It might be a little difficult to see but, trust me, it's there... Unfortunately, the actual rod and rod end is not there because I don't have any dimensions for one so I eyeballed it and gave me enough room to modify the parts a little bit in case they don't fit perfectly at first.
EDIT: Here's an image of the head tilt with *temporary* linkages connecting the servo and the ball and socket joints for your viewing pleasure.
This image shows the part moving in 3 dimensions. For example, if both servos rotated in sync and mirrored, it would tilt the head up or down. If one moved instead of the other or different amounts, it would start rotating and tilting at the same time. Of course in the final design, instead of the linkages, there will be a rod end and a threaded rod connecting the servo arm and the ball and socket joint on the bottom.
Next up is going to be the eye tilt. I still have a few more hours tonight to work on it so maybe I can get an proof of concept design in there somewhere. Once that's done, I'm thinking about putting a 3 axis accelerometer in both of his eyes so I can use a closed loop feedback for the head tilt as well as for his eye tilts. Three axis accelerometers (with breakout boards in place) are about $12 each but if I make them myself, I can get the IC for about $5-6. We'll see...
The one thing I'm having trouble with is finding the right size servos for his movements. I'm trying to find the most economical yet powerful servos, steppers, and motors but who knows what'll happen when it's time for the real thing!
Alright, like I said, it's time for the eye tilt tonight and then I'll get started with the neck tomorrow. It's going to be very interesting to see if I have enough room for what I want to do in there. Essentially, it's going to be like a robotic arm driven by several timing belts and pulleys. The thing I'm most worried is about vibrations and shaking of the head when WALL-E is moving and stopping. Rigidity is the key!