>>195073Wouldn't surprise me if there was an inertial measurement unit under there, along with GPS. That's how subs navigate (and most commercial aircraft too), three weighted disks at right angles to each other, encoder on the disk, and current measurement on the servo. Knowing the mass and RPM of the disc, and measuring the power required to keep the disc spinning at a certain RPM, you can calculate accelleration in all axes (and therefore position).
Here's the GPS antenna I put up at work for timing.
