Violet frame pivots around grey base.

Pink gear to which an antenna is fixed, pivots around the violet frame. Inputs: green and blue gears.

Output: pink gear.

Three small gears are of the same tooth number.

Four yellow gears are identical.

The video shows alternately:

1. When green and blue gears rotate in the same direction and with the same speed, the violet frame is immobile, the pink gear pivots around its own axis.

2. When green and blue gears rotate in opposite directions and with the same speed, the violet frame pivots on its revolute joint with the base, the pink gear does not pivot around its owns axis.

Thus the pink gear has 2 degrees of freedom (rotations).

Advantage: motors are base grounded.

The combination of input velocities or turning angles gives various output motions or positions.