Via Yahoo.com:

From the moment BB-8 made its debut in the teaser trailer for Star Wars: The Force Awakens, fans have been trying to figure out how the rolling robot works. Once the world learned that the droid was a real prop, not a CGI effect, speculation went into overdrive. Lucasfilm has yet to reveal how BB-8 operates — how does it stay upright while rolling? Is the head attached to the body? But two Star Wars fans in Spain, Carlos Sánchez and Emilio Gelardo, believe they have cracked the code.

“Truth is, 80 percent of the information was already out there. So our job was putting all those pieces together and filling in the gaps,” Sánchez, a web developer with a background in engineering, tells Yahoo Movies.

On their website HowBB8works.com, Sánchez and CG artist Gelardo have created a 3D model of the rolling droid, with a toggle that allows visitors to see inside the ball. The model illustrates two possible interior mechanisms for the robot: One that has the head attached to a vertical mast, and another that positions the head on a rotating, arc-shaped axis. (In both designs, the head is magnetic, and the sphere moves with four internal wheels and orients itself with a gyroscope.)

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