  The concept of aerial-aquatic robots has emerged as an innovative solution
that can operate both in the air and underwater. Previous research on the
design of such robots has been mainly focused on mature technologies such as
fixed-wing and multi-rotor aircraft. Flying fish, a unique aerial-aquatic
animal that can both swim in water and glide over the sea surface, has not been
fully explored as a bionic robot model, especially regarding its motion
patterns with the collapsible pectoral fins. To verify the contribution of the
collapsible wings to the flying fish motion pattern, we have designed a novel
bio-robot with collapsible wings inspired by the flying fish. The bionic
prototype has been successfully designed and fabricated, incorporating
collapsible wings with soft hydraulic actuators, an innovative application of
soft actuators to a micro aquatic-aerial robot. We have analyzed and built a
precise model of dynamics for control, and tested both the soft hydraulic
actuators and detailed aerodynamic coefficients. To further verify the
feasibility of collapsible wings, we conducted simulations in different
situations such as discharge angles, the area of collapsible wings, and the
advantages of using ground effect. The results confirm the control of the
collapsible wings and demonstrate the unique multi-modal motion pattern between
water and air. Overall, our research represents the study of the collapsible
wings in aquatic-aerial robots and significant contributes to the development
of aquatic-aerial robots. The using of the collapsible wings must a
contribution to the future aquatic-aerial robot.
