For people coming to Foundry as their first factory game the term "Main Bus" might not make too much sense initially but hopefully by the end of this guide you'll have a decent grasp on not only what they are but some basic understand of how to effectively use them to keep your factories from turning into a mess of conveyor spaghetti.

The term main bus comes from computing where it refers to a single line transferring data between two points which is exactly what we're doing here but in our case it's items that are being sent! For those who are curious[en.wikipedia.org]

Our buses will consistent of long lines of belts in parallel, items are taken off the main bus and turned into other items where they are placed back onto the bus or placed into storage for use later by the player. The strength of this approach is that no matter where you are on the main bus you will always have access to the resources that you produced further up the line which means this layout is extremely easy to adapt when encountering new items that you need to produce in order to progress.

It's because of the reasons above that a main bus is generally what I would consider to be the best way to learn a factory game due to that flexibility as you don't exactly know what resources you will need later and in what quantities therefor having access to everything at once makes things a heck of a lot easier.

The aim of this guide is primarily to show some good habits to have while constructing your main bus rather than to give you a carbon copy layout to follow each time you start a new save.

The first thing we need to do is look at our map and plan which direction our bus will go. At first our base will be small but as we expand our factory our main bus will get quite long so it's important to check that you have enough space to expand your belts without bumping into a mountain that you didn't expect to be hitting quite so soon.

For this example we will just be making a North to South bus; this is just the direction our belts are going to be going as shown in the graphic (arrows annotate belt direction)

While you can turn a main bus later on if you find that you have run out of room and have no other option it's generally just something you try to avoid.

Another important part about planning is the how many belts do we want to group up? how much of a gap do we want to leave between belt sections? in other games like Factorio as an example this matters more as the early game underground belts have a 4 tile limit so most main buses would look like this; 4 belts - 2 wide gap - 4 belts - 2 wide gap ect but in Foundry we have no such limitation so you are free to make your belt sections as wide as you like however that being said you should try to keep them multiples of 2 to allow you to more easily balance belts later on.

As a general example though lets just assume we're going to be using the 4 belt - 2 wide gap - 4 belt layout mentioned above and move onto the next step.

Now we have to think about how will we get our items off the main bus or back on when we need to use them and it's actually fairly simple. I mentioned earlier how we should try to keep our belt width multiples of 2 well now you will see why we did that! on the right is our belt splitter, the purpose of this arrangement is to try to preserve the throughput of our belts in the case of an overflow.

If we were to use something else like this other belt splitter (Bottom image) while we would get the same result of a single belt coming off the main bus line but notice that you would be completely stopping the flow of the closest belt so the total throughput of the belt is cut in half as a result. For the rest of that belt line you would only be able to provide a maximum of 160 items/min since you have a single MK2 belt (320 items/min) splitting into 2 Lines of 160 items/min.

You don't need to know the technical side of this exactly to be able to make an efficient main bus but it helps to know what you're doing and why you're doing it. Simply put though you should use the top example of a belt splitter to preserve throughput down the entire main bus.

It's also worth mentioning that in Foundry you can set priority outputs on balancers (this is done by clicking the small switch on the output side of the balancer) the side that the switch is set to will get first dibs on any items that enter the balancer so this can be very useful if you want to make sure that one of your production lines gets priority on any incoming resources.

Putting items onto the bus is done in much the same way, you can even use the same design as your output splitter but instead of taking a belt from the front you just put a belt into the back as shown below.

This section will be brief but it's extremely important that you balance your belts periodically throughout your main bus a 4 lane balancers like the one shown here are extremely easy to make and doesn't take a lot of space to make which is why I generally favour 4 belt wide main buses. The reason we have to balance our belts occasionally is that at each of our belt splitters we're taking items from a single line and sending it elsewhere but you have 3 other belts that may not be fully used so you want to be able to fully utilise all of your resources and that's the value in balancing; you can spread the load across all of your belts at once. While balancing is helpful you should also make an effort to try to alternate which set of belts you're taking items from so you don't have to balance your belts as often but generally if you're seeing one belt is almost completely empty in your main bus but the other belts are almost completely full then it's time for a balancer.

We need to think about how we lay out our production lines now that you have the basics of managing your main bus down.

