In Mechatronics at San Diego State University, I was responsible for designing and fabricating torpedoes. In the International Robo-Sub Competition, one of the challenges requires that the autonomous underwater vehicle (AUV) be able to fire a projectile (torpedo) through a 5 inch by 5 inch square hole on a board from approximately a foot away, at a depth of 10 feet. The dimensions of the torpedo could be no more than 2 inches wide by 6 inches long and it had to weigh less than 2 pounds. It is also important to note that this design had to be compatible with the torpedo holder on the current AUV. Our vehicle’s pneumatic system sends pressurized air at 60 psi to the back of the torpedo to propel it forward. My job was to create a statically and dynamically stable torpedo that would travel in a direct path to the designated target.

 

To fulfill these requirements, I employed an iterative design process. For every iteration, the geometry of the body was symmetric and the center of pressure remained about one body-diameter behind the center of gravity to maintain static stability. However, the infill density, geometry of the fins, and length of the torpedo varied with each iteration so that I could experimentally observe which was most stable. The final design had a non-linear infill density to increase rotational inertia about the center of gravity. However, the design maintained neutral buoyancy, was the full 6 inches in length, and had trapezoidal fins. All the designs were done in SolidWorks and each torpedo was fabricated using an Ultimaker 3-D Printer.