I’m currently making a sphere robot that is basically a BB8 droid and have just finished the prototype. I got the parts for the inner motors from a robot making kit I got a while back. For the head, I made my own ball bearings so that it rolls smoothly over the outer shell of the ball. It is attached by magnets to the inner workings that stay up right the entire time. My next step is learning how to use a 3d printing software and making everything run more smoothly.