A bit more tidying up, addition of a hopper and chute to load Legos into the drum, some fine tuning of the angles and software and it's done!

It's not perfect but it is really fun to watch. The main remaining issue is that the scoops inside the drum sometimes pick up quite a few pieces, which then overwhelm the vibe feeder and they end up tailgating each other past the sensor. Something to tweak later. I'd also like to add a touchscreen with start/stop buttons and some readouts of brick counts, speeds, etc. Other ideas in the comments please!