Initially you need to get the most basic resources onto your main bus, in this example that's going to be Xenoferrite Plates. You should be thinking about how much of this item you think you might need but I'll help you out here and give you some ideas at the end of this guide for what kind of ratios of each item you want on your main bus.

Xenoferrite plates while not used directly for too many things are used to make machinery parts which will be needed a lot later on so we're going to dedicate 4 whole belts to just Xenoferrite Plates for now and we're going to try to make our furnace array tillable as shown below.

(For reference C1 Refers to MK1 Crushers while S refers to Smelters, arrows are belts + their direction, blue rectangles are input loaders and orange rectangles are output loaders)


Notice there is a gap between the closest belts above the final crusher of each line - this prevents ore rubble from entering the output line of the smelters

This design relies on the T2 Smelting recipe to function so if you plan to copy this just make sure you have the "Ore Refinement" technology unlocked

The output of each line feeds into the start of our main bus and will continue to travel straight down until it's needed again. The same setup is used for Technum rods as shown below



The reason we have 5 of these but only 4 Xenoferrite plate furnace stacks will become more clear shortly but the general idea here is that we're using the same layout for each process when possible, all we're doing is changing the recipe. Spending a good amount of time designing something that will be used multiple times with only minor changes speeds up progression a lot when you know exactly how you're going to design the next production line without having to go back to the drawing board each time.

Now you will find out why we went with 5 Technum rod smelters instead of 4 like we did for Xenoferrite plates. The simple answer is electronics. Technum rods themselves are not used very often but they are the only ingredient needed for electronics which are used in almost everything so we're going to turn 4 whole belts of technum rods into 2 belts of electronics and keep only a single belt of technum rods for later user in our main bus, this will be more than enough for a long time.



We're going to do the same for machinery parts now but we're only going to turn 2 belts of xenoferrite plates into machinery parts as the ratio is 1:1 and plates have more use in later recipes than the technum rods do.



Even though I've shown MK2 Assembly machines here you are not required to use them, I've simply used MK2 machines here to show the correct ratio of input to output and I encourage you to spend time coming up with your own designs and find ratios that work for the tier of machines you have access to - it should also be said that you don't need to fully build these layouts exactly as they are immediately, you can partially build each of them to temporarily supply your base with materials and expand them later when more items are needed

Something more unique about Foundry is that while the idea of a main bus may have originated from Factorio we're not restricted to a single dimension, we can stack belts on top of each other if we later find out that we actually didn't leave enough space on the bus but if you do end up doing this just make sure you're leaving enough space between each layer of your bus so you don't restrict yourself from accessing belts further into the middle of your bus, leaving at least a 3 height gap between layers is probably the minimum I would say but more is always better here. The nice thing about a main bus is that you're not building spaghetti belts to gain access to your resources so try not to fall into that trap and make sure you always give yourself more space than you think you need in order to expand later on.

If you go down the route of stacking your main bus into layers you can use freight elevators to access the items at those higher layers. Just make sure you're leaving 4-5 tiles of space between your main bus and any machine rows you build so you have space for them later on.

The simple answer is; everything.

But there's more to it than that really. You should put as many different types of ingredients on your main bus as you think you might need, anything that was missed or overlooked you can always add it in later. That's the fun thing about building a factory like this. The important thing is how much of each item do you put on the belt?

You would likely need to play through the game and learn from experience to be able to figure this out on your own and get an idea of how many belts of each item you would need but I'll help you out here. (These are going to be ratios so you should adjust them according to how big you want to build your factory and keep in mind that a main bus factory best suits a starter base so later on you may actually be moving away from this style of design in favour of much more focused production lines but that's something you can decide later)

• 2 Belts of Xenoferrite Plate
  
• 1 Belt of Technum Rods
  
• 4 Belts of Electronics
  
• 4 Belts of Advanced Machinery Parts
  
• 2 Belts of Machinery Parts
  
• 2 Belts of Advanced Circuits
  
• 1 Belt of Energy Cells
  
• 1 Belt of Concrete
  
• 1 Belt of Polymer Boards
  
• 1 Belt of Glass
  
• 2 Belts of Steel

Throughout this guide I've cited a bunch of layouts from a sheet, if you want to view the full sheet I'll leave a link here[docs.google.com] for you to take a look at in greater detail.

I took a lot of inspiration from Falk's guide in how he showcased some layouts when writing this guide so wanted to make a mention of this here and recommend everybody to check it out here