Study on Self-Takeoff of a Flapping Robot without Running: Influence of the Initial Pitch Angle on the Takeoff Trajectory

Recently, research on flapping robots inspired by the behavior of insects and birds has become a focus of attention in the fields of robotics and biomimetics. However, most flapping robots require an operator or an assistance device to take off. The goal of this study was to develop a flapping robot that can achieve self-takeoff without running and can be used like a drone. This paper describes the development and evaluation of the flapping robot developed with this aim. The developed robot can generate a thrust that exceeds its own weight with a simple flapping mechanism and a lightweight design. The airspeed was simulated using the thrust measured with a force sensor and the resistance coefficient estimated in a gliding experiment, and it was found to exceed the minimum airspeed required to achieve takeoff 0.3 s from the onset of flapping. The result of the takeoff experiment demonstrated that takeoff was possible if the initial pitch angle was high. However, the pitch angle decreased immediately after takeoff due to the pitching moment generated by the flapping motion. The moment on the tail wing was not enough for the robot to maintain a horizontal posture at low airspeeds during takeoff. It was concluded that the robot requires a control mechanism for the pitching moment generated by the flapping motion and/or accelerators that function without flapping during takeoff, such as hind limbs. Therefore, the parameters required for the design of actuated hind limbs were estimated.