Developable mechanisms can reside inside the surface of a structure

Engineers detail new technology that allows them to build complex mechanisms into the exterior of a structure without taking up any actual space below the surface. This new class of mechanisms, called 'developable mechanisms,' get their name from developable surfaces, or materials that can take on 3-D shapes from flat conformations without tearing or stretching, like a sheet of paper or metal.

from Engineering News -- ScienceDaily http://bit.ly/2BD0R3f