Figure 5: Original Prototype (left) and Final Prototype (right)
Figure 6: CAD Drawing of Final Body Design at 1/4 Scale
Rather than mold a piece of silicone to act as a more accurate imitation of a starfish, we opted to focus entirely on movement, and thus a 3D printed solid piece that would house the strings and electronics would suffice. The body is made of ABS plastic and was printed on the Stratasys 3D printer in the Washington and Lee University IQ center. The original design had fifty holes equally spaced across each starfish leg for feet (Figure [5], left). However, with spacing concerns for both the strings and eyelets that would control the strings, we opted to reduce this number to thirty. This first design was also too long across that it wouldn’t fit on the Stratasys printing tray so we had to shrink our body size as a whole. The final iteration of the body also included slots rather than round holes to allow the feet to move to their full range of motion (Figure [5], right). We selected a reasonable size for the slots that would allow for six feet per leg and space for the eye screws. This dimension was not calculated, but we catered the rest of the foot design to it to save print material. The feet required less material than the body and we could print more variations for testing quicker. The center of the body was a circular design sized to house four servo motors, with batteries and electronics placed on top. Slot and body dimensions can be seen in Figure [6]. The total distance across from foot to foot is 9.436 inches. This just fit in our 10” by 10” Stratasys printing tray. As we did not plan to place this body in any water, the top of the starfish was left open. This does not imitate a biological starfish, but the choice was made to prioritize locomotion and easy access to mechanical and electrical systems over the cosmetics of the robot.
