With a team of four other students, I helped to design and build a mechanical crab toy and then integrate it into a game for fourth grade students. The main focus of the project was to create a fun and engaging game for a specific user group, but we also focused heavily on designing a complex and interesting mechanical system. I primarily focused on the detailed design and fabrication of this part of the project.
To make the crab's legs appear to move as a real crab's do, we used a five bar linkage known as a "Klann Linkage." This linkage takes rotational motion from a hacked hobby servo and creates a non-standard path that both looks and acts more like a crab's step. An animation of this is shown below.
The project was mechanically very successful, with the crab walking and turning without issue. It was also able to climb over the blocks that we used as obstacles in our game, due to the motion of the legs.