I am currently attempting to build a basic orbital refueling station. I've been watching a few tutorials, mostly those of Matt Lowne and Scott Manley, and they have been very helpful. In my current attempt, I am trying to more or less copy part of a station that Matt Lowne demonstrated in this video. The part that I'm copying starts at about the 2:10 mark. I don't know if it makes a difference, but I'm using fuel tanks instead of crew quarters. The shape of the parts is the same. Also, I'm just doing the octagon, not trying to make it rotate. It looks fine in the VAB, but once I move to the launch pad and the physics kick in, it's obvious that I'm missing some aspect of the construction.
I made a short video if it helps. It all just starts flopping around.
As long as this game has been out, I'm guessing that this has been addressed somewhere. I did look around a bit for a solution but couldn't find one. It won't look as cool, but if all else fails I'll just go rectangular.