My DIY BB-8: Problems, Solutions, Lessons Learned

Imagine trying to make a ball-shaped robot that rolls in any direction but with a head that stays on. When I saw the BB-8 droid doing just that in the first Star Wars: The Force Awakens trailer, it was an interesting engineering challenge that I couldn’t resist. All the details for how I made it would fill a book, so here are the highlights: the problems I ran into, how I solved them and what I learned.

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How BB-8 Works Revealed At Star Wars Celebration Europe

Finally the workings of the official BB-8 that you’ve seen rolling around at various events have been revealed. Its makers [Matt Denton] and [Josh Lee] participated in an hour-long presentation at Star Wars Celebration Europe 2016 just this past week where the various views of its internals were shown in action. It’s since had BB-8 builders (yours truly included) analyzing the workings for new ideas. We also now have the official name for it, red carpet BB-8.

For the first half of their talk they went over how BB-8 was implemented for Star Wars: The Force Awakens. As we’ve long known this was done using 7 puppeted BB-8’s, though it was revealed that only 4 were actually used, including a stationary one called the wiggler whose purpose you can guess. Another thing we didn’t know is that they did consider building a working BB-8 for filming but decided they needed something bullet proof, that would work right every time without making a film crew wait for repairs, and so went with the puppets instead.

The second half of their talk contained the big reveal, the mechanism inside red carpet BB-8’s ball. It turns out to be pretty close to what many builders have been doing. If you’ve seen the DIYer’s guide to the different BB-8 drive systems then you’ll understand when we say it’s a pendulum drive (aka axle drive). That is, there’s a motorized axle that crosses the middle of the ball and the ball rotates on that axle. Meanwhile a large mass suspended below the axle acts as the pendulum mass.

BB-8 builders have known the importance of keeping as much mass as possible as low down as possible for stability, but it was revealed the great extent to which that has been done in the red carpet version. Motors for the head’s pitch and yaw are located at the bottom and their motion is transferred up to the center using what are maybe best known as bicycle brake cables. Another big reveal was a linear actuator for the body roll, tilting the center stuff with respect to the mass lower down. The actuator itself is located in the lower section. Also, BB-8 builders have been mounting the drive motors for rotating the ball with respect to the axle, in line with the axle. However, in red carpet BB-8 the motor is also at the bottom and its motion appears to be transferred up to the axle via belt and worm gears. You may mistake the gold cylinders on either side of the central gimbal system to be motors but they’re actually Moflon slip rings.

Those are just a few of the insights gained so far from analyzing the video below. Doubtless people will be noticing a lot more in the weeks to come.

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Driving BB-8: More Than One Way To Move This Bot

BB-8 is the much loved new droid introduced in the 2016 movie Star Wars: The Force Awakens, though in my case from the very first trailer released in 2014 I liked it for the interesting engineering problems it posed. How would you make a robot that’s a ball that rolls along, but with a head that stays on top while the ball rolls under it?

To make the ball roll, the answer most people found obvious at first was to use the analogy of a hamster wheel. The hamster running inside makes the wheel turn. In the BB-8 building world, which is quite large, the drive mechanism has come to be called a hamster drive, or just a hamster.

Magnets holding the head on
Magnets holding the head on

For the head, it seemed obvious that there would be magnets inside the ball, perhaps held in place near the top of the ball by a post extending up from the hamster. Corresponding magnets in attraction would then be attached to the underside of the head, and balls (also mounted under the head) would keep the head moving smoothly over the ball.

The magnet approach for the head has turned out to be the method used by all BB-8 builders that I’ve seen. However, the hamster has turned out to be only one of multiple solutions. Since the original debut many different methods have been used in builds and we’re going to have a lot of fun looking at each separate approach. It’s almost like revealing a magic trick; but really it’s all just clever engineering.

Note that for the actual movie, a combination of 7 or 8 props and CGI were used. The official working BB-8s that are shown at various promotional events were built after the movie was made and as of this writing, few details of their construction have been released. One notable detail, however, is that they aren’t using hamster drives.

Below are details of all the different BB-8 drive systems I’ve seen so far that have been built along with how they work.

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The Scientific Implausibility Of Starkiller Base

This post contains spoilers for Star Wars: The Force Awakens. These spoilers won’t affect you if you haven’t seen the movie; they’re equivalent to saying, “in A New Hope there’s a moon sized battle station with a superlaser” and “someone gets a hand amputated with a lightsaber in a Star Wars movie”


A lot has happened in the Star Wars universe since the battle of Endor. The Empire is in ruins, and Yavin 5 and the forest moon of Endor both have new planetary ring systems. The Rebellion has given way to a new Galactic Republic, but there is a spectre of evil looming in the unknown areas of the galaxy: the First Order, a malevolent force that has built a planet-sized superweapon capable of destroying entire planetary systems from across the galaxy. The Starkiller gets its energy from harvesting entire suns, moving from one solar system to another to feed this massive weapon of terror.

We’ve had nearly forty years to argue the plausibility of the Death Star, lightsabers, parsecs as a unit of time, and hyperdrives. It’s time to pass the hallowed tradition of arguing over fictional spacecraft to a new generation. Starkiller Base is a cool idea, but does the science behind it hold up? No. It’s completely implausible. It makes for a great story, but it’s completely implausible.

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