A Soft Amphibious Turtle Robot with Flexibility and Omnidirectional Motion Ability Actuated by Multiple Bionic Muscles

Amphibious robots have great application potential in many unstructured task scenarios, such as environmental monitoring, resource exploration, and maritime rescue, due to their cross-medium movement capabilities and adaptability to multiple environments. As a typical representative of amphibians, sea turtles can not only crawl on land but also have excellent underwater movement ability, which is an important source of inspiration for amphibious bionic robots. However, due to a lack of high-performance soft actuators, suitable bionic structure designs, and effective control methods, most of the current bionic turtle robots actuated by smart materials can only demonstrate movement in a single medium (e.g., swimming in water or crawling on land). Here, an amphibious turtle robot actuated by bionic muscles that can achieve effective movements in two media was designed. To enhance the amphibious ability of the turtle robot, a cylindrical dielectric elastomer actuator that can adapt to a variety of environments is designed with a maximum bidirectional deformation (±65°) and a high output force (∼80 mN). By optimizing the motion trajectory of the fins and programming the phase control of multiple bionic muscles, the robot's maximum swimming speed reaches 0.4 BL/s. In addition, the robot can realize different motion modes, such as forward, backward, lateral movement, turning, and crawling. Finally, the high mobility and environmental adaptability of the turtle robot are demonstrated in an L-shaped swimming passage and in two mediums (transition from land to water). This work not only improves the motion ability of bionic amphibious robots but is also useful for the motion control of other bionic robots with multiple actuators.