Students Build Submarine to Track Octopuses

Marine biologists want to find out more about the Giant Pacific Octopus, but this elusive creature doesn’t willingly reveal its secrets.

Divers can follow the octopus for short periods, but what’s really needed is an undersea robot that will wait patiently outside the creature’s den, ready to shadow its every move. UA engineering undergrads, in collaboration with students from two other universities, are building a mini-sub to answer this need. In July, they took a prototype to Alaska for testing. Appropriately named Shadow III (and painted a bright yellow that belies its sleuthy assignment) the mini-sub includes a video camera and hydrophones (sonar mikes) to track its prey.

Marine biologists, directed by Professor David Scheel at Alaska Pacific University, will use the sub to track octopuses. Meanwhile, undergrads at Colorado School of Mines are developing the hydrophones under the direction of Tyrone Vincent, an associate professor of electrical engineering. The hydrophones are set up to create bi-aural hearing that will allow researchers to determine the direction from which a sound originates.

During the July test, Shadow III completed ten dives in Prince William Sound, with a communications cable linking it to a mother boat on the surface. Divers checked it for leaks, while UA Professor Emeritus Tom Vincent and UA Mechanical Engineering senior Patrick Haley tested its robotic vision, motors and internal computer. Along the way, it encountered and filmed a Giant Pacific Octopus.

Tests included both: Fun and Frustration

“There were some fun moments and some frustrating ones during the testing,” UA’s Vincent said. “We never thought we would have to take the dome off and expose the computer parts to salt air, but, of course, we immediately blew some fuses and had to remove the dome. So we had all this moist, salty air getting into everything.” Lesson learned. Students will repackage all the electronics inside the sub to protect it from salt air when Shadow inevitably has to be adjusted on-site.

Repackaging the computer parts will be the latest in a long list of modifications and redesigns that began with Shadow I in 1998. Shadow has become an annual senior design project in UA’s Mechanical Engineering Department, and is entirely designed and built by undergraduates, with the exception of some computer programming done by a graduate student a couple of years ago.

The project received NSF funding in 2000 and has made great progress since then. Vincent anticipates that it will be ready to track octopuses next year. Before that happens, this year’s student design team will build a wireless communications system to free Shadow from the mother boat. Currently the sub and a computer on the mother boat are linked by a 100-foot-long coaxial cable. “We want to get rid of that tether from the boat and have it come to the surface at a buoy,” Vincent said. “Then there will be a wireless link between the buoy and the boat.”

The team also will modify Shadow’s buoyancy system. Water flows into a ballast ring that circles the center of the sub. The amount of water that it takes on determines the sub’s buoyancy, allowing it to submerge to any depth. Compressed air tanks on the sides of the sub blow this water out to bring Shadow to the surface. “Right now the buoyancy system is under manual control, but we hope to have it under automatic control next time,” Vincent said. “We’ll just type in the depth we want on the computer and Shadow will automatically submerge to that depth.”

SUB will be operational next year

Although the submarine will begin shadowing octopuses next year, Vincent has plenty of ideas to keep senior design teams busy for a long time. “The way it is now, we’ll still be on the surface watching images from Shadow’s video camera and waiting for something to happen,” Vincent said. “We’ll manually control the video camera. But farther in the future we hope to make it totally autonomous.”

In autonomous mode, the submarine would operate on its own, following an octopus using its hydrophone sensors. It would decide when to turn on its video camera, transmitting video to a remote receiver. “This would require the submarine to know something about the topography of the ocean bottom in its area so it wouldn’t run into a big rock or other obstacle while following the octopus,” Vincent said.

The advantage of fully autonomous tracking is that octopuses spend a lot of time in their dens vegging out, which is pretty boring for researchers. Instead of waiting for hours on the surface, biologists could set up the robot to wait quietly for an octopus to emerge from its den. Then the submarine could become their eyes and ears underwater, recording the octopus’ movements for later retrieval. With that goal in mind, Vincent figures there’s plenty of engineering work to keep senior design teams occupied for several years to come.