What's the best way to roll?

Now that the static model is kinda working and we proved that he can roll, HOW should he roll?

In "How Do I Make Him Drive" I discussed a few options, however since then another has revealed itself.  If you watch the Star Wars Celebration: Anaheim BB-8 roll-out video closely, you may notice that he pretty much rolls around the same axis the entire time.  That's interesting.  There's another way to make a ball roll.

What I think they did (and pointed out by the BB-8 Builder's Club) is to have a "driveshaft" that runs between two points on the sphere.  That makes him run in a straight line.  To turn, there's a flywheel, likely hanging below the driveshaft as low as possible.  Conservation of Angular Momentum means that when the flywheel is spun rapidly in one direction, the sphere has to rotate in the other direction.  Together the movement is pretty natural.

BB-8 on Stage at Star Wars Celebration Anaheim

The endpoints of his rotation axis appear to be in the middle, or close to the middle of the white "triangles" between what we builders have labeled the 1-2-3 panel rings and the 4-5-6 rings.  (That numbering scheme is a coincidence, I was thinking of dice and the orientation is pure luck, but easy to remember.)

Furthermore, folks had notice an interesting ring on the model where it looks like there's a round access or construction mark.  That ring surrounds the 1-2-3 triangle.  Not sure if it's related to the driveshaft, but seems likely that there's something interesting to cause it.

Ring on Celebration BB-8 Stage Model

So I think what might work best is to have a "driveshaft" between the two triangle panels.  There's a video of model doing this on YouTube.

That technique solves a lot of concerns about my build.  The interior was intended to be smooth to allow a "hamster" to roam, but with a driveshaft it doesn't have to be as particular.  In addition, it allows for simplified wiring and placement of the LEDs... Eventually maybe even room for some of the toys in the hatch panels?

Anyway, that's what I'll investigate in the future.