by Vagabond Carter

So by now we’ve all seen BB-8, R2-D2’s football (European style) cousin of a droid do the seemingly impossible by rolling out on stage live at Star Wars Celebration.

If you haven’t: What rock were you under today?!

This reveal put the absolute last nail in the theory that the little rolling droid was some form of CGI effect, in direct contradiction to Director J.J. Abrams statement that he would be relying on practical effects where possible.

So the question is: HOW?

Conventional wisdom tells us windmills and beach balls do not work that way, that it has to be some trickery… and it is… but I’ll get to that in a moment. Let’s look first at BB-8 itself:

BB-8 from 'Star Wars: The Force Awakens' rollin' along

BB-8 from ‘Star Wars: The Force Awakens’ rollin’ along

Before today’s reveal I was willing to believe that the lower ball was in truth only half a ball, namely the side facing us, with the head on a stick running along a track rotating the lower ball underneath it. And that may in truth be one of many ways this little droid gets it’s screen-time. But what about the onstage appearance? This is a pretty impressive magic trick. Let’s note a few things:

  1. There is no gap in the ball.
  2. There is no single preferred direction of rolling for the ball either.
  3. The ‘head’ appears to lead the motion slightly.

That last one may be most telling of all, as we’ve seen that before in a much more mundane device: the Segway.

Vader in a Segway, no really.

Darth Vader on a Segway, no really.

The CMU Ballbot, the first successful ballbot, built by Prof. Ralph Hollis (not in picture) at Carnegie Mellon University, USA in 2005.

The CMU Ballbot, the first successful ballbot, built by Prof. Ralph Hollis (not in picture) at Carnegie Mellon University, USA in 2005.

These somewhat silly scooters came out in 2001 and operate on a then new and now fairly well known system of sensors and servos to balance the device, moving it forward as you tip it forward in the process. This is exactly the behavior we see in the on stage BB-8 hero prop. If we miniaturized two Segways setting them at 90 degrees to each-other and placed them in the ‘head’ A single magnetically attracted ball could act as a universal wheel system. This might give us exactly the behavior we saw on stage!  BB-8 therefore is just the “head”, and the ball is little more than the droid’s shoes!

BB-8 is what’s called a “ballbot” – a dynamically-stable mobile robot designed to balance on a single spherical wheel (i.e., a ball). Through its single contact point with the ground, a ballbot is omnidirectional and thus exceptionally agile, maneuverable and organic in motion compared to other ground vehicles. Its dynamic stability enables improved navigability in narrow, crowded and dynamic environments. The ballbot works on the same principle as that of an inverted pendulum.  The first ballbots were pretty large and ungainly, but BB-8 takes the ballbot idea to the logical extreme.

Tying it together are some pretty sophisticated radio controls and electronics for balancing that head on the ball so that it never actually falls off. Sooner or later somebody outside of Lucasfilm is going to figure this out.

What’s this mean for conventioneers? Watch your step folks – the BB’s are rollin’ in!

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