This is actually a prototype a did months ago, when first thinking about the project. Back then I had started with the idea of only using two lugs per side on the hinge, where the screws were set in permanently, and the modules slid together sideways. A cylinder held in place by the jumper (here shown as a piece of black cardboard) would then hold the two inner lugs apart. It worked reasonably well, but essentially relied on the jumper staying on place (being a piece of cardboard, it did not).From there, I've moved on to the idea of using 3 lugs on each side, holding themselves in place when attached. I was initially skeptical that these would be strong enough, as when using a screw with 4mm of thread, each lug is only just wider than 1.5 mm. I'm still getting used to SCAD, so these were drawn up in SolidWorks. Printing at 0.15mm seemed to work okay, they are suprisingly solid around the hinge points.

Something that probably needs pointing out here is that these basic module shapes are flat ( as opposed to a concave base). This is going to be more important with longer modules, but I'm yet to figure out a good way of printing them with such a shallow overhang. Of course, the whole thing could be tipped on its side, but then the lugs become small features overhanging horizontally, which in my experience never work out well.