I really love the design of the communicator prop from Star Trek: Discovery. It's a sleek, cool original design that incorporates cues from the TOS and TWOK communicators to ground it in the lore of the show. It just screams Trek as soon as you see it.

A behind-the-scenes props video from September 2017 gave us a fantastic look at the innards of a hero communicator. It’s really very elegant in its simplicity -- the communicator is essentially an elaborate CNC machined aluminum housing for a 7th generation iPod Nano. The only working feature in the metal itself is the lid spring mechanism.

This printable communicator is designed to be assembled in a way (and with a lid mechanism) that mimics the original as closely as possible given the current available reference. Not pictured in the renders are the eight socket head screws that hold the parts together as on the original. I omitted the threaded inserts that are visible on the original.

The BTS video is not clear enough to see what the actual attachment of the spring to the hinge pins is, but this is what I came up with. An extra stainless socket head cap screw acts as a pin for the spring to hook onto and rotate about. This acts to pull and hold the lid shut when rotated past a certain point, and to pull and hold the lid fully open going past that point in the other direction. Two springs loop over a fixed brass (steel?) bar that spans the comm body cavity; the other ends of the springs appear to be attached (off-axis) to the lid hinge pins. The springs are constantly under tension, with the points of least strain being the lid fully open and fully closed.

The image with the test print demonstrates the hinge function. From left to right: Fully closed lid, lid open to neutral point with maximum spring extension (where the lid is rotated such that the spring falls exactly across the axis of the hinge pins), and on the right, fully open lid. The hinge pin pieces also incorporate physical stops that prevent the lid from rotating past 130 degrees.