I'm currently in the process of making a Halloween contraption that has a few components that are worth documenting. The Huge Arduino Animatronic LED Eyeball is one of them.
Most animatronic eyeball projects that I found were more or less life-size. They were usually ping pong balls or dolls eyes or 3-D printed. I needed something bigger. I needed it to proportionally fit into a 2-ft diameter sphere. It didn't need it to be high fidelity, though it did need to look kind of cool (otherwise the kids would think it was lame). I wanted to keep open the ideas of a cyclops or a 2-eyed monster. It needed to be animated to appeal to kids. Illumination was optional. The project itself couldn't be expensive nor overly complicated. Finally, after Halloween was over, I wanted to be able to dismantle everything and reuse the parts for future projects.
There are only a few key items which make this project successful, IMHO. The first is the Westinghouse clip-on shade. It's the perfect size and shape, lightweight, translucent, hollow, and cheap. The second is the 1/4" socket wrench universal joint in conjunction with the 11/32" brass tube. I tried a RC universal joint but it way too floppy. The socket wrench universal joint has enough friction to create a tighter movement. It also has enough degrees of freedom for this project. The brass tube provides a very snug fit over the joint's male connector. Together they make a very nice rod and joint (more like tube and joint) system. The last item is the Coroplast. It is lightweight, rigid, and easy to cut. When cut perfectly to the inner dimension of the clip-on shade, it provides a very snug fit especially when pushed into the shade a bit. It won't rotate or accidentally fall out (at least it hasn't done so yet). And it can be popped in and out of the shade without it starting to fail. I originally had tried foam board but it started to bend and loose its rigidity. Thin plywood was my other choice, but it seemed to heavy.
As for the rest of the parts, use whatever works for you.