Foot trajectory planning of frog swimming based on propulsion mechanism

To provide reasonable reference trajectories for frog inspired robot, the bionic trajectory generation was studied in this paper. Though joint trajectories vary with different motion modes, joint speeds are too fast and tuned with the musculoskeletal system. However, mechanical structures of bionic robot are simplified and diver abilities limit the speed, so the method to generate joint trajectories which not only reflect the characteristics of real frog swimming but also are within the limitation of drivers were proposed in this paper. Firstly, swimming mechanism of frog was briefly introduced to analyze motion patterns of hind limbs and webbed feet. Secondly, trajectory (relative to body) planning was divided into hind limb planning and webbed foot planning. Hind limb trajectory planning was conducted via end track planning and acceleration planning, while acceleration planning was operated for webbed foot planning. Then, trajectories could be operated from fast to slow by adjusting duration time of the planned trajectories. Finally, the trajectories were used as input of hydrodynamic simulation to validate the trajectory planning method.