Lets talk about how to make or find realistic eyeballs (with or without cameras in them) and how to mechanicaly hook them up so that they will move side to side, up and down and have eyelids and moving eyebrows.
We could study anatomy text books and look at models to see how big the eye is and how many parts and colors it has such as the iris which dilates, the lens, the red veins that surround the eye etc.
There are crafts people and doll makers who are incredibly good at making ultra realistic glass eyes and eye parts for use in robot applications.
Now once you figure out what you want the eye to look like and do, you must figure out a way to design or find a design that moves your eyes and has the brackets for the motors.
Old simple toys like the Furby had a series of linkages and gears that would move the eyelid and the mouth together and although the eyeball didn’t move, it looked and still looked incredible and to many people it looked and sounded creepy.
Then you have the Gemmy animatronic dancing santa clauses and the Gemmy Edwardian butler which had eyeballs that moved side to side in a very creepy fashion and as a sidenote it also had a chest that heaved in and out as if the doll was breathing along with its breath sounds that it made.
So you can pick and choose from how other toys and robots make their eyes move or find a 3d printed eyeball mechanism site on sites like thingiverse and go from there.
Some robot eye mechanisms may use one servo per eye and one per eyelid so you need to try to reduce the number of motors needed.
Here are some great Youtube videos that show how to put together eye mechanisms:
- John Strope https://www.youtube.com/watch?v=xf6xtEhTiz0
- Will Cogley https://www.youtube.com/watch?v=Ftt9e8xnKE4&t=5s
- James Bruton https://www.youtube.com/watch?v=jsXolwJskKM&t=558s
- Toy Machines https://www.youtube.com/watch?v=XW5VFjakc68
- Kevin Felstead https://www.youtube.com/watch?v=-XpzTU8Hep0
- RimstarOrg https://www.youtube.com/watch?v=DY4as7Lc9KY
- MisteRoboto https://www.youtube.com/watch?v=2zQ48pSsCb8
- Neelco 2018 puppetry https://www.youtube.com/watch?v=JBwxq0ZbPio
If you look at the inside of the Mesmer robots from Engineered Arts you will see chain drives operating some part of the face perhaps the mouth or the eye or the cheek area.
You want to avoid to many noisy motors and the accompanying weight and heat generated and the strain on your batteries.
There is a vast amount of great information on making moving skulls and more on the Instructables sites like this part here :https://www.instructables.com/Automated-Talking-Skull/