What's up with inserters?

[evilbrain]

Here are my assumptions:
1. Each belt tile has 32 slots.
2. Each item occupies 9 slots on a belt.
3. Yellow belt advances by 1 slot every frame.
4. If there are no items on a belt inserters will always place an items on the same slot of the belt.
5. If the usual slot is occupied inserters have two options:
a) Wait for a free slot
b) Drop an item to nearest slot available before or after the item occupying the default slot if a free slot is close enough (don't know how close it needs to be)
6. In both these cases they will not leave gaps between items on a belt and will not break belt compression.
7. If there are less than 9 free slots between 2 items on a belt inserters consider these slots occupied and skip them.
8. Hand rotation times are always the same if inserter takes items from a container (like a furnace)

Example 1: 2 inserters unload 2 items on a belt at the same time. First item occupies slots 0-8 (9 total), second item occupies slots 32-40 (9 total), slots 9-31 (23 total) are free. This gap can contain 2 additional items, occupying 18 slots, leaving belt with 5 unoccupied slots that cannot be filled. This section of the belt cannot be compressed no matter where items will be dropped.

Example 2: same as 1, but second inserter skips 5 frames after the first inserter. Now first item occupies slots 5-13, second item still occupies slots slots 32-40 and slots 14-31 (18 total) are free. These 18 slots can be filled with 2 items without any gaps. This section of the belt can be fully compressed if items will be dropped into right slots.

Now imagine a belt as a constantly moving line of slots numbered from 0 to 8. If inserters drop items only on slots marked 0 this will ensure that number of free slots between items on a belt are always divisible by 9 and this belt can always be fully compressed. This can be achieved by circuit network signal cycling from 0 to 8. If there is an item on a belt inserter will wait for a free slot or drop it next to the existing item (see assumptions 5 and 6). Because 2 tiles are 32 slots apart there will always be a delay of 5 frames per tile the further you go down the line. Therefore:
Delay = Tile_Number * 5 mod 9. This pattern will repeat every 9 tiles. So the magic delay timings should be: 0, 5, 1, 6, 2, 7, 3, 8, 4. And since rotation times are supposed to be the same (assumption 8) everything should sync perfectly.

I made the circuit. It doesn't work. At least 1 gap every 12 items.

What can be happening - hand rotation times are not the same (doesn't seem to be the case), or inserters are able to misplace items on belts or inserters can move items that are already on the belt.

So what's up with inserters?

[Yoyobuae]

What you explain does work, but you'll need to be wary of a number of things:

• Chunk boundaries. Press Shift+Space, notice the darker grid divisions, those are the chunk boundaries. Circuits spanning across chunk boundaries have an extra tick delay under some circumstances. I just try to avoid or minimize crossing said boundaries to in my circuits to be safe.
• Inserters pointing north take a tick longer moving item from chest to belt than ones pointing in other directions
• Delays across belt corners, side loaded belts, splitters are kinda weird. The time an item goes thru takes 1 tick longer the first time thru than the remaining times. Almost as if the item "remembers" having gone thru before.
• Time to pickup from belt is a bit less predictable, depends on item position.
• Inserter stack bonus messes things up big time.

Circuit network allows ultimate precision control, but the game was not designed for that. So you'll run into more and more of this kind of problems as you try to go more and more precise.

[evilbrain]

Did this with Creative Mode mod.

No stack bonuses. No belt corners. All inserters face the same direction. All inserters rotate counterclockwise to unload. Everything is inside one chunk. They pick up from containers so the pickup is instant if there is an item present (with this settings they can't even grab from belts).

[evilbrain]

The time an item goes thru takes 1 tick longer the first time thru than the remaining times. Almost as if the item "remembers" having gone thru before.

Spiltters remember belt side for each item type that passes through.
https://www.youtube.com/watch?v=FQGFhebyrSI

[vtx]

That's why underground belt are usefull for compression it'll fill the gap that otherwise you could not normally place items.

[impetus maximus]

That's why underground belt are usefull for compression it'll fill the gap that otherwise you could not normally place items.

what vtx means is place an underground belt where the inserter places an object on the belt.
it take priority over items already on the belt. very useful for placing copper/iron plate and getting full compression.

underground.png (782.75 KiB) Viewed 3294 times

[Syrchalis]

I didn't want to open a seperate thread and since it's inserter related I thought I would ask this here: I recently noticed that normal inserters (which I love to use) can't pick up items from a blue belt. Is this a bug or intended? If the latter, why?

[impetus maximus]

I didn't want to open a seperate thread and since it's inserter related I thought I would ask this here: I recently noticed that normal inserters (which I love to use) can't pick up items from a blue belt. Is this a bug or intended? If the latter, why?

not a bug. they are too slow for blue belts. also, burner inserters can only reliably pick up from a straight yellow belt (not on bends)
again too slow for red belts.