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.

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The article presents a novel flapping wing mechanism for Micro Aerial Vehicle (MAV) inspired by one of the most efficient flyers of the aerial world, the Common swift ( Apus apus). The flight characteristics such as wing beat frequency, wing beat amplitude, and fore and aft movements, as well as wing rotation of the bird at a flight speed 8 m /s, were studied. The common swift rotates its hand wing keeping the pitch of the arm wing constant during the entire wingbeat cycle. The hand wing undergoes forward rotation during the downstroke and backward rotation during the upstroke. This complex wing kinematics enables swift to generate various unsteady aerodynamic mechanisms. Using the geometric and kinematic details, a flapping wing mechanism that emulates the wing kinematics of the bird was designed. The flapping wing mechanism based on the epicyclic ellipsograph mechanism presented herein integrates flapping motion, fore and aft motion, and selective wing rotation. Importantly, this fully constrained mechanism allows performing all the key kinematic motions of the common swift with a single actuator. A kinematic model of the mechanism is presented to calculate the design parameters based on the scale of the MAV. Kinematic simulation of the mechanism is also presented to verify the design.

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In aquatic pedestrian locomotion the dynamics of terrestrial and aquatic environments are coupled. Here we study terrestrial running and aquatic punting locomotion of the marine-living crab Pachygrapsus marmoratus. We detected both active and passive phases of running and punting through the observation of crab locomotory behaviour in standardized settings and by three-dimensional kinematic analysis of its dynamic gaits using high-speed video cameras. Variations in different stride parameters were studied and compared. The comparison was done based on the dimensionless parameter the Froude number (Fr) to account for the effect of buoyancy and size variability among the crabs. The underwater spring-loaded inverted pendulum (USLIP) model better fitted the dynamics of aquatic punting. USLIP takes account of the damping effect of the aquatic environment, a variable not considered by the spring-loaded inverted pendulum (SLIP) model in reduced gravity. Our results highlight the underlying principles of aquatic terrestrial locomotion by comparing it with terrestrial locomotion. Comparing punting with running, we show and increased stride period, decreased duty cycle and orientation of the carapace more inclined with the horizontal plane, indicating the significance of fluid forces on the dynamics due to the aquatic environment. Moreover, we discovered periodicity in punting locomotion of crabs and two different gaits, namely, long-flight punting and short-flight punting, distinguished by both footfall patterns and kinematic parameters. The generic fundamental model which belongs to all animals performing both terrestrial and aquatic legged locomotion has implications for control strategies, evolution and translation to robotic artefacts.

Landing on vertical surfaces in challenging environments is a critical ability for multimodal robots—it allows the robot to hold position above the ground without expending energy to hover. Asian flat‐tailed geckos (Hemidactylus platyurus) are observed to glide and perch on vertical surfaces by relying on their tail and body morphology, potentially reducing the control effort to perch. This novel perching mechanism using a bioinspired physical model is discussed and its tail and body parameters to determine their influence on perching success and the kinematics of the gecko's dynamic landing maneuver are adjusted. Perching performance is evaluated by changing the model's torso and tail stiffness. Combining a compliant torso and stiff tail enables the model to passively perch on a vertical substrate with a success rate >90%, compared with ≈10% without a tail attached. A compliant torso is necessary to absorb the in‐flight kinetic energy and accommodate the uncertainties in approach conditions. Similar to the gecko's perching strategy, the stiff tail pushes against the substrate, preventing the model from falling backward head over heels. These findings highlight the critical role of tail and material stiffness for perching and provide a simplified mechanism to impart perching capabilities in robots.

Studies invoking biomitetics have gained significant popularity over the last two decades, allowing for the construction of more lifelike robots inspired by nature. The goal of bioinspired robotics is often twofold: understanding nature's fundamental processes and acquiring the capacity to replicate those processes to ultimately construct improved robotic platforms with similar capability. By examining the underlying principles of locomotion strategies found in nature, researchers sought to develop robots with similar capabilities in aerial, [1,2] aquatic, [3][4][5][6][7][8] and terrestrial [9][10][11][12] environments as well as using the robots as platforms in biomechanics research to understand the fundamentals of animal locomotion. [13] To negotiate compelx environments and flow regimes, animals must be able to perform multimodal locomotion. Highly maneuverable multimodal locomotion is needed for diverse survival needs such as fast escape from predators, quick pursuit, searching for food, breeding, nesting, preserving energy, and migration. [14] The most delicate aspect of multimodal locomotion is the challenging transition from one mode to another at the intersection land-air, water-air, or water-land. Flying and gliding animals transition from air to land by perching on a diverse range of complex, natural, and surfaces. [15] From large birds to microscopic insects, animals rely mostly on passive mechanisms to perch. Birds decelerate in the air utilizing their morphing wings and tail and then land slowly in a controlled fashion as they approach the substrate. During landing, they bend their legs, resulting in a tendon on the ankle's backside to naturally force the toes to grip around a branch. This passively operated mechanism is critical for perching without active gripping control. [16,17] Smaller animals also depend on the functional morphology to increase robustness and reduce neural control effort honeybees use the swinging motion of their abdomen to dissipate residual flying energy to achieve a smooth, stable, and quick landing. [18] Houseflies perch by using their compliant legs to dissipate the high kinetic energy of flight. [19] Perching is not limited to flight animals. Gliding animals in the absence of thrust generation capabilities can also modify their body orientation and body shape to successfully perch. [20][21][22][23] Gliding mammals and flying lizards possess well-defined aerodynamic surfaces allowing them to significantly decelerate their descent and control their body orientation before perching. [24]

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