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Is it possible to make a mob farm with a cactus grinder in the current Minecraft version (beta)? And if so, what would a basic general layout be? I have seen pre-beta versions, but one patch changed the behavior of cactus, so they don't work/grow as before.

Yes, I realize lava grinders are all the rage :) I'm just wondering if cactus still works - I've played around with it, haven't quite gotten it to work yet.

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up vote 12 down vote accepted

It is entirely possible and I built all my grinders this way (before the introduction of XP, which makes it less desirable to kill monsters, and hoppers, which can rescue items from all sorts of death traps). The key is to place the cactus one block above the water and use diagonal flows. This is a picture of the grinder of my main mob trap, but this design is also suitable for installing in one corner of a dungeon wall to grind on a mob spawner (especially if you mine the floor of all mossy and plain cobblestone, leaving a slot perfect for the water flow).

Cactus grinder

Mobs are pushed against the sand block by the water. Once they randomly jump up and stand on the sand block, they are eventually killed by the cactus. Their drops then usually land in the water below. The water's flow splits evenly around the sand block and rejoins at the other side where the flow goes to the collection point.

Restricting the cactus to be two blocks high as in this image means that the grinder also generates a modest supply of cactus blocks.

Originally, I stood at the point where the flows rejoin to collect items, but a creeper somehow blew up the trap while I was AFK, and I had problems with chickens pushing me out of the collection area, so after that I had the items carried some distance away in an aqueduct (this was before hoppers).

This particular installation is for my main mob grinder, so besides the cactus there is also a fatal drop from above; the cactus here is merely to kill the ones that the water saves from instant death.

You can visit this trap and my other cactus traps at my Minecraft server at mc.switchb.org; take the Nether route to the “old base”.

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You might want to add a direct link to your Minecraft Topics into your post, it has some good suggestions there. I like the one to use glass blocks to stop incoming lava (or water) so you can see what's blocked, later. And the shovel-only mining concept is interesting, I may have to try it. –  Cyclops Feb 22 '11 at 14:25
    
I thought about doing that, but it would be general self-promotion which is disapproved of on SO (see the rule against signatures), since it doesn't say anything about this problem I didn't say here. –  Kevin Reid Feb 22 '11 at 15:24
    
Ah, I didn't think of that. I was going to delete my comment once you added a link, guess I'll leave it up now. :) –  Cyclops Feb 22 '11 at 21:26
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I don't have my awesome unicode palette at hand, so this ascii map will have to do.

+------------------+
|~........#........|  . sand bottom with flowing water on it
|........#........~|  # cactus
|~........#........|  ~ water source
|........#........~|  - pit border
|~........#........|
+------------------+

The idea is that water pusher the mob against the cacti; eventually they'll be stuck there and die.

Here's a proof of concept: (I don't have the time to refine it)

enter image description here

  • Cacti are placed right where the water stops flowing (any farther and the trap wouldn't be effective; any closer and the water would destroy the cacti)
  • Light is added to attract the mob to the trap.
  • Small holes are added to the side to allow placement of cacti on the entire line; they're covered by...
  • An outward lip allows the mob to get in easily.

Where does this fall short?

  • Spiders can climb out. This is the only change in behavior I can think of from alpha; this can be solved through an inward lip.
  • The spoils of war are pushed against the cacti and thus destroyed. There's no real fix for this.
  • There's no easy way out for humans either. I think non destructive ways out can be provided via ladders (even if the mob could use ladders, they could be placed diagonally making for an harder to follow path). This however would weaken the idea of the inward lip (you'd have to make holes for the exit).
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Ah, I was looking for the cactus equivalent of a lava grinder/blade (which preserves loot) - this is more of a destroyer :) Do you mean that it's a property of using cactus (and thus cactus is not viable), or of this particular design? –  Cyclops Feb 20 '11 at 17:02
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Cactus has the property to destroy any drops that hit it, to resolve this in past cactus grinders, the catcus was placed where water would force the mob or spider into them, and the items would then be carried onward through the water into a collection point. Even in this design the cactus could claim some items based on basically when the mob dies how the item fell. ,, Wish I could site an example so this would make more sense, the basic concept should work in the changes but I havent used it in a while. –  Ward Feb 20 '11 at 17:38
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The YouTube user FreakEntertainer came up with a great design for a canal with cacti on the bottom, so the mobs will get damaged passing over it. This is great, because you can plan out exactly how many cacti to place so the final one will kill the mob, and the items will still flow out the end. (Zombies, Skeletons, and Creepers have 10 hearts each and cactus takes away 1/2 a heart, so you would need 20 cacti). Of course, if you want to ensure the cacti don't destroy the items, you could damage the mob and then make it fall down a pit.

The construction of the canal is explained in the video.

Image of the canal: enter image description here

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This is also a good answer, it was a tough call on the checkmark. :) –  Cyclops Feb 22 '11 at 14:27
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