Morphological Characteristics That Enable Stable and Efficient Walking in Hexapod Robot Driven by Reflex-Based Intra-Limb Coordination

Insects exhibit adaptive walking behavior in an unstructured environment, despite having only an extremely small number of neurons (105 to 106). This suggests that not only the brain nervous system but also properties of the physical body, such as the morphological characteristics, play an essen- tial role in generating such adaptive behavior. Our study aims at investigating the effect of body morphological characteristics on the walking performance in a robot model, which is designed to mimic an insect. To this end, we constructed an insect-like hexapod model in a simulation environment that implements a reflex-based intra-limb coordination control. Herein, for a set of walking parameters, which were optimized to maximize the energy efficiency at the target speed, we investigated the effects of changes in the standard posture of the two leg joints on the walking success rate for various initial conditions and cost of transport (CoT) as an index of energy efficiency. Simulation results indicated that robots with specific mor- phological characteristics similar to those of insects exhibited high gait stability and energetic efficiency. Because only the reflex-based control was employed, the inter-leg coordination occurred spontaneously, suggesting that our approach would lead to a useful design methodology from the perspective of computational cost in generating the walking locomotion.