We had originally hoped to explore the sinusoidal movement pattern of the starfish through the incorporation of their key physiological features in our design. While we did achieve movement in some of the feet, our goal was to achieve motion from all the feet to allow our robot to move unidirectionally. Throughout the design process we came across multiple limitations that made this process more difficult than we had originally anticipated.
The first problem we encountered when it came to the testing phase was the free movement of the legs within the slots. The width of the slots enabled the legs to rotate causing them to become positioned in different directions so that if movement was achieved in all the legs, they would not be moving in the same direction. The length of the slots also caused issues which was why the application of the black tape was necessary to hold the legs in place. Future designs should look at preventing this rotational movement, possibly through smaller leg slots or pin jointed legs. Another limitation that we feel was one of the more prominent issues was the stringing of the system. The way in which the string was attached to the legs caused the string to pull the legs in multiple directions, rather than the unidirectional movement that we had hoped for. By keeping the strings aligned in the same direction, the motor would be able to pull the legs more uniformly. This could be achieved through stringing in a more strict manner. Some ideas to achieve this would be to optimize the layout of the middle of the starfish, precisely calculate where each eye screw should be exactly positioned, and by ensuring that each leg receives the same amount of tension and slack from the strings by regulating the string lengths. The final major limitation we encountered was the material used to allow the feet to grip to the ground surface. This added friction from the sticky fashion tape was too strong for the motors to overcome. Therefore, future designs should explore a different material that would provide enough grip without making movement impossible.
We tested the body on a flat desk surface while the fashion tape was still freshly applied. The friction force of the tape was calculated against a smooth metal surface. Depending on the type of surface that is used for testing, we would expect differences in the results. The friction force would likely be lower on a sandpaper-like material or carpet floor. The lower the friction force, the faster we expect our starfish to move. Ideally, we would want our whole robot to be able to move on a wet sand-like material to mimic that of a real starfish.