Avezo wrote:I'm interested both in double headed trains and single-headed and how big they need to be to run over behemoths freely.
There is no train size that can run over a behemoth that I know of. The first behemoth is killed but stops the train allowing it to get mobbed. After that the train is unable to accelerate and gets destroyed. At least that's been my experience. Extremely happy to be proven wrong, anyone?
As for train lengths, it sounds like you are driving trains into contested areas with biters around. Have you considered the new artillery wagon? It can push back the spawners from near your outposts. Warning: artillery wagons are very heavy, one artillery = 4 cargo or A=CCCC
So these two trains: LL-CCCC and LL-A will be the same speed. If you are running optimum trains as calculated by
Frightning as 6 L and 13 C you could build them out as:
LLLLLL-CCCCCCCCCA
That's 6 Locos pulling 9 cargo + 1 artillery for a total cargo weight of 13, total train weight is 12+13=25.
You can also consider how fast your miners are and how distant your outposts are. One mining drill gets ore at a rate of 0.525/s. On a big ore patch, say 10x10 drills you have 100 drills and get ore at 52.5/s but you probably have some
mining productivity research done, maybe level 15 for a 30% bonus. All up 68.25 ore/s without speed modules. A single cargo wagon can hold 4000 ore. So it takes 100 miners with level 15 research 4000/68.25 = 58.6 seconds to mine enough to fill one cargo wagon. Basically 1 minute per wagon. So if your roundtrip from outpost to smelter and back again, including load/unload times, is 6 minutes (1 min load, 2 min drive, 1 min unload, 2 min drive back) then a train with 6 cargo wagons would be a good fit.
A fully upgraded stack inserter moves 744 items/min. If you use 6 per cargo wagon that's 4464/min or 54 seconds to load or unload 4000 ore. It is possible to use 12 stack inserters per wagon and cut that time in half.
How far does a train travel in 1 minute? Top speed of rocket fuel trains is 298.1 km/h so with starting/stopping, traffic etc maybe they average 120 km/h. That's 2km in 1 minute, 2000 tiles or 62.5 chunks in Factorio terms. For reference a radar shows an area of 7x7 chunks.
My ore patches are usually not big enough to fit 100 miners and they are usually not a 2 minute drive away - so I use smaller trains.