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how to make builder train

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how to make builder train

Posted: Mon Dec 22, 2025 4:09 am
by spesest
Hello everyone on the Factorio forum,
I'm thrilled to have discovered this site and joined.

I'm a Factorio beginner who's been playing solo and enjoying it in solitude, with only about 500 hours of playtime so far.

I'm currently designing a modular factory using LTN mod trains.

I have a question for you all regarding factory expansion. (I'm not sure if this is the right board for such questions)

I plan to operate a builder train.

I'll lay outer train tracks and first build a construction site station myself.
I want to implement a system where I place the necessary blueprints for that module into the signal, and the signal sends the required items to the Builder Train station at the constructed mall.
Then, using logistics robots, the items produced at the mall are loaded onto the train in the required quantities. The train operates to the Construction Site station based on appropriate quantities or timing.
I also want to prioritize the transport of items.
First, Phase 1 involves transporting RoboPorts, utility poles, construction robots, railways, etc., to complete the internal railway and RoboPort system for construction.
Phase 2 adds conveyor belts, feeders, etc.
Phase 3 introduces factories and train stations to begin operations.
Phase 4 transports additional items like floor concrete or modules.


How can I find explanations or methods that satisfy the requirements outlined above?

I will listen attentively to your valuable insights.

Re: how to make builder train

Posted: Mon Dec 22, 2025 8:42 am
by mmmPI
Do you WANT to use LTN for this ? or are you saying it to provide a detailed picture of the situation when asking for "any" solution ?

Have you tried anything already ? Are you familiar with combinators ? what scale do you plan to use this for ? if you have a couple pictures of the current factory that could illustrate which methods would be the most appropriate for the scale.
spesest wrote: Mon Dec 22, 2025 4:09 am I want to implement a system where I place the necessary blueprints for that module into the signal, and the signal sends the required items to the Builder Train station at the constructed mall.
This in particular goes a little beyond what you can automate in factorio without mods , if you are not willing to manually input in a constant combinator what is required for a blueprint, there will be no way for you to interact with the precise list of components for such trains system, i believe even with LTN, ( albeit i'm not familiar with recent updates) i think you'd still need additionnal mod to read the blueprint component.

A comonly used approached without mods , instead is to have a fix list using 1 or 2 logistic group, one called "defense train loadout" and another one called "outpost defense supply". In the first one you setup everything you want the train to carry, and in the second what every defense outpost unload area should be receiving as supply.

This means that you don't have the train carry 63 mining drills and 189 modules and 256 belts because that's the precise number on the blueprint, rather a fix quantity say 50 150 300, and the train takes 1 or 2 or 3 trips to "build" the thing ( or supply the defense outpost ). The logic for builder train and defense train is similar because a defense train carryies roboport, repair packs walls turrets ammunition and so on. You can adapt this to have a train that carries chemical plants and assembly machines and beacons or "anything" you set up on the list. ( You "can" use LTN to manage those trains as if they were supplying ore or circuits ).

If you want to automate further, you can create an unloading station blueprint, ( the construction site to place manually or using the outer train track ) this one should roughly contain at least 1 inserter unloading things from trains into a logistic chest, and from this chest another inserter filtered to only pick up bots, and place them in an adjacent roboport. You can connect this second inserter with wire to the roboport in which the robots are inserted to limit the number of construction and logistic bot to a predefined amount. This particular part is what would transform a regular unloading station into either a defense outpost, or a construction site, depending on which item are made available to that newly created logistic network.

Example of this you can find thus under the name "defense train" or "supply outpost" , even if you are after a "builder train" there exist plenty example, i can post a minimalist one if you're interested. But if you want to use LTN to transfer the precise quantity only, which is a little bit different , then i don't have such things ready with all the steps, and i can't think of one example, again maybe with additionnal mod like recursive blueprint

For the different phase of construction, the less "combinator heavy" approach i believe is just to use several trains, the recursive blueprint mod typically offers lots of possibilities for this by allowing to place down successive tiers of blueprint, but that require more combinators work to get going.

(also welcome to the forum, this post appears to be in the right board, you can also read/ask in the LTN more specific area viewforum.php?f=214 :) for recursive blueprint and the staged construction phase, i think it's easier to find information on videos )

Re: how to make builder train

Posted: Mon Dec 22, 2025 12:16 pm
by Tertius
spesest wrote: Mon Dec 22, 2025 4:09 am I want to implement a system where I place the necessary blueprints for that module into the signal, and the signal sends the required items to the Builder Train station at the constructed mall.
Then, using logistics robots, the items produced at the mall are loaded onto the train in the required quantities. The train operates to the Construction Site station based on appropriate quantities or timing.
The game has no means to send construction requests into the circuit network, so you never know how much is actually required to build all ghosts within the reach of some given logistic network. This information isn't available at all, not even with mods.
You know of course how much some given blueprint wants and code this into a logistic group and provide this with a constant combinator, but as soon as you change that blueprint, you have to update the logistic group as well. To collect every material required and send a single train with everything is very static and error prone - it might happen you change something on the construction site, or it can happen not all material is available and much more.

