I tested DaveMcW's unloader, it does indeed unload nearly compressed 4 blue belts per wagon.disentius wrote: @zOldBulldog: DaveMcW's is brilliant, and the most efficient for 4 belts per wagon
Trivial issue: The center chest (the one that goes from chest to chest to chest before being emptied by the 2 inserters into the belts) tends to empty faster than the rest, occasionally causing minimal interruptions (thus the 4 belts per wagon don't fully saturate). Even so, it is very close and good enough for me. IMHO an improved version would only be worth it if it remains about as compact as it is now, full saturation is probably not worth it if it requires a much larger footprint.
NOTE/EDIT: It requires an 8x8 balancer, or uneven ore consumption will eventually cause some wagons to empty faster while leaving others nearly full and thus causing trains to take much longer to unload... defeating the goal of fast unloads.
EDIT 2:. I found reports that even lane balancers are only a temporary solution. Eventually one of the chests would still empty and hold up the whole train. Circuit logic unload can help but it kills throughput. I have not found a good complete solution that preserves unload speed.
For those who need a way to supply trains fast enough, below is a screenshot. The blueprint and usage description is at factorioprints: https://factorioprints.com/view/-LCyNqfc04vWxjS8v8DG