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I like to mess around with pointlessly complex mob killing contraption for the enjoyment of my kids. I built a redstone contraption at a spawner the other night but it didn't quite work like I planned. I'd like any comments you might have had with the same behavior in order to try and figure out what got bent.

Basically, the contraption uses water to push all the mobs from a zombie spawner towards a one block wide hallway. This hallway contains a series a of stone pressure plates and pistons that push the mobs over the edge of a drop into a small holding pen for disposal.

The problem I encountered was that the mobs would walk onto the pressure plates, even when there was no obstructed path to me except for the plates themselves (hard mode)! It's almost as if they knew it was a trap.

(The Mob behavior itself, though random - I know, was quite funny.) They would stop on the block before the pressure plate and then look around as if they were trying to path around. They would often shake their heads "no" as if they were saying they wouldn't walk into the trap. They would turn around and shove back at the mobs stacking up behind them. (My kids had a ball making up dialogue for them)

How tall is that hallway? I'm thinking if it's only 2 tall, the game logic may see it as unpassable with the addition of a pressure plate.

I've seen this, too.
It made me completely over-complicate my proximity detector.
...And it was in a 3-high room.

I have no idea how to fix it. ._.

try wood plates? Im annoyed by the monsters supposed to be pushed off my pressure plates, but instead get suffocated by the piston. Of course, its drop then stay on my pressure plate and screw my ginder up...

In the hallway, is it possible to use water to push the mobs onto the plates? Use signs as needed to keep the water contained where you need it.

A 2 block tall room should be sufficient. I use a mob grinder that has monsters spawning on stone pressure plates in a 2 block tall space. As soon as they spawn, the pressure plate activates a piston and pushes them off. Your solution is simple if you have the room. Just make a 1 or 2 block drop off at the end of your water stream. The water will push the mobs off the edge onto your pressure plate. That should stop them from glitching out. Its unlikely this problem is mob behavour related, as we still have the "dummy" AI system and they don't pathfind at all yet, they just walk in the shortest line towards their target...for the most part

I did some more experimenting last night and I think I have demonstrated that the mobs will not walk onto pressure pads (though, as Springy notes, they can be pushed.)

Even whent hey had full opportunity to walk through a hall to get to me, they would not proceed until another mob pushed through behind them.

I did some experimenting as well. I made a 20 x 20 square around me made completely of pressure plates out in the open desert. While it seemed to me that the mobs really just could not see me as long as I stayed inside the square, if I left the square momentarily and attracted their attention they then had no qualms at all about walking over the pressure plates to get to me inside the square.

ETA: My second experiment using the same square clearly demonstrated to me that the mobs were, in fact, able to see me even when I did not step outside the square and they all willing walked over the pressure plates to attack me.

The nature of the hallway has to have something to do with the results you're getting.

Interesting - could you PM me your exact methodology so I can try to pin point what it is about the hallway that is blocking them?

Quote from electricblooz

Interesting - could you PM me your exact methodology so I can try to pin point what it is about the hallway that is blocking them?

Basically, it was just a wide, open desert flat area in a normal world (not superflat) where I laid a 20 x 20 square of stone pressure plates all around me so that there was no way to get to me from any direction unless they walked over the pressure plates. I put down a few torches inside the square of pressure plates so that mobs wouldn't spawn inside it and I walked around inside the square with my stood my sword at the ready until night fell. The first time, it seemed like I had to step outside the square to get the mobs attention, but the second time I was able to easily lure in about 5 zombies, 2 skeletons, 1 spider, and a creeper without leaving the pressure plate square. (A creeper ended the experiment both times by blowing up inside the square (lol - I still suck at fighting them out in the open with just a sword).

I think now that the reason for the trouble I had the first time was that I had my torches inside the square a little too close to the edge of the square so the mobs were spawning a little farther out and they didn't lock in on me until I got a little closer to them.

I was, however, on Easy mode, not hard.

ETA: Came back inside for a break and re-did the experiment on Hard. Same results right down to a creeper eventually blowing up the area - lol.

I too am a fan of complex mob killers electric ;). My idea will work, but you are right. They have to spawn on, fall onto or be pushed onto pressure plates. I have some nasty ones to share with ya if you want, or if you would like a second set of eyes for yours, hit me up I'll be on tonight.

finally got back on and did some more testing. It appears that the 2-high corrodor was the problem. I busted out the roof and the mobs immediately started walking right through the channel.

However, interesting behavior, it appears that the mobs try to "hop" on to the pad instead of just walking onto it. (hence the reason the roof was the problem). This created another problem with the trap in that the hop would cause the mob to glitch through the extending piston (allowing them to slip through.

So, I've got more design work to do (which is fine) and we have id'd a behavior.

Quote from Cobra951

How tall is that hallway? I'm thinking if it's only 2 tall, the game logic may see it as unpassable with the addition of a pressure plate.

Called it.

Glad you fixed it.