Instead, I recommend you design a universal construction train that carries a little of everything required to build your outposts in general. Like a travelling salesman. One stack of this, 2 stacks of that, and so on. The train item stock is the same for every train and not dynamic. As soon as the train arrives at the construction site, it unloads a little bit of everything, which is then used for satisfying construction requests from the ghosts. The train returns to the baseif some item gets exhausted and returns restocked to continue construction. If everything is finished, you can remove the construction item requests and either the construction station as well, or just keep requests for maintenance such as wall replacements, repair kits, ammo. The obsoleted items can be carried back to the base by the supply train if you include some garbaga collection circuit and wagon.

I strongly recommend you don't start to use LTN. LTN is an obsolete design and an obsolete approach to trains. It was made for game version 1.0 where no train limits existed. It's obsolete as of game version 1.1, namely the train limit feature. It's even more obsolete with the interrupt tech from game version 2. Don't center your thinking into a "provider - requester" pair. Instead, think about "I have an empty train, let's send it to a station that will load items" and "I have a full train with items, let's send it to a station where these items are wanted". For the latter, you never need something like LTN.

Your additional phases 2..4 aren't relevant for this approach. Everything that can be constructed will eventually be constructed with my approach. Construction just spreads along with roboports being constructed eventually and proper power supply. The only thing you have to provide manually is a working station and one roboport. Not even bots in the roboport, if the station is able to put unloaded robots into the roboport until the wanted amount of robots is deployed.

It' also not necessary to send any kind of item set from the construction site to the main base, because the train will always carry a static set of items. This enables parallel construction of multiple sites, because all trains can be used for all construction sites.

tl;dr
My approach to your task is like this:
- have a construction train at the base being filled with an assortment of items at the base station, items defined in a logistic group for loading
- have construction site station that opens up if it wants the items of the construction train.
- if the construction train arrives at the construction site, it unloads a set of items, items defined in a logistic group for unloading
- construction takes place with the unloaded items, so the unloaded items are removed from the station stock
- train returns with new supply as long as there are still items to unload to refill the stock
- if there are surplus items at the construction site, for example deconstructed wood and stone, this is being carried back by the construction train.

I designed (over the years) a blueprint for an appropriate loading station, for an appropriate unloading station, and an interrupt controlled schedule for the 4 wagon train. All vanilla. So it's possible with vanilla, no LTN, and it's working perfectly in my opinion.

Re: how to make builder train

Posted: Mon Dec 22, 2025 10:56 pm
by spesest
Thank you for your detailed response.

My precise intention involves using ltn to operate trains while transmitting signals via the constant combination unit to sequentially deliver the required quantities of materials from the mall to the construction site. Upon completion of construction, the remaining items (including any excess deliveries and materials like wood and stone) are retrieved and returned to the mall's recycling station. This encompasses the entire process.
mmmPI wrote: Mon Dec 22, 2025 8:42 am
This in particular goes a little beyond what you can automate in factorio without mods , if you are not willing to manually input in a constant combinator what is required for a blueprint, there will be no way for you to interact with the precise list of components for such trains system, i believe even with LTN, ( albeit i'm not familiar with recent updates) i think you'd still need additionnal mod to read the blueprint component.
I'm not sure when it started, but it seems there was an update where you can now place the blueprint itself into the constant combinator, and clicking it automatically inputs the required logistics lists. I have modular blueprints for my factory. I want to build a construction site area in one corner of the module and establish a system where, after simply pasting the blueprints for Constant Combiner and put a roboport, the mall automatically delivers the required item lists sequentially and recovers leftover materials or waste after construction.

I believe it should be possible to build a system where the logistics list input into the constant mixer sends a signal to the request box in the mall. This system would then prioritize delivering specific items based on the sequence previously set through other mixers or similar devices. Only after the delivery of those items is complete would the next item be shipped. (The construction site might also need a circuit to track items dropped by the inserter.)

I'm contemplating this specific circuit network or method. While it feels feasible, building the concrete system doesn't seem easy, so I'm requesting assistance.

Re: how to make builder train

Posted: Mon Dec 22, 2025 11:06 pm
by spesest
Tertius wrote: Mon Dec 22, 2025 12:16 pm
I strongly recommend you don't start to use LTN. LTN is an obsolete design and an obsolete approach to trains. It was made for game version 1.0 where no train limits existed. It's obsolete as of game version 1.1, namely the train limit feature. It's even more obsolete with the interrupt tech from game version 2. Don't center your thinking into a "provider - requester" pair. Instead, think about "I have an empty train, let's send it to a station that will load items" and "I have a full train with items, let's send it to a station where these items are wanted". For the latter, you never need something like LTN.

