This blog will be an ongoing mind dump as I plan out my build of a roughly half scale “working” version of an Aperture Science Personality Core, specifically: Wheatley. Here's the first video intro of my series.
For the uninitiated, Aperture Science Personality Cores are spherical robots from the Portal game franchise. They are highly articulate eyeball robots with arguably sophisticated AI that allows them to run various aspects of Aperture Labs and most importantly, moderate the behavior of one particularly naughty AI who is the central core of the facility.
(Photo credit: https://animatronicwheatley.com/getting-started-guide/ )
As you can see, I've got my work cut out for me! Like most video game characters, he might seem plausible at a quick glance, but looking in detail reveals he bends if not outright breaks many laws of physics 
While there might arguably be more, I've settled on creating him as an animatronic with 14 degrees of freedom:
(His iris mechanism will be digital, so I'm not counting it as a real mechanism, but will be included)
- (2x) independent handles
- (2x) independent eyelids
- (2x) inner eye (pan and tilt)
- (6x) eye ring Stewart platform
- eye ring axial twist
- inner sphere rotation
Mechanisms that cheat:
- eyelids - In the game they disappear into the space of the outer ring. This can just be ignored so that they just peek out the edges.
- spring-loaded arcs - The orthogonal arcs that run along the core of his body make no sense. While it seems like they just rotate about his main axis, they completely intersect with each other at the rear, are not visibly supported by any component, and the horizontal arcs pass through the side axis shafts, yet have no slot for the shaft to pass through. I've opted just to include short, fixed portions of these arcs towards the front.
- inner sphere rotation - While it's almost possible for the inner sphere assembly to fully rotate in real life, the edges of his outer eye ring clip through the mechanisms that support and drive the handles. If the handles were static, this could be achieved, but, then we get to the issue of there being no visible axle about which this rotates. In theory, there could be a large shaft supporting the two outer, side shells to allow this, but the Stewart platform would intersect this if the inner eye twists... so I've just settled for allowing a 30 degree sweep, which will be enough for expression.
Core Element One: The Inner Eye.
Even describing Wheatley's mechanisms is a challenge as he is essentially entirely an eyeball, but the medical terminology quickly falls apart. Aside from the fact that he's a fantastically charming character, he's highly articulated too, which I like as a mechanical engineering challenge, but honestly, the real reason I started this build was because I found this beauty on Alibaba: 
A fully circular, 5 inch diameter LCD with an HDMI driver board! It's pricey at $200, but just sooo cool. For all intents and purposes, it's a 1080x1080 LCD where the pixel outside of the circumference just aren't displayed, so using it is just the same as any other monitor. In the game the colored element only modulates in brightness slightly as a VU meter when he speaks, so this part could have been a printed, backlit image, but using a display will allow me to display the eye patterns of all of the other cores from the game and, well, use as a main monitor for the Raspberry Pi...
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