Figure 3: Top of the robot (left) and bottom of the robot (right)
Materials and Methods Overview:
Our robotic starfish consists of a 3D-printed body that houses thirty legs, four servo motors, thirty eyelets, and thirty strings. Rather than attempt to mold the body out of silicone, we decided that the hard 3D printed case would serve applicably as our main goal was to model the motion of the feet(Figure ). In our design, we used four ANNIMOS 20Kg digital servos bought on Amazon. We chose this specific servo because they are cost effective, lightweight and have a 270 degree rotation which is large enough to achieve our desired goals of tensioning the strings. Also, this is a model that we are familiar with using based on prior projects. To do so, we connected each servo motor to one or two legs on each of the five limbs, seven or eight feet per servo total, via a fishing line. The fishing line we chose needed to be able to withstand high tension force. We found the Berkley Trilene Big Game Braid, which is a threaded fishing line, from Walmart which holds up to 65 lbs and has a diameter of 0.015 inches. The fishing line runs from the motor through eyelets before attaching to the 3D-printed feet to orient the force the string creates when the motor turns in the proper direction of motion. Rubber bands were attached opposite the string in order to restore the foot to its upright position while the motor releases tension in the string. The servos operate in two pairs; while two servo motors pull the strings, two release tension, so while half the feet pull the starfish forward, the other half of the feet restore and ready themselves to pull the starfish forward next (Figure ).
Figure 4: Visualization of Servo Operation
Because there are several moving parts, and it is important that we closely examine each in its entirety, we created a section for each part.