AQUA: An underwater walking robot

Based on the RHHex hexapod robot, the AQUA robot is an aquatic robot that swims via the motion of its legs, rather than using thrusters and control surfaces for propulsion. Through an appropriate set of gaits, the AQUA vehicle is capable of five-degree-of-freedom motion in the open water, it can swim along the surface and it can walk along the seabed. The vehicle itself is augmented with a variety of sensors that can be used to estimate the robot’s position with respect to local visual features as well as a global frame of reference. Here we describe the basic vehicle design along with some of the sensing and localization projects that are currently underway within the project. Keywords-autonomous robot, aquatic robot, robotic sensing The Site Acquisition and Scene Re-inspection (SASR) task is fundamental to many teleoperated and robotic tasks, including tasks that will take place underwater. A typical scenario in a SASR task is as follows. A robot is deployed near the site. Under operator control or supervision, the robot walks out into the water and is controlled or directed to a particular location on the where sensor measurements are to be made. (This may be the supposed location of some environmental incident, the location of known fish stocks that must be inspected periodically, or some similar task.) Once near the required site, the robot navigates to the selected location, where it utilizes its ability to move to achieve an appropriate pose from which to undertake extensive sensor readings over an extended time period. Once measurements are made, the robot then returns home autonomously. Later, the robot actively guides – and potentially controls – its motion to the previously visited site in order to collect additional data. Solving the SASR task requires solutions to a number of scientific and engineering questions including problems of position and pose estimation in unstructured environments, underwater landmark recognition, robotic navigation, motion control, path planning, vehicle design, environment modeling and scene reconstruction, 3D environment exploration and autonomous and teleoperated control of a robotic vehicle. The SASR task is a formidable task for terrestrial vehicles. It is even more complex in the full 6 degree-offreedom environment found in the aquatic domain. The aquatic domain includes complications related to the increased degree-of-freedom of the task, issues related to station keeping, issues related to sensing, issues related to the differences involved in mobility in open water versus shallow water versus motion along the surface. In this paper we describe the AQUA robot – a six legged underwater walking robot – and some of the results to date in the search for solutions to problems related to SASR.