Your additional phases 2..4 aren't relevant for this approach. Everything that can be constructed will eventually be constructed with my approach. Construction just spreads along with roboports being constructed eventually and proper power supply. The only thing you have to provide manually is a working station and one roboport. Not even bots in the roboport, if the station is able to put unloaded robots into the roboport until the wanted amount of robots is deployed.

It' also not necessary to send any kind of item set from the construction site to the main base, because the train will always carry a static set of items. This enables parallel construction of multiple sites, because all trains can be used for all construction sites.

tl;dr
My approach to your task is like this:
- have a construction train at the base being filled with an assortment of items at the base station, items defined in a logistic group for loading
- have construction site station that opens up if it wants the items of the construction train.
- if the construction train arrives at the construction site, it unloads a set of items, items defined in a logistic group for unloading
- construction takes place with the unloaded items, so the unloaded items are removed from the station stock
- train returns with new supply as long as there are still items to unload to refill the stock
- if there are surplus items at the construction site, for example deconstructed wood and stone, this is being carried back by the construction train.

I designed (over the years) a blueprint for an appropriate loading station, for an appropriate unloading station, and an interrupt controlled schedule for the 4 wagon train. All vanilla. So it's possible with vanilla, no LTN, and it's working perfectly in my opinion.
ltn will serve as one means to deliver these needs. I also tried using the interrupt system in vanilla, but seeing the state where goods remained loaded onto the train persistently, I wasn't quite sure how to resolve it.

My intention is not to preload all necessary items for each module onto the train in an oversupply state.
Some modules, like the reactor, contain items that aren't needed in very large quantities. Components like concrete or factory parts within each module are secondary items. Once produced, they can be shipped separately and installed later, so sequential installation is being considered.

The next video will cover my intentions to some extent.
https://youtu.be/UAebxuokkyM?si=fnA_zE5xKH9tDbxt

Re: how to make builder train

Posted: Tue Dec 23, 2025 12:11 am
by mmmPI
spesest wrote: Mon Dec 22, 2025 10:56 pm I'm not sure when it started, but it seems there was an update where you can now place the blueprint itself into the constant combinator, and clicking it automatically inputs the required logistics lists.
Yes i'm aware but to me that is still somewhat "manually" , i can see how there's some part of automation, depending on your goal the distinction may or not be insignificant.
spesest wrote: Mon Dec 22, 2025 10:56 pm I'm contemplating this specific circuit network or method. While it feels feasible, building the concrete system doesn't seem easy, so I'm requesting assistance.
It does feels feasible, but it's unclear for which part you need assistance, and you are expecting very precise result and way of achieving it.

I can share blueprints from the builder train i'm using in my current game :



It's not a fully fledge system that remove excess material nor "deliver" precise amounts, because im ok with little excess unload , and it's using "disable station" instead of setting the limit to 0, which should be changed if the plan is to ever use more than 1 train but it's a functionning proof of concept with one load station and one unload station, and it can be used with that thing you described where you put a blueprint in the constant combinator to setup the list of material instead of the list used in the example. I thought of it as a mini version of the video you linked where nothing is too complex or too fancy if there is anything you wanna ask on it. But if you need more precise assistance it should probably be one step at a time and with some of the part you're trying to make as input.

Re: how to make builder train

Posted: Tue Dec 23, 2025 12:00 pm
by Nosferatu
Here is a count perfect loading station that I used for my build train pre v2
viewtopic.php?p=514368#p514368

But that breaks if you try to use it for ALL building materials.

I think you need a setup where it overloads the train and has an inserter on the other side to pull out excess materials. (Override stack count =1)

Ltn used to have a "locked slot" option. Use this so that the last slot in your build train stays empty.
Otherwise inserters will get stuck with items in their hands.

Edit: in case you want an easy way out of your challenge:
This mod: https://mods.factorio.com/mod/Constructron-Continued

Re: how to make builder train

Posted: Tue Dec 23, 2025 1:01 pm
by Tertius
You just need to carry a little bit of everything, not vast amounts. At least not for rarely used items like reactors. Just one or two.

This is an example of the supply train I use. It's able to handle multiple wagons with multiple items and will load and unload exact amounts of items, and it includes garbage collection. Make sure the logistics network of the unloading station isn't connected to any other logistics network providing their own items - it will pull everything not in the station stock definition as garbage into the train. If this is not desired, remove the appropriate circuits and buffer chest from the station.

loading:
12-23-2025, 14-06-52.png
12-23-2025, 14-06-52.png (1.7 MiB) Viewed 175 times
unloading:
12-23-2025, 13-41-18.png
12-23-2025, 13-41-18.png (1.04 MiB) Viewed 179 times
loading:
Unloading:

The schedule, interrupt driven plain vanilla. It's able to chain deliveries to multiple stations as long as any stock in the train isn't exhausted. This chaining is not what you need with your current task, however it's there and the reason why the "Supply delivery" interrupt condition has some more entries and the unloading station does more with the unlock signal than immediately visible.
12-23-2025, 13-59-12.png
12-23-2025, 13-59-12.png (151.47 KiB) Viewed 179 times
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