1. Underwater Robotic Fish Phase II: Buoyancy P15029 Project Summary The objective of this project is to create an underwater robot that looks and swims like a fish. The fish is to achieve these biomimetics by utilizing McKibben muscles to hydraulically propel the fish. The fish will be able to swim forward and turn, and have depth control using active buoyancy in both R/C and autonomous modes. This project is a continuation of P14029, who built a robotic fish capable of swimming forward and turning. The project was an exercise in biomimicry and used artificial McKibben muscles to propel the robot. Project Summary The objective of this project is to create an underwater robot that looks and swims like a fish. The fish is to achieve these biomimetics by utilizing McKibben muscles to hydraulically propel the fish. The fish will be able to swim forward and turn, and have depth control using active buoyancy in both R/C and autonomous modes. This project is a continuation of P14029, who built a robotic fish capable of swimming forward and turning. The project was an exercise in biomimicry and used artificial McKibben muscles to propel the robot. Acknowledgements Special Thanks Dr. Kathleen Lamkin-Kennard and Rick Lux Mark Schiesser and Triline Automation Dr. Gomes, Dr. Sciremammano, and Dr. Schrlau Previous Team – P14029 Acknowledgements Special Thanks Dr. Kathleen Lamkin-Kennard and Rick Lux Mark Schiesser and Triline Automation Dr. Gomes, Dr. Sciremammano, and Dr. Schrlau Previous Team – P14029 McKibben Style Muscles and Swimming McKibben Style Muscles contract when the tubing expands into its braided sleeving when pressurized. McKibben Style Muscles historically have been used pneumatically – using pressurized air for contraction. However, for the Underwater Robotic Fish, the McKibben Style Muscles are utilized hydraulically, where pressurized water contracts the air muscles. The ends of the McKibben Style Muscles are attached via tensioning cables to joints in the tail. When actuated the muscles pull on those tensioning cables, moving the joints, and producing a swimming motion. The McKibben Style Muscles and tensioning system allow the fish to use its surroundings as a means of propulsion. McKibben Style Muscles and Swimming McKibben Style Muscles contract when the tubing expands into its braided sleeving when pressurized. McKibben Style Muscles historically have been used pneumatically – using pressurized air for contraction. However, for the Underwater Robotic Fish, the McKibben Style Muscles are utilized hydraulically, where pressurized water contracts the air muscles. The ends of the McKibben Style Muscles are attached via tensioning cables to joints in the tail. When actuated the muscles pull on those tensioning cables, moving the joints, and producing a swimming motion. The McKibben Style Muscles and tensioning system allow the fish to use its surroundings as a means of propulsion. Eco-Flex Skin Eco-Flex are platinum-catalyzed silicones that are versatile and extremely easy to mold and use. To produce a more life-like robotic fish, an Eco-Flex sheet was molded to wrap around the tail. The Eco-Flex stretches, moves, and feels like flesh. Over the tail, the Eco-Flex produces the desired aesthetics of a fish. Eco-Flex Skin Eco-Flex are platinum-catalyzed silicones that are versatile and extremely easy to mold and use. To produce a more life-like robotic fish, an Eco-Flex sheet was molded to wrap around the tail. The Eco-Flex stretches, moves, and feels like flesh. Over the tail, the Eco-Flex produces the desired aesthetics of a fish. Buoyancy System The original fish was able to swim only at the surface of the water and subsequently, the customer wanted to include active buoyancy control in this second phase, with the ability to go up and down within a 3ft depth. The 3ft depth was quantified by the depth of the swimming pool available for demonstrations. With this requirement, it was essential to understand the physics behind buoyancy. Buoyancy is the force exerted on an object that is immersed in a fluid. Essentially, the buoyant force on an object is equal to the weight of the fluid it displaces. If the buoyancy force is less than the weight of the object, then the object will sink, called negative buoyancy. If the buoyancy force is greater than the weight of the object, then the object will float, called positive buoyancy. To achieve neutral buoyancy, the buoyant force and weight of the object must be equal. This system is modeled after a ballast tank. The air bubble originally present in the PVC container begins to compress as more and more water fills in. The compressed air and added water increases the weight for the same volume of space, thus forcing the fish to sink in the water. Once released, the compressed air pushes the water back out of the system bringing the fish back to the surface. Actuated McKibben style muscle (top), and relaxed McKibben muscle (bottom) Wireless Communication Communicating wirelessly to the fish underwater presented some unique challenges. Typical close range wireless systems like Wi-Fi and Bluetooth use a transmission frequency of 2.4 GHz. This high of frequency works well in air but is strongly attenuated in water. Our solution was to develop a lower frequency transceiver that operated at 315 MHz. This design aptly accommodated the close range and shallow depth requirements set for the project. To maintain a communication link over farther underwater distances, a more robust system using acoustic transmission would be appropriate. Wireless Communication Communicating wirelessly to the fish underwater presented some unique challenges. Typical close range wireless systems like Wi-Fi and Bluetooth use a transmission frequency of 2.4 GHz. This high of frequency works well in air but is strongly attenuated in water. Our solution was to develop a lower frequency transceiver that operated at 315 MHz. This design aptly accommodated the close range and shallow depth requirements set for the project. To maintain a communication link over farther underwater distances, a more robust system using acoustic transmission would be appropriate. From left to right: Ballast Tank: At neutral buoyancy, submerging, and surfacing. 315 Mhz RF Module Oscilloscope signals for transmitted information (top) and received data (bottom) On-Off Keying (OOK) Modulation Fred CookhouseSarah BaileyChloe BohlmanIgor DrobnjakBrandon MicaleMark Pitonyak Mechanical Engineer Electrical EngineerMechanical EngineerBiomedical EngineerElectrical Engineer Goals and Objectives Design an active buoyancy system Add underwater remote controlling Program an autonomous swim mode Improve physical aesthetics of the fish Original CAD Model of Final Design Phase MSD I