will hit a cactus, and be pushed back on the second one, until it's death.

Top view:

RRRR
R WR
R  R
C CR <-- C is for Cactus 
R RR <-- You should also put a block above water here, if not already
R RR
RSRR
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+1 Oh, it is possible to keep the chickens out of the water slide. I sometimes get bored of walking down to my drop collector only to see that there is a chicken standing on the pressure plate. I'll remember to use a cactus or two next time... :) –  Tom Wijsman Aug 16 '11 at 13:22
    
This too sounds like a good plan, I will have to experiment with that as well. In terms of accepting an answer though, the one by yx_ answers it directly, so if his answer works I will accept his. However, I will definitely try cactus in my trap. However, the wiki entry - minecraftwiki.net/wiki/Cactus - seems to indicate that I can't have blocks adjacent to the Cactus block. I will look into how I can use Cactus as part of my trap but I think it will be hard to incorporate into the current design. –  Lasse V. Karlsen Aug 16 '11 at 13:26
    
@Lasse You may be right, I haven't used a mob trap for a while, cactus behavior may have changed since. –  Jupotter Aug 16 '11 at 13:32
    
Is it possible to instead place the cactus under the water near the end of the water slide where the water is the lowest? –  Tom Wijsman Aug 16 '11 at 14:00
    
It would be inefficient as cactus destroys items that come into contact with it. –  Timtech Jul 29 '13 at 16:45
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Your best bet is probably to build a drowning system, as chickens and spiders are one block high. This is my attempt; it probably could be better:

      B
B B W B B
B B W B B
W w w B B
B S   B B
B B W w w P

W = water source
w = water stream
P = pressure plate
B = random blocks - I like to use glass so I can see what's going on

This takes advantage of the mobs' dumb propensity for swimming up if they find water. They'll be dragged into the water column, swim upward and hit the ceiling. Being dumb they drown banging futilly on the ceiling, and their loot will fall down the hole to the lower water stream. In this setup the loot will fall on a pressure plate that also stops the water stream from speading everywhere.

This'll work for chickens. Spiders are a bit more complex because they are two wide. You'll need to make a diaganal water stream at the bottom of your 2x2 drowner, so that your loot will end up in the hole (Top view):

+---+
|W w|
|w  |
+---+

I'd put this "collator" one block below the widened system above, using signs to hold the water up above. There's probably a way to put it on the same level but I haven't though of it yet.

Ethos' tutorial on a drowning system

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however, to do this I have to open one cube of the bottom of the trap for the water to flow through, and apparently that's enough for chickens to get past.

Simply use a piston and a lever to block the flow of water when you don't need it.

Couple this with a high latency repeater cycle and you can trigger the piston door every so often (the actual time length depends on the length and setting of the repeaters; the pictured system cycles every ~20 seconds; you might want something longer).

enter image description here

This gives chickens no time to go through, while items slide through the trap only as much as needed for you to pick up.

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The point of my question was to figure out a way where I would automatically pick up any loot dropped from these mobs, if I went AFK. Since items disappear after some time, the piston idea, while neat, would be just as effective as my current setup. It's better than the design where I have to enter the trap though, but I'll still try to solve the auto-pickup problem :) –  Lasse V. Karlsen Aug 16 '11 at 14:39
    
@Lasse: That can be done. See my edit. –  badp Aug 16 '11 at 15:21
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One alternative way of ensuring that no chickens pass through your slide is to make sure that the source of your mobs has no lit grass for chickens to spawn on. While this probably isn't the sort of solution you're looking for, you might find it easier than redesigning and rebuilding your trap.

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