Inserter/Assembler match and logic... using copper coil as example

[zOldBulldog]

I have been playing for ages and I must confess that I still don't fully understand the proper way to calculate what is the right inserter (or number of inserters) for a particular assembler and formula.

And by looking at the many designs that use copper wire (like Green Circuits) it is quite clear that I am not alone, as I see designs using 1 to 3 fast or stack inserters, all for the same formula and assembler.

So, assuming a blue assembler and the copper wire formula, could someone please walk through the calculations, ending on a choice of inserter type and how many?

I started by collecting some basic info:

Copper wire info:
- 1 copper plate ==> 2 copper wire
- Production time: 0.5 s (not sure in which assembler type)

Assembler crafting speeds (not sure in what units):
- Grey Assembler = 0.5
- Blue Assembler = 0.75
- Green Assembler = 1.25

Inserters (no bonus / bonus 7):
(Is this items/second?)
(Assuming chest-chest speed, will be slower on belts)
- Yellow = 0.83 / 2.5
- Red = 1.15 / 3.46
- Blue/Purple = 2.31 / 6.92
- Green/White = 2.31 / 27.69

My guess (probably wrong) would be:
- generic calculation: 2 wire/ half second = 4 wires per second.
- 4 wires per second * 0.75 (blue assembler) = 3 wires per second.
- 1.5 copper plate per second.
=> Input: 1 blue/purple/green/white
=> Output: 2 blues/green with no bonus. 1 might do, depending on how much stack bonus.

And this is where I get lost... I see many designs with more inserters, up to 3 green. So I either got these numbers wrong, or a lot of people are using excess inserters because they don't understand the math and want to be safe.

[Koub]

The inserter topic is very complicated if you want to optimize it.
https://wiki.factorio.com/Inserters
My general rule of thumb :
- if the assembling machines are input starved, add moar boosters inserters on input
- if the assembling machines are output limited, add more inserters on output
- if the inserters take from/to belt, mixing stack/fast inserters (with stack override 1) optimizes both latency and throughput
- is transfering from container to assembling machine (and vice versa), then stack inserters are optimal for throughput, but fast can be enough on slower/less item-heavy recipes.

[zOldBulldog]

The inserter topic is very complicated if you want to optimize it.
https://wiki.factorio.com/Inserters
My general rule of thumb :
- if the assembling machines are input starved, add moar boosters inserters on input
- if the assembling machines are output limited, add more inserters on output
- if the inserters take from/to belt, mixing stack/fast inserters (with stack override 1) optimizes both latency and throughput
- is transfering from container to assembling machine (and vice versa), then stack inserters are optimal for throughput, but fast can be enough on slower/less item-heavy recipes.

LOL. I was looking at that very same link to get the numbers on the OP. Not that I could understand much of it.

Looks like I was already using your method before this post. It just felt like I wasn't doing things the "Factorio way"

I assumed my basic calculations were right and I figured I'd try for the copper cable:
* red-belt => 1 blue inserter => blue assembler => 2 blue inserters => red belt
* the above x 20
* 1 copper belt in
* 2 copper wire belts out
(and before I get yelled at... this is very local, all of the wired being consumed when under full demand load)

I use Bottleneck, so my plan was to watch for red/yellow dots once I manage to put it under full demand.

But it sure would be nice to actually understand the math so that I could "do it right"

[Serenity]

You can also just open the assembly machine interface and watch the ingredients in there. You'll see when they are waiting for input

This works for example (green circuits, 8 beacons):

[Bauer]

Obvoiusly, the problem is not the calculation of items you have to move per second.

The problem is that the transfer rate of inserters to and from belts vary a lot depending on the filling status of the belt. As a result, you need more/faster inserters for ingrediants as the belt gets empty and more (faster doesn't help) inserters for products if the belt is nearly full.

Output side:
This is the easier problem. Do the calculation of items/s you have to move and chose the right type and number of inserters with the help of the table in the wiki. The last assembler outputting stuff on that belt side/lane gets one more inserter.

Input side:
No wiki table will help you here. The easiest way indeed is trail-and-error as others have already suggested.
Very often, the problem is that the inserter(s) are idleing because the assembler still has stuff. A few ticks later, when stuff is needed, the items do not come quickly enough on the belt (or the inserter has to move from lane to lane). Thus, the inserter throughput is far from the figures in the wiki. Instead of adding more inserters (that potentially suffer from the same problem at the same time), adding a buffer-chest limited to one or two stacks can improve the throughput a lot. In this case, you have 2 inserters, one into the chest and one chest-to-assembler. For extreme cases, you can also use two inserters into the chest (underground-inserter-chest-inserter-underground).

[mrvn]

Also consider:

1) while a stack inserter can move 12 items an assembler might not produce 12 copper cables before it stops. You might not get full throughput. But at least I think the inserter doesn't wait if more items will appear soon.
2) An inserter will only start getting stuff when the target assembler is low. It then takes time to grab items and rotate. The assembler can run out in that time.
3) Inserter speed changes over time as you get bonuses. So without bonus you need fast inserters for the copper wires but with the inserter bonus yellow suddenly work too.