Interesting property I noticed about pistons. When they move a block it interrupts any ongoing breaking animation on that block.
If they move a block very quickly you don't have a chance to break that block, depending on how hard the block is and what tool you're using.
For example, here I hooked up a rapid pulsar to a sticky piston. The cobblestone it pushed was completely impervious to an iron pickaxe.
Next I tried a diamond pickaxe and even that was too slow to break the cobblestone.
If you made a wall of constantly moving blocks like this there would be no way to break it from this side, short of explosion. Sure you could just go around it and break the piston or the wiring...
So that got me thinking, what if you made a building with solid walls of rapidly moving piston animated blocks? The piston head could face outward, to stop people from breaking in, or face inward, to stop people from getting out. You could make a perfect cube with constantly moving ceiling, walls, and floor. There would be no way of getting around it.
People could stop the pistons from moving by putting 12+ blocks, or obsidian, in front of it. But that wouldn't let them break in or out since the blocks they add would just add a further barrier that would protect the pistons. As soon as that barrier is removed the pistons would start moving again.
Would this create a barrier that only TNT can break through? Is there any flaw in my logic?
i think i found a flaw in this. namely the corners where the two moving walls join up. that would have to have stationary blocks which can easily be destroyed and if that part is destroyed it will expose the pistons allowing a user to break them. i havent tried this so i dont know if the pistons will move the blocks to quickly or u will be able to break the pistons.
I figured this out in a thread when pistons first came out. I didn't find out much more than you already have except that you can walk through the back of the pistons when they are moving fast enough. So it would make for a one-way door.
Why not something like two PBM Arrays arranged in a fashion that creates a box, or a room, and that be set like a cell. Put it on the fastest setting and have both arrays rotate as fast as possible. One array of course would have to end up going above and below the other array, but other than that it would fit perfectly. Then it would seem like a room that was moving but it wouldn't actually move as such, and they wouldn't be able to break out without explosives.
The problem with rapid pulser is that it's too fast for servers (atleast from my experiences). All the torches will burn out, and voilah. You're free to mine. And an unmineable block doesn't really make sense in singleplayer