[kylebrown]

That must be the purpose of the spherical marker-balls on the "pendulum" (looks like a rod???), two of them dividing it into three segments. I wondered what they were for, I'm guessing they help with the motion capture/tracking.

[chm]

Maybe, but they could also be used to fine-tune the rod's moment of inertia.

[elteto]

They probably use them to track the center of gravity of the rod while in flight.