This article describes the design, optimization, and performance evaluation of a novel multimode motion robot named SHOALBOT, which with multimode operations depends on only one type of propulsion device and can work flexibly in the amphibious environment including running on beaches, grasslands, seabed, and swimming in the water. Robots that work in water need to minimize the number of drive components to improve reliability and reduce communication pressure, our unique design enables the robot to rely on a kind of propulsion device named propeller-leg to have the ability to run rapidly in the seaside and seabed, and swim with multi-degrees-of-freedom in the water (such a propulsion system contains only four driving elements), and it can make the robot complete more work content and improve its adaptability to the environment. Running is more stable than swimming and will not disturb the animals in the water, but when the robot encounters a high obstacle with a large area coverage, switching the motion mode to the swimming mode can pass directly over obstacles instead of detouring or giving up work, this can improve work efficiency. We analyzed and optimized propeller-leg by simulation combined with the open water test, the propeller-leg's thrust in the water before and after optimization differs by 400% according to the test results. We optimized the minimum difference between the forward and reverse thrust of the propeller-leg to improve the stability of the robot movement process and optimized the difference from 25% to 3%. This article provides sufficient technical details and completeness, and through a series of performance evaluation experiments validated that the SHOALBOT has excellent movement ability in the amphibious environment compared with other published amphibious robots of the same size.

Bionic amphibious robots are the intersection of biology and robotics; they have the advantages of environmental adaptability and maneuverability. An amphibious robot that combines walking and swimming move modes inspired by a crab (Portunus) is presented in this article. The outstanding characteristic of the robot is that its environmental adaptability relies on the bionic multi-modal movement, which is based on two modular bionic swimming legs and six modular walking legs. We designed the biomimetic crab robot based on the biological observation results. The design, analysis, and simulation of its structure and motion parameters are introduced in this paper. The swimming propulsion capability and the walking performance are verified through indoor, pool, and seaside experiments. In conclusion, the designed bionic crab robot provides a platform with practical application capabilities in amphibious environment detection, concealed reconnaissance, and aquaculture.

Amphibious environments formed from sand and water present a formidable challenge to the running motion of field robots, as the mixing of granular media (GM) and water makes the force laws of robotic legs more complicated during robot running. To this end, we extended the granular resistive force theory (RFT) to saturated wet granular media, named saturated granular RFT (SGRFT), which can be suitable for saturated wet sand submerged in water. This method can extend RFT for dry GM to saturated wet granular media (SWGM) by using the method’s velocity and depth coefficient. The force laws of the robotic legs in dry GM and SWGM were tested, compared, and analyzed. The difference in force laws between the two kinds of media, from the sensitivity to speed (10 mm/s~50 mm/s) and depth (0~60 mm), was calculated. More than 70% of the prediction results of the horizontal resistive force using SGRFT have an error of less than 6%. The effectiveness of the SGRFT in legged robots is proved by simulation and testing of three kinds of legs. The difference in force laws when running is proved by the experiments of the robot equipped with the propeller-leg in dry GM and SWGM, which is vital for amphibious robots working in shoal environments (including dry GM and SWGM ground).

Bionic-legged robots draw inspiration from animal locomotion methods and structures, demonstrating the potential to traverse irregular and unstructured environments. The ability of Portunus trituberculatus (Portunus) to run flexibly and quickly in amphibious environments inspires the design of systems and locomotion methods for amphibious robots. This research describes an amphibious crab-like robot based on Portunus and designs a parallel leg mechanism for the robot based on biological observations. The research creates the group and sequential gait commonly used in multiped robots combined with the form of the robot’s leg mechanism arrangement. This research designed the parallel leg mechanism and modeled its dynamics. Utilizing the outcomes of the dynamics modeling, we calculate the force and torque exerted on each joint of the leg mechanism during group gait and sequential gait when the robot is moving with a load. This analysis aims to assess the performance of the robot’s motion. Finally, a series of performance evaluation experiments are conducted on land and underwater, which show that the amphibious crab-like robot has good walking performance. The crab-like robot can perform forward, backward, left, and right walking well using group and sequential gaits. Simultaneously, the crab-like robot showcases faster movement in group gaits and a more substantial load capacity in sequential gaits.