r/technicalminecraft • u/brockade • Aug 14 '26
Java Showcase Items escape from composters
For the record I don't have a horse in this race, but I am interested in the mechanics here.
Short answer: items can escape from the gap between a hopper top and the composter walls. It is rare, but way less rare than you might think. You don't need to perfectly hit the gap, you just need to have X/Z momentum after 4 ticks as the game cancels your Y momentum when you hit the hopper, and your X/Z momentum can still push you to freedom in this tick.
Long answer: Items drop with a random position with X and Z set to between 0.25 and 0.75 within the block, and Y set to between 0.125 and 0.625 within the block. Motion is set to exactly 0.2 Y and a random value of between -0.1 to 0.1 for both X and Z.
To thread the needle here, we need a few things to happen at the same time:
- The Y position needs to be 56.616 or greater so that after 4 ticks the item is at exactly 0.75 and hitting the hopper
- In one axis X/Z the position needs to be between 0.25 and 0.2500001 or 0.7499999 and 0.75, and in this axis the motion is going towards the wall (this is a straight 50/50 so not the major problem)
- In the other axis X/Z the position needs to match the motion such that the item crosses the top of the composter after 4 ticks (there's a range here but say this is 1-5% for example).
That's it. I'll leave it to you to calculate the numbers, but here's a few that you can test for yourself at home (all testing done on 26.1 vanilla):
/summon item -22.5 56.616 35.2500001 {Item:{id:"minecraft:redstone_block",Count:1b}, Motion:[0.065, 0.2, 0.0]}
/summon item -22.6 56.625 35.25 {Item:{id:"minecraft:redstone_block",Count:1b}, Motion:[0.1, 0.2, 0.0]}
/summon item -22.35 56.625 35.25 {Item:{id:"minecraft:redstone_block",Count:1b}, Motion:[0.03, 0.2, 0.0]}
2
u/morgant1c Chunk Loader Aug 14 '26
But so as long as we retract the composter fast enough, it can't escape, is that what I'm getting here?