Insect-machine hybrid robot: Insect walking control by sequential electrical stimulation of leg muscles

This paper reports motion control of living insect legs by electrically stimulating multiple leg muscles under pre-programmed sequential schedule. A living beetle (Coleopteran, Mecynorrhina torquata) was employed as the insect platform. Firstly, we investigated the sequence of leg motions (walking gait) of free-walking beetles to preliminarily understand which motions (leg muscles) are being activated at which timings and for how long. Each beetle leg has three degrees of freedom (DoFs), namely protraction/retraction, levation/depression, and extension/flexion. We then anatomically mapped out and located the leg muscle groups corresponding to each DoF to determine the stimulation sites (electrode implantation sites) for activating our desired leg motions. Silver thin wires were implanted into the muscles and the other ends of the wires were connected to output sites controlled by a microcontroller which allows for the pre-programmed sequential electrical stimulation. Based on the leg motion sequence in the free walking beetles, two types of walking gaits control, namely tripod and galloping were successfully demonstrated. The step frequency, which corresponds to walking speed, is user-adjustable by changing the duration of each stimulation sequence.