Impossible to build or bug?

[Agricola]

I have been trying to build a couple of features which require a template part to place two docking rings on main section, however when I select this template I only get one green construction ball, is this a bug or just a stupid bad bit of coding which only allows one join to be active. See screen shot below, notice the selected parts with just a single green ball, can not even stick docking ports to side of tank.

Edited August 20, 2014 by Agricola

[Mesons]

More information would be helpful, like the steps you used to build the sub-assembly, but I suspect you are suffering from the part hierarchy coding. Every time you add a new part, it becomes a "child" of the part you stuck it onto, which is the "parent" part of that child. In this way, every part has a parent except the root part, which is always the first part you place. When you drop a collection of parts into a sub-assembly, the part you grabbed (with all its children attached) is made the root part of the assembly. Where that part was attached to its parent will be the only place you can attach the assembly.

You'll need to build your sub-assembly in such a way that you pluck it off the craft to save it from the same point at which it will be attaching. If this isn't the problem you're experiencing, post more details and perhaps file a bug report.

[juanml82]

A subassembly can only have one green ball, so I guess you'll need to duplicate one of the parts

[MockKnizzle]

The building system in KSP works like a tree: there is one "root" part that all other parts are sequentially attached to. When building normally, this is usually the command pod (you can check which part is the root part by grabbing it, the whole craft will move intact if you grab the root). A limitation of KSP's part-tree system is that you can't have branches re-connecting back to the tree to form connected loops.

Subassemblies work in the same way, when you grab an assembly and save it, the part you grab becomes the root part of that assembly. You will only have an active attachment point on the root part of a subassembly. This means that it is impossible to connect branch-to-branch, which seems to be what you are trying to do.

[Agricola]

OK thanks hierarchy makes sense then, so I was wasting my time then, back to the drawing board and try to work out how to do this. It would be a nice future request to have all points available in a sub assembly active.

[Sirrobert]

OK thanks hierarchy makes sense then, so I was wasting my time then, back to the drawing board and try to work out how to do this. It would be a nice future request to have all points available in a sub assembly active.

I suggest you get the mod Select Root. This will allow you to change the root of a craft after you already built it.

With this function added, you can build your subassambly like normal, and when it's time to save, you switch the root (the new root being the part you attatch to the rocket. In this case, the docking port), and save.

If you don't want to use the mod, just rebuild this subassambly, it's not to complex. In this case, the first part you place would be the docking port