Violet bucket is pivoted on a chain link. Its pin slides in a closed groove G that is equidistant to the locus of the chain link axes A.
Distance between G and A is shorter than distance between two pins of the violet bucket.
The bucket turns 180 deg. at both ends of the chain drive.
The same action is can be got if the bucket without pins is fixed to the chain link, however the bucket is easier to be shaken during motion.