Design A is probably the simplest. When the hopper has at least one item, it deactivates the Powered Rail so a storage cart coming from right will be stopped under the hopper. After feeding the cart with all the items in the hopper, the powered rail gets reactivated so the cart starts going right. A possible downside of this design is that the powered rail is always active as long as the hopper is empty so if a cart comes to the empty loader it immediately bounces off to the opposite direction. This might lead to an inefficiency of the system if there is a great distance between the loader and unloader.
Earliest Known Publication: 28 March 2013
Design A' is a variant of design A to make it flat.
Design B is a combination of a hopper and a falling edge detector. It activates the powered rail for 4 redstone ticks only at the moment when the hopper becomes empty, so a cart will stop there until you put some items into the hopper and all of those items are transferred to the cart.
For all the designs shown above, minecart with chest will be stuck at these loaders when the cart has no space to receive items from loaders.
Design C has an advantage that, minecarts with chest will not get stuck as long as they are empty while entering the loader. This design has two operational modes: when the loader doesn't have a cart, a small chest that serves as a "buffer" will accumulate items from the large chest above. And when it has a cart, items in the buffer will be transferred to the cart and nothing more. It has a T Flip-Flop that switches between two modes, connected to a detector rail.
Earliest Known Publication: 5 May 2013
The minecart is stopped by the Powered Rail on an incline and the Hopper above. You will need 4 powered rails to get the minecart up the hill enough to be on the Detector Rail properly. The minecart will rest on the Detector Rail so the Comparator in subtract mode can see how full it is. You can fill a container (I show a Hopper because it needs fewer items per signal strength) to a certain level and have a Comparator send that signal into the side of the first Comparator to power the Powered Rail and send the minecart on its way.
If your signal strength is higher than the amount of items your minecart can hold, it will be stuck until someone can move some items around. (Your signal is for full stacks, but you fill the cart with half stacks)
Design E is "stable" and the Minecart with Chest will leave until it's full. The reason I use "stable" here is the Minecart with Chest will keep running between the golden blocks while loading. The Detector Rail between the golden blocks can detect how full the Minecart with Chest is. Once it's full the "door of gold" will open. All Powered Rail showed here is powered from side.
Design A is probably the simplest. As soon as the hopper receives at least one item from a cart arrived above, it deactivates the Powered Rail so the storage cart came from left will be stopped on top of the hopper. After taking all the items in the cart, the powered rail gets reactivated so the cart starts going left. A possible downside of this design is that the powered rail is always active as long as the hopper is empty so if a cart approaches to the unloader too fast, there is a non-negligible chance that the cart bounces off before getting braked by the deactivated powered rail.
Earliest Known Publication: 28 March 2013
Design A' is a tileable variant of design A.
Design B is a variant of design A: It has a detector rail which temporarily deactivates the powered rail to prevent carts from bouncing off.
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.
For all designs shown above, minecart with chest will be stuck at these unloaders when they have no space to receive items from carts.
- InventorTester (28 March 2013). "Extremley Compact Minecart loader/unloader". Minecraft Forum.
- koan911 (5 May 2013). "Detect when chest-minecart is full and launch it?". Minecraft Forum.