For this assignment, we were tasked with actuating a linear to rotary motion mechanism. Starting with a simple scotch yoke, I actuated a pair of pupils to look around the room.

The design is a sleek, open box composed of several layers from which a pair of roving eyes peek out. The first layer provides a window through which to experience the motion, while the second is etched with an original illustration. Behind these is a scotch yoke system which uses a servo to move the pupils around the eye socket opening, with intermittent pauses. Because the servo cycle interacts with the continuous cycle of the scotch yoke, the eyes seem to pause randomly (though of course this is just a larger, slower loop) — sometimes stopping to stare straight at the viewer, or to instead glance to the side.

For this project, the first step was creating a robust scotch yoke mechanism, in order to focus on perfecting the details of the rotary to linear motion.

After testing the motion with a flat laser cut sketch, I doubled up the gears to be made out of two pieces of wood. For the yoke gear, a larger hole in the top facing gear is inset with a collar. This lets the gear spin around the collar while still attaching firmly to the dowel. The handle gear uses the same mechanism. In addition, the handle spins around its own axis using the same inset collar in the bottom facing gear. It took some fiddling to get the both gears turning smoothly with the yoke, but in the end (and with a bit of sanding) the mechanism worked quite well! 

With the knowledge from the scotch yoke test, I then applied a miniaturized version of the mechanism to a much more interesting output. The mechanism was recreated to mount vertically and placed snuggly atop a servo motor. On top of this, I slotted the next two layers, distancing the window layer from the eye sockets so as to create a compelling shadow. Because the full usually box sits bellow eye level, it next took several iterations to account for multiple angles of observation, to be sure there were no visible gaps between layers.

To improve upon this project, I would tighten the tolerances of the guards around the yoke itself. As soon as I turned the project vertically, the play within the mechanism made for a slightly bumpy motion of the pupils, where the yoke isn’t able to stay perfectly level as it moves. Instead, it jumps a bit toward the end of the cycle. I hope to fix this by re-cutting the middle yoke plate with better spaced holes for the dowels.