This is an older project, but the electromechanical solution used to create this giant, staring eyeball is worth a peek. [Richard] and [Anton] needed a big, unblinking eyeball that could look in any direction and their solution even provides an adjustable pupil and iris size. Making the pupil dilate or contract on demand is a really nice feature, as well.
The huge fabric sphere is lit from the inside with a light bulb at the center, and the iris and pupil mechanism orbit the bulb like parts of an orrery. By keeping the bulb in the center and orbiting the blue gel (for the iris) and the opaque disk (for the pupil) around the bulb, the eye can appear to gaze in different directions. By adjusting the distance of the disks from the bulb, the size of the iris and pupil can be changed.
A camera system picks out objects (like people) and directs the eye to gaze at them. The system is clever, but the implementation is not perfect. As you can see in the short video embedded below, detection of a person walking by lags badly. Also, there are oscillations present in the motion of the iris and pupil. Still, as a mechanism it’s a beauty.
In the video you can see the eye lag behind detecting the person, but you can also see the iris and pupil appear to bounce as they move. This can happen if the motors are too weak or the load is awkward; the motors end up constantly overshooting then overcorrecting as they struggle to move a load that is too heavy or poorly balanced for them. Slow and steady movement is probably fine, but faster and bigger movements will oscillate more.
We recently saw another eyeball project from [Richard] with his flipping eyeball broach, which is like a really stylish 1×1 flip-dot display. And if you happen to detest eyes for some reason, you’re probably interested in this robot whose entire purpose is to find eyeballs, then shine a laser into them.