Bioinspired underwater legged robot for seabed exploration with low environmental disturbance

Abstract

Robots have the potential to assist and complement humans in the study and exploration of extreme and hostile environments. For example, valuable scientific data have been collected with the aid of propeller-driven autonomous and remotely operated vehicles in underwater operations. However, because of their nature as swimmers, such robots are limited when closer interaction with the environment is required. Here, we report a bioinspired underwater legged robot, called SILVER2, that implements locomotion modalities inspired by benthic animals (organisms that harness the interaction with the seabed to move; for example, octopi and crabs). Our robot can traverse irregular terrains, interact delicately with the environment, approach targets safely and precisely, and hold position passively and silently. The capabilities of our robot were validated through a series of field missions in real sea conditions in a depth range between 0.5 and 12 meters.

A Minimal Metric for the Characterization of Acoustic Noise Emitted by Underwater Vehicles

“…Such features make ULR complementary to ROVs and a viable option to solve the trade-off often faced by marine biologists between a highly mobile, yet often noisy ROV and a very silent yet still lander platform [34]. The intuition about low noise signature of ULRs anticipated in Reference [25] was confirmed by the indicators proposed in this work with SILVER2 presenting the lowest NE and f RO among the robots tested.…”

“…Currently, ROVs are the only commercially available option for teleoperated underwater robotic operations. In addition, ULRs, among which SILVER2 is one of the most recent representatives, are capable of moving directly onto the seabed and coupling very good passive station keeping performance with relatively agile mobility [25]. Such features make ULR complementary to ROVs and a viable option to solve the trade-off often faced by marine biologists between a highly mobile, yet often noisy ROV and a very silent yet still lander platform [34].…”

“…The SILVER2 is characterized by six legs 63 cm long, actuated by 18 Dynamixel servomotors controlled using user-tunable feed-forward strategies. As thoroughly described in Reference [25], SILVER2 is capable of hopping on the seabed by means of periodic extensions and retractions of the springy legs and of walking with each leg following a predefined path.…”

“…We performed our analysis on the recordings obtained from two robots belonging to the ROV class, which, at the time of writing, was the only commercially available option for remotely operated explorations by means of robotic devices. We compared the results with a recently introduced Underwater Legged Robot (ULR) [25] that represents a complementary approach to underwater operations [26,27]. Based on the analysis performed and accounting for the simplicity of the recording setup, we proposed two indicators to provide an intuitive and easily obtainable description of the noise signature of underwater robots, i.e., the spectral roll-off point, f RO [28], and the noise introduced to the environment, NE.…”

Learning to stop: a unifying principle for legged locomotion in varying environments

“…However, significant changes in the dynamics of the latter are difficult to explain by the SLIP model alone and, indeed, animals employ a slightly different gait in the underwater environment, which is referred to as punting [8]. An extension of the SLIP model, called underwater SLIP (USLIP, [9]), which takes into account the non-conservative nature of the system, the buoyancy, drag, and added mass effects of the punting gait, captures the dynamic of such locomotion [10], and it is successfully employed as a reference for the locomotion of underwater robots [11,12].…”