My impression is that the fastest/easiest way to do it would be putting all the pieces inside hopper with the selector at the bottom. Perhaps using compressed air to push the falling pieces into different containers as they fall. I believe there’s already something like that in produce factories, separating vegetables by state/size.
I interviewed once with a company that made rice and grain sorters. They have a massive hopper at the top and pass the grain in a curtain through a machine vision camera, and then decide in real time where each grain goes based on the image.
Apparently pretty much every grain of rice you've eaten has been through a machine like that.
I don't know why this can't just be a cleverly laid out arrangement of layered sieves, each one parsing a different object .. I don't see how it needs to be mechanical in any sense other than "pour in the lego junk, out it comes neatly sorted", a la coin-sorting machines ..
I could see people wanting to add on color detection for the bricks, but even that could still be solved by camera + servos/steppers and a chute that goes to different bins. No need for an arm.
It is probably possible to do it, but the sieves would be quite big, just to account for the very large number of pieces, as well as having to “orientate” them correctly using only gravity.
