A brittle star-like robot capable of immediately adapting to unexpected physical damage

Abstract

A major challenge in robotic design is enabling robots to immediately adapt to unexpected physical damage. However, conventional robots require considerable time (more than several tens of seconds) for adaptation because the process entails high computational costs. To overcome this problem, we focus on a brittle star—a primitive creature with expendable body parts. Brittle stars, most of which have five flexible arms, occasionally lose some of them and promptly coordinate the remaining arms to escape from predators. We adopted a synthetic approach to elucidate the essential mechanism underlying this resilient locomotion. Specifically, based on behavioural experiments involving brittle stars whose arms were amputated in various ways, we inferred the decentralized control mechanism that self-coordinates the arm motions by constructing a simple mathematical model. We implemented this mechanism in a brittle star-like robot and demonstrated that it adapts to unexpected physical damage within a few seconds by automatically coordinating its undamaged arms similar to brittle stars. Through the above-mentioned process, we found that physical interaction between arms plays an essential role for the resilient inter-arm coordination of brittle stars. This finding will help develop resilient robots that can work in inhospitable environments. Further, it provides insights into the essential mechanism of resilient coordinated motions characteristic of animal locomotion.

Three‐Legged Locomotion and the Constraints on Limb Number: Why Tripeds Don’t Have a Leg to Stand On

“…[115] This design is interesting in that it uses gravity and the inherent instability of the first step to its advantage. [117] This control mechanism has been successfully modeled and replicated in a five-armed robot [118] and this, combined with the behavior observed in living ophiuroids, demonstrates that efficient control and coordination of three legs is certainly possible. The third leg is then lifted and as the robot begins to fall the third leg freely swings forward between the supporting legs like a pendulum before catching the fall on the other side.…”

“…Ophiuroids can quickly and efficiently adjust the coordination of limb movements when they lose one or multiple arms because their decentralized nervous system allows for each arm to be controlled with relative autonomy. [117] This control mechanism has been successfully modeled and replicated in a five-armed robot [118] and this, combined with the behavior observed in living ophiuroids, demonstrates that efficient control and coordination of three legs is certainly possible. Another design, called the trident snake robot, is comprised of a central, triangular body with three radiating arms, each with a passive nonslide wheel.…”

Integrating morphology andin vivoskeletal mobility with digital models to infer function in brittle star arms

“…; Kano et al. ; Matsuzaka et al. ), and ranges of lateral motion in the arms have been measured externally on living specimens (LeClair & LaBarbera, ).…”

Generalized locomotion of brittle stars with a flexible number of arms

“…In past quantitative studies using five-armed brittle stars, antiphase synchronization of two distant arms has been supported by assessing the stop and start timing of arm movements [11] and by evaluating E α β as in our study [12]. This locomotor mode, which is referred to as "breast stroke" or "rowing," is characterized by a leading arm and its side rowing arms [4,5,[7][8][9][10][11][12].…”

“…As typical echinoderms show pentaradial symmetry, most ophiuroid species standardly have five multi-jointed appendages called "arms," which extend from the "disk" at the center. Previous studies have described arm movements in the locomotion of five-armed species in qualitative terms [4][5][6][7][8][9][10] as well as in quantitative terms [11,12]. Several locomotor modes have been known even in a single species.…”