[1.1.91] Extreme belt speed/splitter bug.

[xeneonic]

I was developing setups for BP's when I came across this issue. It involves 240/s belts and splitters. I used game.speed = 0.2 for visual clarity:


I tried to narrow down how it happens but instead only got more confused:




Some more troubleshooting with a belt counter mod:

Note the second time I grab stuff off of the belt, you can clearly see that the belts entering the splitter near the end of the "cycle" are suddenly not compressed anymore, the belt display counter also shows it and you can also see the compressed line behind the splitter entering the splitter at half the speed, further confirming it's not a visual glitch.

[sad_pancake]

Can you provide a save with these setups or at least mod list?
I tried similar design with 75/s seablock belts but they behave properly and I don't know which mods give higher speed belts.

Also it's a bit unclear for me: is the copper belt required and does the splitter has to have a filter set?

[xeneonic]

Sure: https://drive.google.com/file/d/1Evr-yY ... sp=sharing

When you load the map, the blueprint should automatically build; this part will help seeing the problem, as the issue will start appearing right away and was the most reliable way I could get the issue to visualize. And thus hopefully also easy to replicate and find a bug for.

As for the copper line... I should have been more clear. I am not sure how much it affects it but it seemed easier to replicate the bug when a filter was set and also had similar issues on the server I've been playing this on (Redmew Danger Ores, but they rotate maps/mods so can't say when it'll end and the next one will start)

But after I managed to get this bug to reliably trigger by simply pasting down the blueprint the way it does (Rotating it before putting down the BP will likely give different results, but didn't test), I suppose it's not needed to set a filter.

[sad_pancake]

From my testing the prio is irrelevant, also the same behaviour can be replicated with inserters.
The slowdown seems to happen way before the splitter. After removing some items from the left side of the splitter it compresses again before reaching the splitter.
It almost seems like a splitter suddenly slows down when the belt before is not fully compressed.

Screenshot from 2023-10-11 18-44-04.png (1.35 MiB) Viewed 754 times

Screenshot from 2023-10-11 18-46-25.png (1.34 MiB) Viewed 754 times

Edit: second screenshot is only couple ticks after first.
I don't know really how to make videos but I attach the savefile with minimum setup needed for reproduction.

Reproduction steps:
- Load the provided K2_bug savefile
- Remove some items from the belt by either pickup items on the ground hotkey or inserter.

I'd recommend to watch it tick by tick as it's easier to see the details.
Edit2: Also 120/s belts doesn't seem to have that issue.
Edit3: Attached wrong savefile.

[Stringweasel]

Maybe each transport belt lane of the splitter can do a maximum of 60 items per second, in some conditions?

[sad_pancake]

It could be some kind of tick limitation, I don't know much details about how splitters work.

However playing around with it a bit more. I found out that modifying splitter by either:
- adding and removing a tile of belt to the bottom lane (either input or output)
- rotating the splitter
fixes the issue for a bit. (Changes done when time stopped)

Screenshot from 2023-10-11 23-14-20.png (585.9 KiB) Viewed 652 times

Then it comes back somehow by itself.