Propelling and perturbing appendages together facilitate strenuous ground self-righting.

Ratan Othayoth,Chen Li

doi:10.7554/elife.60233

Abstract

Terrestrial animals must self-right when overturned on the ground, but this locomotor task is strenuous. To do so, the discoid cockroach often pushes its wings against the ground to begin a somersault which rarely succeeds. As it repeatedly attempts this, the animal probabilistically rolls to the side to self-right. During winged self-righting, the animal flails its legs vigorously. Here, we studied whether wing opening and leg flailing together facilitate strenuous ground self-righting. Adding mass to increase hind leg flailing kinetic energy increased the animal's self-righting probability. We then developed a robot with similar strenuous self-righting behavior and used it as a physical model for systematic experiments. The robot's self-righting probability increased with wing opening and leg flailing amplitudes. A potential energy landscape model revealed that, although wing opening did not generate sufficient kinetic energy to overcome the high pitch potential energy barrier to somersault, it reduced the barrier for rolling, facilitating the small kinetic energy from leg flailing to probabilistically overcome it to self-right. The model also revealed that the stereotyped body motion during self-righting emerged from physical interaction of the body and appendages with the ground. Our work demonstrated the usefulness of potential energy landscape for modeling self-righting transitions.

Highlights

Ground self-righting is a critical locomotor capability that animals must have to survive
These, combined with the fact that previous studies observed minimal proprioceptive sensory input from legs during flailing (Camhi, 1977; Delcomyn, 1987; Zill, 1986), indicate that leg flailing was more feedforward-driven than a feedback-controlled reflex coordinated with wing opening (Figure 3—figure supplement 1)
The roll barrier was lowered to a similar level as the average roll kinetic energy (Figure 7C, solid curve vs. dashed red line). This explained why the modified animal, with its higher average kinetic energy, self-righted at a higher probability than the intact animal (Figure 7—figure supplement 1 solid vs. dashed lines). These findings demonstrated that, even though wing opening did not generate sufficient kinetic energy to self-right by pitching (Figure 7C), it reduced the roll barrier so that self-righting became possible using small, perturbing roll kinetic energy from leg flailing

Summary

Introduction

Ground self-righting is a critical locomotor capability that animals must have to survive (for a review, see Li et al, 2019). It is crucial for animals to be able to self-right at a high probability because it can mean the difference between life and death. To self-right, cockroaches must overcome potential energy barriers seven times greater than the mechanical energy required per stride for steady-state, medium speed running (eight body lengths sÀ1) (Kram et al, 1997) or, exert ground reaction forces eight times greater than that during steady-state medium speed running (five body lengths sÀ1) (Full et al, 1995). Animals struggle to self-right quickly and needs multiple attempts (Brackenbury, 1990; Domokos and Varkonyi, 2008; Full et al, 1995; Hoffman, 1980; Koppanyi and Kleitman, 1927; Li et al, 2019; Silvey, 1973) to self-right due to constraints from morphology, actuation, and the terrain (Domokos and Varkonyi, 2008; Faisal and Matheson, 2001; Golubovicet al., 2017; Golubovicet al., 2013; Li et al, 2019; Steyermark and Spotila, 2001)

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