It's essentially impossible to make security through pressure plates doors/hatches/retracting bridges, basically because pressure plates and doors can get "stuck", a pressure plate wont reset until nothing has triggered it for a sufficient number of ticks. Hatches and retracting bridges can't get stuck, but dwarves can jump or climb when they open out from under them. This makes it like herding cats.
As loci notes, it's as simple as having the minecart dump on the same level - dwarves are not harmed if the items are dumped on them as long as the items don't fall. This does create the potential of a dwarf walking onto the tracks and isn't so great if you want to drop items 150 z levels.
If you really want to use a drop chute, then in some cases it's possible to build a "conveyor belt" which uses flowing water to move items, this only works well if the items weigh less than 100 units (99 is perfectly fine, 100 is a weird magic number where items become difficult to move by water), the main things which weigh more than 100 units are stones, some metal/stone items (especially furniture) and the corpses of large creatures. For reference, a heavy dwarf weighs more than 100 units, most dwarves weigh less.
How water pushing works is this: When water flows from one tile, into another tile, then the tile the water is flowing into becomes a "conveyor belt" which pushes items in the direction the water is flowing into the tile. This results in items being pushed from that tile into an adjacent tile even if the water itself isn't flowing into that tile.
Lets say you have a pump, followed by a floor, followed by a downstairs or grate which the water flows down, with a water return loop:
The water flow (seen from the side) like this:
pP↝↓
↑↜↜↜↜
Now, the forces tiles apply to items, looks like this:
pP∘⇉∘
↑↜↜↜↜
No motive force is applied to items in the pump outlet tile and items will just stay put there, this is because water isn't flowing into that tile from any direction [this is a logic bug, water is "teleported" into the pump outlet tile, so the game doesn't think water is flowing into the tile, and the game doesn't care what direction water flows out of a tile], now in the next tile, water is flowing into the tile from the left, so the tile becomes a "left to right" conveyor belt that will push any items into the tile to the right. This is in spite of the fact that the water is *actually* flowing downwards in that tile. Items end up deposited high and dry on the right tile.
Other than determining the fairly whacky logic of how water pushes items, I haven't really explored the potential of water conveyor belts. However they do at least have the potential to solve some otherwise intractable problems. For example if a drop chute drops items onto a water conveyor belt where the water is 4-6 tiles deep, then because of the water dwarves will be simply incapable of pathing onto the tile, the flowing water will push the items along until they end up on a dry tile where dwarves can collect the items. The only real proviso for this setup, is that items *must not* land on the pump outlet tile, as no motive force is generated in that tile. Also the water *must* be less than 7 deep at least some of the time, or again, the game wont generate any motive force.
Conveyor belts would be awesome, if not for the fairly serious limitation that they stop working well for items which weigh 100+. They do still work, but might take a few (dwarf) days or months to move all the items. It should also be noted that any such setup can double as a mist generator and dwarven water reactor.
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Topic: How to make a safe goods drop shute (pressure plate knowledge needed)? (Read 2255 times)