Structure Design and Kinematic Modeling of a Robotic Bird Attitude Transformation Mechanism Based on Avian Flight Characteristics

Birds are capable of bidirectional changes in wing morphology, transitioning from folded to extended states or vice versa during takeoff and landing. However, most bird-like robots struggle with wing folding, resulting in poor biomimicry and an inability to meet the attitude requirements for flapping wings in multimodal movements. This paper presents a multi-motor solution with an attitude transformation mechanism based on a crank-rocker structure, enabling the wings to transition between folded and extended states while performing flapping, twisting, sweeping, bending, and their coupled motions. A kinematic model of the mechanism is developed, and the length constraints of the main linkages during key movements are derived. A prototype is designed and tested to evaluate the primary flight attitudes required for both basic and multimodal movements. The test results demonstrate that the attitude transformation mechanism, through coordinated motor operation, can replicate the wing movements of birds during different flight phases, allowing the robotic bird's flapping wings to achieve bird-like flexibility in motion. The key angles of the wing motion were measured using a motion capture system, confirming the accuracy of the kinematic model.