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I'm trying to create an elevator, but I'm stuck at powering them. I have inputs for each piston, but I can't seem to separate them. It seems that the redstone powers the block beneath it, and all 3 pistons are extended.

p 
p - rt
p

Is there a way to power pistons that are on top of each other? I am trying to avoid powering of the lower piston in the picture below.

enter image description here

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1  
I think a screenshot or two would help immensely - I can't really tell what you're trying to do here with just a diagram like that. –  Unionhawk Dec 2 '13 at 19:26
    
ok, i'll make one now –  Bartlomiej Lewandowski Dec 2 '13 at 19:29
    
@Unionhawk added picture –  Bartlomiej Lewandowski Dec 2 '13 at 19:33
    
I only see two pistons extended. Thought the issue was that three were extended? In the configuration you've shown, I would only expect two to be extended, not 3. –  John Dec 2 '13 at 20:05
    
@John Yes, but the problem still applies, since I am looking for a way to power only the middle one. –  Bartlomiej Lewandowski Dec 2 '13 at 20:09

4 Answers 4

up vote 4 down vote accepted

Pistons are weird. Let me rephrase that: redstone is weird. It never behaves how you would expect it to, consistently. This is especially the case, however, with pistons.

Here's one example:

Pistons versus lamps 1

As you can see, the redstone lamps transfer power in a normal manner (solid block receiving direct power will power the adjacent blocks indirectly). The pistons, on the other hand, behave a little strangely. The first extended piston is powered directly, so it extends. The piston below that one is receiving power indirectly from the block that the redstone is placed on (the lamps behave similarly if you take away the middle lamp). But where the heck is that bottom piston getting power from?

Apparently, pistons can receive power diagonally, or from two blocks above. It was considered a bug for a long time, however, it has since been marked as "Works As Intended". There's a more specific bug report here as well.

Even adding a block in between the redstone and the piston doesn't fix it:

Pistons versus Lamps 2

So how do you fix this? Well, that depends on your intended design. If you're going where I think you're going, and going for something similar to a zipper elevator, you actually don't need to worry about this; the zipper design works despite the fact that pistons are activated 2 at a time. Otherwise, you might have to adjust your design, since no combination of blocks and redstone will power just one piston in a vertical tower of pistons. It all depends.

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The developers right now: "We have no idea how to fix this" "Let's say this is a feature." –  Bartlomiej Lewandowski Dec 3 '13 at 18:32
    
@BartlomiejLewandowski The biggest thing is that they don't want to make the redstone community angry by breaking everything that utilizes this (BUD switches, etc) –  Unionhawk Dec 3 '13 at 20:14

Due to diagonally powered pistons, this is impossible.

Diagonally Powered Piston

No matter how you try to power the center piston, it will always power the piston below it.

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Not even with repeaters? I know you can't stack two, but from two sides? –  Orc JMR Dec 3 '13 at 14:05

redstone travels though a single block, so in order to fire off only one piston, you would need one block between the torch and the piston. Whats happening in your setup is the redstone hits the piston, then travels through it to the other piston.

solution: P = piston, S = Stone(or any solid block), RT = redstone torch, RS = redstone dust

like so:

P
P S RS/RT 
P

this setup should only fire the center piston, but as brought to my attention in this answer's comments.. is not the case. so you can try this, but dont expect it to work.

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1  
I beg to differ. Diagonally powered pistons are so much fun. –  Unionhawk Dec 2 '13 at 21:23
    
hm, thats interesting... I don't recall pistons being that unruly, because it does work with every other redstone powered machine... break the block next to the lower piston –  Rapitor Dec 2 '13 at 21:28
5  
No effect. If you remove the center piston, then the bottom piston becomes a BUD. It's getting power diagonally, which in pistons, and sometimes dispensers and droppers, causes strange behavior. –  Unionhawk Dec 2 '13 at 21:31
    
I see, well I edited my answer to show it probably wont work. –  Rapitor Dec 2 '13 at 21:37
    
Stupid BUD switches! –  MBraedley Dec 2 '13 at 21:39

There are a number of ways to "force" the bottom piston to not move. You could use Obsidian, you could use a big stack of blocks, or you could use an opposing piston. Here's an example that might get you closer to where you're going for your elevator. Not quite the design you requested, but it does work so that only a single piston at a time is moving.

Before the switch is thrown: enter image description here

And after: enter image description here

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