A template model reveals self-righting mechanism of a winged robot

Animals and robots must self-right after flipping-over on the ground. Winged insects like many cockroaches push wings against the ground while flailing legs to generate lateral perturbation to self-right. Our previous study of a cockroach-inspired robot revealed the importance of good coordination (measured by phase) between wing pushing and leg flailing. Here, we elucidate the mechanism of phase dependence by developing a template model, validated against multi-body dynamics simulation. The model consists of a point mass body rotating in the sagittal plane, two massless wings, and a flailing leg with a point mass at its end. With modest wing opening and leg flailing, the model struggled to self-right, and successful righting relied on good coordination of the wings and leg. We used the model to calculate the potential energy barrier the body must overcome, mechanical energy input by the wings and leg, and energy dissipation due to collision and friction. With good phases, mechanical energy accumulation exceeded potential energy barrier; with bad phases, it did not do so. We used the template model to predict an optimal coordination strategy to increase self-righting probability. Our study highlighted the importance of appendage coordination in strenuous locomotor transitions.