Even though Aqua's compact size and amphibious locomotion make it ideal for operating around coral reefs, some of our collaborators have other ideas for the robot. They believe Aqua could serve as the basis for other robotic machines that could do environmental inspections in deep water or near shorelines; perform routine monitoring in aquaculture tanks used to raise sea creatures; and also help human divers with predive safety checks and physical tasks underwater.

This past January, the Aqua team emerged from its laboratories in frigid Canada and headed south to sunny Barbados, where McGill University maintains its Bellairs Research Institute. In the months leading up to the January sea trial, our team had exhaustively experimented with the robot in the lab and in test tanks. But how would Aqua function, we wondered, in the uncontrolled conditions of the open sea?

This would be the third field test for the Aqua project, which began in 2004 with funding from the Natural Sciences and Engineering Research Council of Canada and the Institute for Robotics and Intelligent Systems, both in Ottawa. Since that time, Aqua's hull and systems had evolved significantly, as we made its shell more pressure resistant, expanded its repertoire of amphibious gaits, and added enhanced vision hardware [see diagram, “Aqua's Anatomy”]. The newest model consists of an aluminum shell encasing two compact, off-the-shelf PC/104 computer modules: one for vision, the other for overall control of the robot.

A pair of lithium-ion rechargeable batteries powers all of the robot's circuitry, including six independent DC motors, one for each flipper. We used plastic, aluminum, and rubber to fabricate appendages in a variety of sizes and shapes. For example, one set works like a dolphin's flippers, while another functions more like a cockroach's legs. With such insect-inspired limbs, Aqua can walk and even run with surprising agility [see photo, “Taking a Stroll,” and photos below]. It inherited its land prowess from a predecessor, RHex, a six-legged walking robot developed by U.S. and Canadian researchers in a program sponsored by the U.S. Defense Advanced Research Projects Agency. Eventually we hope to develop an appendage design that works well for both walking and swimming.

Aqua carries three video cameras: two looking forward and one back. When the robot is being piloted remotely, the video is sent via a thin fiber-optic tether back to a boat, where a human operator can control the robot's movements with a joystick. Alternatively, the robot can use the visual information to home in autonomously on targets such as a scuba tank or brightly colored objects, a robotic behavior known as “visual servoing.” Aqua is also capable of some intermediate forms of interaction. For example, an operator on the boat may be piloting Aqua while at the same time the robot makes some of its own decisions and responds to a diver's visual cues.

The day before our departure in January, a problem cropped up with Aqua's computer systems. Under certain conditions, when the recently upgraded vision module was activated, the control module would crash. For Ph.D. student Junaed Sattar, this was especially unwelcome news. The experiments Sattar had planned for Barbados used the vision system to evaluate the robot's ability to autonomously track objects underwater. The problem meant that other scheduled experiments relying on vision might have to be canceled as well. After a late night in the lab, the group suspected something was wrong with the power supply feeding the vision and control modules, so a temporary fix was simply to increase the voltage to both.

Then, laden with six enormous watertight cases jammed with laptops, computer screens, cables, cameras, dive gear, underwater camera housings, and, of course, our little yellow robot, our group headed for Barbados. For the initial set of sea trials, we used a room at the Bellairs facility's main building and a ramshackle old beach house as our makeshift labs. We spent the first morning testing the walking gaits of the robot on the sand, putting it into the water to ensure it did not leak, checking the movement of the flippers, and proceeding with some of the locomotion experiments.

Idyllic as it may sound, working with expensive electronics on sandy beaches and in seawater is not easy. Even the simplest test demands exhaustive preparation to ensure that the circuits won't be damaged by the corrosive salt water; the robot doesn't get pummeled by rough currents, tides, and surf; and the researchers don't injure themselves while balancing in the boat or scuba diving with the robot. Field-testing a robot in Barbados, in other words, is not all fun in the sun.