Modeling and Design of a Pigeon-Inspired Robot with Passively Bending Wings

Most traditional ornithopters are equipped with active deformation wings for flight control. However, this inevitably results in redundant actuators and a complex mechanical structure, that reduce flight efficiency. According to the flight data of pigeons (Columba livia), we propose a simple but subtly designed robot that has a passively bending leading-edge spar of the wing and no need for redundant actuators. Accordingly, a double pendulum with a spring system was used to mimic the passive bending of the pigeon's forearm muscles during the upstroke and downstroke. Furthermore, by analyzing the longitudinal flight dynamics, we found that the passive bending of wings increases lift, which relates to flight maneuverability, by changing the effective wing area. Finally, we conducted experiments on wing kinematics, lift/thrust generation, power consumption, and properties of the compliant revolute joint for three springs with different stiffness. The experimental results show that the optimal design of our robot generates a lift of 1.8 times the take-off weight, which is superior to the performance of existing state-of-the-art pigeon-scale ornithopters (wingspan: approx. 600 mm). In addition, its energy consumption is 38.2% lower than that of existing pigeon-scale ornithopters. Moreover, free-flight tests show that the asymmetry bending angle due to the compliant revolute joint effectively improves flight maneuverability.