I've created the 3D design of these hinges, for my Rocket Drone (which has a hybrid motor). Basically, it can be launched using a rocket model motor (common Estes Rockets stuff), and it can be retrieved using the electric motors of the quadcopter, landing the rocket vertically (SpaceX style).
Anyway, even though I've designed these hinges with the Rocket Drone in mind, they can be used to improve the portability of the common and very popular WLtoys quadcopter, (provided with 5mm square carbon shafts).
You need also 8 x Extension Springs: Diameter0.5cm Length 0.8cm 14+2 Windings for the hooks (Hinges)
and 2 small paper clips to create 8 metal axis for the hinges.
By the way, all these mods nearly affect the AUW of the quadcopter, that it still below 250 grams (hence it doesn't it to be registered, because it complies U.K. Laws).