A ball-shaped underwater robot for direct inspection of nuclear reactors and other water-filled infrastructure

In this paper we present a new type of spherical underwater robot that is completely smooth and uses jets to propel and maneuver. This robot is specifically designed for the direct visual inspection of water-filled infrastructure such as the inside of nuclear powerplants. The unique propulsion architecture consists of a single bidirectional centrifugal pump combined with two fluidic valves. The pump is used to produce a high velocity jet while the valves are used to quickly switch the jet between output ports. The spherical shape means that the robot is simple to model and control, maneuverable, and robust to collisions. The propulsion architecture is described in detail along with a rigid body model for maneuvering control. A novel valve PWM controller is used to achieve heading control, and the controller performance is confirmed with both simulation and experiments. Finally, experiments are used to illustrate the turning and diving performance of the robot.