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I'm trying to make a two level piston (i.e. when it is powered on it pushes blocks up two levels rather than just one). The way that I am doing it is placing a row of pistons on top of a row of sticky pistons. I've placed a power line to both rows of pistons, and connected it to a switch. My intention is that when the switch is fired on, both rows of pistons get activated. When powered off, they both fall down two their base elevation (they both lose power, so they both retract, and the sticky pistons on the bottom pull the pistons on top down with them).

The problem I'm having is this: for some reason the sticky pistons aren't pulling down the pistons on top. The pistons on top just levitate in the air above the sticky pistons. Does anyone know why this is happening (possibly a glitch)?

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pictures please? –  Jeffrey Lin Oct 8 '12 at 16:09

2 Answers 2

Sticky pistons can't move certain blocks, such as extended pistons. I'm guessing your second level of pistons aren't retracting early enough and are therefore not completing their retraction before the sticky pistons try to pull them.

The likely solution is that you need to add a delay to your circuitry which allows the upper pistons to retract first, then the lower pistons a couple ticks afterward. The problem with this is that you need them to extend in the opposite way, with the lower pistons extending first and the upper pistons extending afterward. You may have to use an ABBA switch to create this activation/deactivation pattern for you (extend bottom, extend top, retract top, retract bottom).

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I do have a delay in the circuit between the lower and upper level pistons, but the bottom row starts first. So I guess all I have to do is move the switch. –  Ataraxia Oct 8 '12 at 14:52
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@phoenixheart6: It may be more complicated than that. See my edit. –  gnovice Oct 8 '12 at 14:59

I ran into this problem myself while designing a portcullis. As gnovice correctly answers, extended pistons are one of the blocks that can't be moved by other pistons. The following redstone diagram was my solution to getting around it.

Two-level Piston Diagram

Note; there may be some confusion on piston placement - In [A] the pistons are placed on top of a raised block. In [B] the top of the second layer of pistons is below the raised (yellow) blocks, so that if [A] were to be powered the top of the unpowered [B] pistons would be flush with the surface the redstone sits on.

The power reaches the bottom pistons in [A] first, followed shortly by the upper pistons in [B]. When the power is turned off, the raised (yellow) repeaters in [A] will keep the power on the bottom row long enough for the upper pistons [B] to lose power and retract first.

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Off topic: Can we see your portcullis? :D –  John the Green Oct 9 '12 at 0:04
    
Sure; just waiting for the rain to stop so I can get decent screen shots. Note that the end product involves two of the mechanisms, one at the top, one at the bottom. The top one is altered a bit ([A] on top [B] on bottom), but is essentially the same wiring. –  Trent Hawkins Oct 9 '12 at 1:42
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