A Minecart Item Loader that can load 4 items at the time, sounds great doesn’t it? This was the first contraption of mine I’ve ever made a video about and posted it to YouTube and Reddit. And who knew, it got quite some views and people liked it!
So how does it work? When the Minecart comes in and hits the detector rail it gives off a redstone signal to a piston which then extends and pushes a glass pane against a block right behind the Minecart. Now that the Minecart can’t leave anymore it sits right on top of a powered rail leaning against the first hopper and a detector rail which continuously checks how full the Minecart is. Hopper two and three are to the left and to the right of the Minecart and the fourth hopper right on top of it, so we have hoppers on 4 sides pointing into the storage Minecart and filling it up with Items.
As soon as the comparator pointing away from the detector rail realises that the Minecart is completely filled with Items the Piston retracts and releases the Minecart from the machine. To change how full the Minecart has to be you simply change out the redstone dust and lever with a comparator and a chest pointing into the side of the first comparator and fill the chest with the desired amount for the Minecart to leave with.
If you wanna build this Item Loader yourself you should check out the updated and much smaller version of it which basically does the same thing but uses less resources and gets rid of some redundant parts.