Transition Gradient from Standing to Traveling Waves for Energy-Efficient Slope Climbing of a Gecko-Inspired Robot

Lateral undulation patterns of a flexible spine, including standing waves, traveling waves, and their transitions, enable agile and versatile locomotion in sprawling animals. Inspired by this, we proposed body-wave transition strategies for energy-efficient inclined-surface climbing of a gecko-inspired robot with a bendable body. Using the robot as a scientific tool, we searched a large space of body movements (i.e., percentage of traveling waves and stride frequency) to explore climbing performance at different slope angles. Consequently, we designed a body-wave strategy to smoothly transition from a standing wave at low speeds to a traveling wave at high speeds to achieve energy-efficient climbing for each slope angle. Through a real robot experiment on the steepest slope (30 degrees), we demonstrated that the robot can reduce energy consumption by 7% compared to climbing with a constant-body movement owing to the transition gradient from standing to traveling waves with an optimal speed. To this end, our study can pave the way for the development of climbing robots that utilize multiple body movement patterns with smooth transitions. Moreover, it can make a valuable contribution to biologists by formulating a novel hypothesis concerning the energy efficiency of gecko climbing.