Design for precision multi-directional maneuverability: Egg-shaped underwater robots for infrastructure inspection

In this paper we examine the dynamics of a unique type of jet propelled, spheroidal robot design. This robot uses jets angled inward into a diamond shape to achieve superior planar dynamics. We explore the role of the diamond configuration in avoiding nonminimum phase behavior and we examine the best vehicle aspect ratios for this type of robot design. We use a degree of controllability metric to illustrate the uncontrollable behavior of certain designs and also identify an optimal aspect ratio of 1.4. The paper concludes by incorporating these lessons into a new 5 degree-of-freedom prototype robot that provides substantial improvements over previous designs. This robot uses centrifugal pumps and fluidic valves to achieve high maneuverability and unique motions such as forward and reverse motions, sway translations, and turning in place. In addition, this design can achieve improved forward efficiency through the use of dual output-pumps and can perform these planar motions at various vehicle depths through the use of a closed loop depth control system.