Grey cam of eccentric circular goove is immobile.
Its eccentricity and length of green cranks are equal.
Radius of center circle of the cam groove and radius of yellow crank are equal.
When yellow shaft rotates, the direction of the green cranks is unchanged during rotation.
In fact it is a combination of 6 parallelogram mechanisms.
Orange conrods help in overcoming unstable positions when the green and yellow cranks are in line.
Turn cam to adjust the direction.