Terrestrial cyborg insects are biohybrid systems integrating living insects as mobile platforms. The insects' locomotion is controlled by the electrical stimulation of their sensory, muscular, or neural systems, in which continuous pulse trains are usually chosen as the stimulation waveform. Although this waveform is easy to generate and can elicit graded responses from the insects, its locomotion control efficiency has not been consistent among existing literature. This study demonstrates an improvement in locomotion control by using a new stimulation protocol, named Burst Stimulation, to stimulate a cyborg beetle's antennae (Zophobas morio). Modulating the continuous pulse train into multiple bursts enhanced the beetle's turning responses. At the same stimulation intensity (amplitude, pulse width, and active duration), the Burst Stimulation improved the turning angle by up to 50% compared to the continuous waveform. Moreover, the beetle's graded response was preserved. Increasing the stimulation frequency from 10 Hz to 40 Hz raised the turning rate by 40 deg/s. In addition, the initial implementation of this protocol in the feedback control-based navigation achieved a success rate of 81%, suggesting its potential use to optimize further the autonomous navigation of terrestrial cyborg insects.

Unlike biomimetic methods, the insect–computer hybrid is an alternative approach to developing insect-scale robots. Insect–computer hybrid is a technique that transforms a living insect into a controllable robot by embedding it with artificial devices. In this article, a beetle (Mecynorrhina torquata) was transformed into a hybrid flying system by mounting an electronic backpack and implanting electrodes on it. Wing trajectories during fictive flight climbing and flight diving were captured to investigate the natural flight-height control of beetles. Compare with the electrically induced wing trajectories via basalar, subalar, and third axillary (3Ax) muscle stimulations, we hypothesized that the basalar muscles are involved in ascending flight, whereas the 3Ax muscles function to reduce the flight-height. By reproducing the electrical stimulations on bilateral muscle pairs during free flights, we found that stimulations of the basalar muscle pair increased vertical accelerations. In contrast, the 3Ax muscle pair's stimulation decreased vertical accelerations gradually as a function of the electrical stimulation frequency. Accordingly, a proportional-derivative feedback controller was proposed to maintain the beetles' flight-height using frequency-dependent electrical pulses on the basalar and 3Ax muscles. In this article, the altitude control of a free-flying beetle was demonstrated for the first time.

This paper demonstrates that our developed beetle-computer hybrid legged robot achieves backward walk, which is impossible by intact beetles themselves in nature. Judging from the curvature of the natural leg spine, we hypothesized that the natural spine has an anisotropic function: the natural spine would provide foot traction only in forward walk but not in backward. The hypothesis was verified as beetles hardly walk backward due to often slips. We then designed an artificial leg spine, which isotropically functions in walk: the foot traction was increased and slipless walk was achieved in both backward and forward walk with the artificial spines being implanted into the beetle legs. For these investigations, a wireless communication device, or “backpack,” was mounted and wired to a live beetle for electrically stimulating leg muscles to remotely modulate leg motions and to perform the forward and backward walk on demand. Overall, the beetle hybrid robot revealed the anisotropic function of the natural leg spine and also achieved the backward walk, which the intact beetle cannot intrinsically perform.

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.

In the original demonstration of insect flight control [2,4], flight initiation, cessation and elevation control were accomplished through neural stimulus of the brain which elicited, suppressed or modulated wing oscillation. Turns were triggered through the direct muscular stimulus of either of the basalar muscles. We characterized the response times, success rates, and free-flight trajectories elicited by our neural control systems in remotely controlled beetles.