Preliminary research on the thruster assisted crawler system for a deep sea ROV

In order to reduce a tension on a cable, a deep sea ROV is designed to minimize the weight. However, the ROV having a lightweight is apt to wheelie when running by means of a crawler system. In order to run stably in counterpoise the combination of the center of gravity and the center of buoyancy should be in an adequate area called ldquostable areardquo which can be obtained corresponding to the weight and the buoyancy by the theory described in previous papers. The stable area becomes small as the weight is light. The center of gravity and the center of buoyancy is designed to be in the stable area. However, one of the important matters is that the ROV runs forward and also backward. It results in changing the discrimination of the stable area. And it sometimes makes the center of the gravity and the center of buoyancy sometimes to be outside of stable area. So, it is advantageous to increase the weight only when running by crawler system and to change the center of gravity meaningly. This paper proposes a method to virtually increase the weight and to change the center of gravity by using thrusters. And we conducted preliminary experiments using a small-size ROV having four thrusters and crawler system in a water tank to confirm the advantageous effect.