One of the alternative mechanisms I am considering for the rat's arm movement in my new piece is a moving rack assembly. I built a quick mock-up out of a few scraps from around the shop.
The two dowels are to keep the lower piece of the rack moving only in the vertical direction. In the final version I may use brass rods in brass tubes to ensure the piece moves freely and does hang up. Having the rods straight and parallel will be important. The upper piece will move left to right on the rollers to move the arm front to back. Beneath the lower piece is a cam (on the shaft protruding to the front) that lifts both pieces up and down as the shaft turns.
Even with tighter tolerances and different materials, I believe from building this prototype that the whole mechanism would run more smoothly with two identical cams, with roller followers, bearing on either end of the bar.
I will take a quick look a a few other concepts, including a four bar mechanism before deciding on the final mechanism.
Automata is a creative blend of my life interests , engineering, art and woodworking.