Not a mechanical engineer but I think this is what is happening.
Note that Shaft F and shaft D are made to rotate in opposite directions.
Then another gear is made to pit those motions against each other, by means of that wacky rotating frame A.
To see why let’s unwrap it from a polar coordinate to something more linear.
Imagine a wheel with gears resting on a rail with teeth. The wheel has an axle going through it. If you drag the wheel’s axle forward horizontally that’s like what Frame A does to impart 1x rotation. But then the rail is also moving backwards, giving you 2x rotation.
You're entirely correct - it's a modified differential drive.
The two shafts are coaxial to each other and drive their corresponding gears in opposite directions. The frame is fixed relative to one shaft but mobile relative to the other, which is where the extra 1/2 of relative motion comes from.
The traditional way to do this was with a crossed belt. This is the higher-friction lower-slippage version of that.
Note that Shaft F and shaft D are made to rotate in opposite directions.
Then another gear is made to pit those motions against each other, by means of that wacky rotating frame A.
To see why let’s unwrap it from a polar coordinate to something more linear.
Imagine a wheel with gears resting on a rail with teeth. The wheel has an axle going through it. If you drag the wheel’s axle forward horizontally that’s like what Frame A does to impart 1x rotation. But then the rail is also moving backwards, giving you 2x rotation.
I think!