How to unload 6 blue belts per train wagon
I spent my saturday trying to improve the commonly accepted design limit of 4 blue belts per train wagon. First I did some benchmarks regarding for what percentage of time a 2-4 train is actually unloading (assuming full throughput) and for how long it is departing or arriving.
Apparently the train is spending 77.0 % of the time unloading, let's call it the unloading efficiency. Now, what is the maximum sustained throughput we can get? 12 fully bonused stack inserters take about 12 seconds to empty a wagon with 4000 plates and with an unloading efficiency of 77% we get:
Throughput from wagon to chests T_c = 0.77 efficiency * 4000 plates / (12 seconds * 12 inserters) ~= 21.4 plates per inserter per second
Noting that this is more than half a blue belt (20 items per second), it is possible to unload 12 chests into 6 blue belts. The problem is that it takes 3 stack inserters to physically fill a blue belt. So from each 2 chests we want 1 blue belt but at least 3 stack inserters. So at some point there needs to be a chest that is unloaded by more than one stack inserter. The challenge turned out to be how to do that compactly.
TLDR: 6 blue belts per wagon is possible but we need lots more chests and inserters.
My designs
The first design achieves 3 blue belts from one side of a train wagon, with 4 consecutive train wagons. This means a total of 2*3*4 = 24 blue belts from one 2-4 train. Screenshot Blueprint
My second design is a bit more compact but only achieves something like 2.5 blue belts on the middle two wagon sides. Screenshot Blueprint
Posted Dec 8, 2018, 8:25 PM UTC
Using cars (or tanks) rather than chests may make it easier to increase the number of stack inserters unloading onto belts.
Using wagons (tanks would work the same way) you are limited to how fast you can cycle trains.
This layout approaches 9.4 belts per wagon (accounting for train cycling it can pass 8):
!blueprint
Blueprint Image
Very nice, especially in 0.17 when bots should be able to place wagons etc.
Yes, I did briefly experiment with them but ended up deciding against it as vehicles can't (yet) be blueprinted.