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.

The following video plays where they start talking about the puppeted BB-8s for the movie. For the talk about the red carpet BB-8 and its internals skip to around 35:44.

[via BB-8 Builders Club]

17 thoughts on “How BB-8 Works Revealed At Star Wars Celebration Europe

    1. “Lots of lost energy there.”

      for my own edification here, what would be a smarter, less energy losing way of accomplishing that?

      I need some help here. Rigid linkages? there appears to be a trade off they must have felt worthwhile.

      1. I can’t think of any alternative method, short of moving the motors up higher. That’s clearly what they didn’t want to do. However, many builders do have their motors higher up and have had very good results, though none seems quite as stable as the red carpet BB-8. They are fairly stable though, and make up for it with more mass lower down.
        It seems to work just fine, so lost energy or not, I’d go with it if I were making a full sized one (mine’s 3/5 scale.)

      2. For the short operational times required, the efficiency hit from Bowden linkages is more than made up for by the flexibility granted by them. You get decoupling of hard impacts from the drive train, freedom of placement of driving motors, angular alignment freedom, neato factor… probably male enhancement?

        Who knows.

        Rigid linkages would be much more energy efficient. Hub motors would be efficient, but would put a ton of mass above where you want it in a pendulum drive system.

        1. Not to mention their “springiness” in twisting motion and lag time in both tension and twist likely adds a LOT to the “natural” motion of the character that a hard linkk might not have. You can add it through programming or puppeteering, but the Bowden cable is a natural mechanical “character effect”.

      1. How about the possibility that he is correct? Even “the absolute top people” make mistakes sometimes, but more likely they _know_ that there are more efficient ways to do it but for _reasons_ they choose to go with those cables…

  1. Crawled the web for some definitions on “Moflon slip-ring” but only found the manufacturer , some FAQs and product specifications, but no word on what these things actually do… Could someone care to explain please?

    1. Slip rings are generally used to transmit electrical signals across a continuously rotating boundary — effectively using small brushes / springs on one side to press against a conductive ring on the other side (thus slip ring). There are a couple illustrations here: https://en.wikipedia.org/wiki/Slip_ring

      It looks like Moflon is a manufacturer of slip ring systems, many of which support multiple / high speed connections.

      1. Jonny nailed it! As for other diagrams, Google led me to this page which has a pretty extensive breakdown of the Who, What, and Where of slip rings – http://powerbyproxi.com/slip-ring/ – if anyone’s interested in diving deeper (it’s kinda nerdy, I’ll admit, but I love stuff like this so…). That said, this BB8 is a great example of some of the less common uses for these things. Usually you’d find them in industrial equipment, but BB8? Always knew that thing was a trooper. (There’s a Storm Trooper pun in here somewhere but I can’t for the life of me find it…

    2. Regarding what the slip-rings might be doing on the BB-8, look closely at the video of the red carpet BB-8’s internals in the post above and you’ll see that further outward along the shaft, just past the slip rings are something else with wires going to what may be LEDs for projecting lights to various places on the interior of the ball (at least that’s a theory in the BB-8 Builders Group about what’s on the ends of those wires.) So as the guys said, the slip rings are passing the electrical signals (power in this case) from the stationary middle section to the LEDs on the rotating shaft.
      Here’s a link to a post saying that in the group http://bb8builders.club/forum/showthread.php?1176-Star-Wars-Celebration-Stage-BB-8-Revealed!&p=9730&viewfull=1#post9730 but you’ll probably have to be a member to see it.

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