I'm wanting to make a sort of piston feed tape chamber, a 12x12x12 cube of blocks, that slowly gets fed into a piston feed tape. So the blocks would look something like this: 
And I'd like to pick out one block at a time, to move into a feed tape. The idea behind this is this will feed into my nether star farm, without requiring an AFK player to place soul sand.
I've tried various things, but not got anything really close, or worth sharing. I thought about using pistons on top to push down, and then fill up the spaces with a cobblegen, but the problem was I couldn't get it to work without the cobble coming through before all the soul sand.
Does anybody have any ideas how I can do something like this?
Best Answer
I don't have a good solution for the cube. I believe the best you can do is a quarry-like contraption where you extract strips of the cache block using flying machines, then reshape them into movable lines, align with input of your feed tape and push them into it. It's a complex slimestone contraption and I'm not good at these.
What I have, is a 4-tileable vertically 2D cache.
The composters in my cache are displaced gradually by a line of smooth stone. The stone generator attempts to push wherever there's room; it's already at its 12-block push limit so it can't destroy the pattern in the cache.
The composters form a 11-wide floor of arbitrary length. The jagged pattern on one side is not necessary - but without it some cycles of operation the cache just won't feed a block, filling a gap in the pattern instead.
The side pistons are alternating every other block per side. Underneath the space in front of them there are slime/honey sideway pushers. The operation is as follows:
Thus the composter travel in a packed S-pattern. At the end of the line they are pushed out from the line vertically: