Minecraft wiki entry for Storage_minecarts, associated text: Design C is a tileable unloader. Larger than design A, but it can hold minecarts with a closed fence gate to prevent them from bouncing off. This design requires that the minecart enters the unloader fast enough to get up onto the detector rail, otherwise it will get stuck on the unpowered powered rail. A single active powered rail two blocks before the powered rail over the hopper is enough to guarantee correct entry.