Comment by jacquesm

Yes, that's roughly the gist of it. This is a hard problem because Lego comes in many shapes and sizes, a pre-sieving step limits the pieces that hit the belt at 42 mm largest cross section. So anything below that (but possibly much longer than that, all the way up to 2x1x16) can be found in the hopper.

There are some really good suggestions in this thread, the one that stands out for me most is the brush edged screw feeder, I think that one has most properties just right to work.