delicate orbit
In our SE playthrough, we notice that even though are liquid requests seem filled, we still sometimes receive an additional (or more) train. Because the storage tanks are already full, the train is not able to empty its cargo before the two minute timeout is reached. This causes the train to return to the depot with its contents. In the pictures are our wiring setup and the combinator settings. Do you have any idea what could cause this problem?
clear wasp
What do the requesters look like?
delicate orbit
I'm not sure what you mean with the requesters. The first pic shows the combinator in question with the requests in the second one
clear wasp
Ah, figured that was the provider station, given that it has a provider threshold
delicate orbit
Yeah that is sort of a safety switch so trains don't go there to load liquids
clear wasp
Right... Set a requester threshold too, and a provider threshold on the provider, matching the capacity of your trains
Right now I'll guess it dispatches a bunch of trains for a tiny load, they get filled completely because loading does not respect the requests, and the requester station overflows
delicate orbit
that makes sense
i'll give it a shot
i figured the train size itself would sort that
like this then? my trains are only 1 wagon
clear wasp
Yes, though that will give issues with the current request size
You're requesting up to half a wagon and demanding it not send a train until it needs a full wagon
Easiest solution is to increase the request, but you could also lower the threshold and change your provider stations so they stop loading the train once it has what it requests
delicate orbit
we only let trains ride when they can bring a full load to reduce unnecessary traffic
just to make sure I understand correctly: that -10k means the train requests a 10k load? I've always assumed it meant that that was the threshold for when a train gets sent
clear wasp
Yes, that's the maximum amount of material you want at the station
You then subtract however much is already at the station to get the actual request (or well, add to the negative number, really)
Say the request is set to -10k, and the station has (+)6k, LTN will see a demand for 4k items. If that is above the request threshold, it will try to send a train carrying 4k items
delicate orbit
right, that I understand. and we have set a provide threshold of a full train so circumvent the half full train problem
clear wasp
Yup
Though if you only have a provide threshold, but no requset threshold, LTN may still send a train for a small amount of items
It simply sees that the requester wants that small number of items, and that the provider is capable of providing it
delicate orbit
Could it send another one in the time the first one is on the way because the request isn't filled yet?
clear wasp
Yes
delicate orbit
Could it send another one in the time the first one is on the way because the re...
This would be a universal problem if that was the case?
Then there would be a continuous request for trains until the request was filled
clear wasp
Eh, I think something got lost along the way
A train that is currently on the way to the station will effectively have its expected cargo added to the inventory of the requester and subtracted from the inventory of the provider if it hasn't gotten there yet
delicate orbit
So far so good
clear wasp
So if LTN sends a train to a provider to pick up 10k items, and that provider has 15k in storage, LTN will treat that provider as if it has 5k items as soon as the train is dispatched
Effectively, that stops it from sending too many trains
If a requester is drained of items fast enough though, LTN can definitely have multiple trains on the way at once
And to finish that thought: if those trains are all carrying way more than LTN is expecting them to (due to missing requester thresholds), it can easily overflow the requester
delicate orbit
I think I'm still with you
but how do request thresholds fix that?
I don't get how the fluid threshold and the request threshold connect to each other
clear wasp
They force LTN to wait until the requester has space to unload a full train, at which point it will simply send a full train because that's how much the station is missing
Space in its request value that is, not space in its storage buffer. That's your responsibility
Request threshold basically is how many items the station needs to be missing from the request value before a train is sent
So if the request is 10k and the threshold is 6k, LTN will only send a train once there are 4k items left (6k below the request)
delicate orbit
Would just setting a fluid request and request threshold of 25k be a simple solution?
clear wasp
Then it will only send a train once the station is completely dry
delicate orbit
We have 2 storage tanks as a station
clear wasp
You'll want some difference between the request and threshold to make sure the station can keep running while a train is coming
With 2 tanks you could set the request to -40k
Or anything up to -50k, really
delicate orbit
With 2 tanks you could set the request to -40k
and the assumption here is then that you don't use 10k fluids while the train is on its way?
so you dont run dry
clear wasp
15k even, yes
Once you reach 15k fluid left, it will send a train to get the station back up to the request value, for which it needs 25k or a full train
delicate orbit
We talked it through and we think we almost get it
We now understand why the request was overfilled, but how come we then got several trains? There have been situations where two trains were sent, the first train couldn't even empty its cargo, so the second train had no chance at all
delicate orbit
If a requester is drained of items fast enough though, LTN can definitely have m...
And I dont think the throughput was high enough for this to be the case
clear wasp
If there is no threshold it can send a train for whatever the global minimum is, usually a few k
So as soon as the requester is missing more than that, a train is sent
delicate orbit
Assuming another provide threshold is met then?
clear wasp
Yes, assuming the providers are completely filled
you can also have the inverse scenario when you have set only request thresholds and your providers are running low. The outcome is the same: LTN will send a train to pick up a tiny load as soon as the provider has more items than the global provide threshold
That's why you need both provide and request thresholds
delicate orbit
maybe the tl;dr is we were lazy
clear wasp
lol
delicate orbit
the reason why we didnt run into trouble with items is because we have warehouses there, so the cap was almost never reached
it fits
..in more ways than one
clear wasp
lol
Ideally you'd set thresholds everywhere, limit loading to whatever the train requests (including item type) and use filter inserters for unloading
That way your setup should be pretty foolproof
delicate orbit
we're gonna retroactively add request thresholds everywhere
which brings me to another question: how does that work with stations which have both items and fluids?
delicate orbit
we're in too deep for that
does either stack or count threshold overrule the other?
clear wasp
I'm not sure tbh
delicate orbit
Would you mind talking us through one example to drive it home?
delicate orbit
of a provide/request scenario
clear wasp
How about this graphic from the LTN manual?
May have to open that in browser, it's kinda horrible, lol
To make some things clear there: the requester has a request of 128k and a request threshold of 15k, the provider has a provide threshold of 15k
delicate orbit
Maybe it will make sense with what you told us because it was always difficult
clear wasp
The vertical blue and orange bars show a bunch of possible inventories for both of the stations, and the arrows between them show what happens for each of the combinations of the two
delicate orbit
it does make more sense now
From what it seems, stack threshold seems to > count threshold
clear wasp
Even if the number of items it sets is lower?
