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The ability to upright quickly and efficiently when overturned on the ground (terrestrial self-righting) is crucial for living organisms and robots. The emerging field of terradynamics seeks to understand how and why different animals use diverse self-righting strategies. We studied this behavior using high speed multiangle video in nymphs of the invasive spotted lanternfly (SLF, Lycorma delicatula), an insect that must frequently recover from falling in its native habitat. While most insect species previously studied can use wing opening to facilitate overturning, nymphs, like most robots, are wingless. SLFs were highly successful at self-righting (>92% of trials) with no significant difference in the time or number of attempts required for three substrates with varying friction and roughness. These nymphs seldom overturned using the pitching and rolling strategies observed for other insect species, instead primarily flipping upright by rotating around a diagonal body axis. To understand these motions, we used video, photogrammetry and Blender rendering software to create novel, highly realistic 3D models of SLF body poses during each strategy. These models were analyzed using the energy landscape theory of self-righting, which posits that animals use methods that minimize energy barriers to overturning, and inertial morphing, which proposes the animal adjusts its body pose to minimize the rotational inertia during overturning, a theory which has not been applied to self-righting. A combination of both theories was found to explain the observed preferred strategies of this species, indicating the value of using 3D renderings with mechanical modeling for terradynamics and biomimetic applications.
The ability to upright quickly and efficiently when overturned on the ground (terrestrial self-righting) is crucial for living organisms and robots. The emerging field of terradynamics seeks to understand how and why different animals use diverse self-righting strategies. We studied this behavior using high speed multiangle video in nymphs of the invasive spotted lanternfly (SLF, Lycorma delicatula), an insect that must frequently recover from falling in its native habitat. While most insect species previously studied can use wing opening to facilitate overturning, nymphs, like most robots, are wingless. SLFs were highly successful at self-righting (>92% of trials) with no significant difference in the time or number of attempts required for three substrates with varying friction and roughness. These nymphs seldom overturned using the pitching and rolling strategies observed for other insect species, instead primarily flipping upright by rotating around a diagonal body axis. To understand these motions, we used video, photogrammetry and Blender rendering software to create novel, highly realistic 3D models of SLF body poses during each strategy. These models were analyzed using the energy landscape theory of self-righting, which posits that animals use methods that minimize energy barriers to overturning, and inertial morphing, which proposes the animal adjusts its body pose to minimize the rotational inertia during overturning, a theory which has not been applied to self-righting. A combination of both theories was found to explain the observed preferred strategies of this species, indicating the value of using 3D renderings with mechanical modeling for terradynamics and biomimetic applications.
The ability to upright quickly and efficiently when overturned on the ground (terrestrial self-righting) is crucial for living organisms and robots. Previous studies have mapped the diverse behaviors used by various animals to self-right on different substrates, and proposed physical models to explain how body morphology can favor specific self-righting methods. However, to our knowledge no studies have quantified and modeled all of an animal's limb motions during these complicated behaviors. Here, we studied terrestrial self-righting by immature invasive spotted lanternflies (Lycorma delicatula), an insect species that must frequently recover from being overturned after jumping and falling in its native habitat. These nymphs self-righted successfully in 92-100% of trials on three substrates with different friction and roughness, with no significant difference in the time or number of attempts required. They accomplished this using three stereotypic sequences of movements. To understand these motions, we combined 3D poses tracked on multi-view high-speed video with articulated 3D models created using photogrammetry and Blender rendering software. The results were used to calculate the mechanical properties (e.g., potential and kinetic energy, angular speed, stability margin, torque, force, etc.) of these insects during righting trials. We used an inverted physical pendulum model (a “template”) to estimate the kinetic energy available in comparison to the increase in potential energy required to flip over. While these insects began righting using primarily quasistatic motions, they also used dynamic leg motions to achieve final tip-over. However, this template did not describe important features of the insect's center of mass trajectory and rotational dynamics, necessitating the use of an “anchor” model comprising the 3D rendered body model and six articulated two-segment legs to model the body's internal degrees of freedom and capture the role of the legs’ contribution to inertial reorientation. This anchor elucidated the sequence of highly coordinated leg movements these insects used for propulsion, adhesion, and inertial reorientation during righting, and how they frequently pivot about a body contact point on the ground to flip upright. In the most frequently used method, diagonal rotation, these motions allowed nymphs to spin their bodies to upright with lower force with a greater stability margin compared to the other less frequently-used methods. We provide a concise overview of necessary background on 3D orientation and rotational dynamics, and the resources required to apply these low-cost modeling methods to other problems in biomechanics.
Animals and robots must self-right on the ground after overturning. Biology research described various strategies and motor patterns in many species. Robotics research devised many strategies. However, we do not well understand how the physical principles of how the need to generate mechanical energy to overcome the potential energy barrier governs behavioral strategies and 3-D body rotations given the morphology. Here I review progress on this which I led studying cockroaches self-righting on level, flat, solid, low-friction ground, by integrating biology experiments, robotic modeling, and physics modeling. Animal experiments using three species (Madagascar hissing, American, and discoid cockroaches) found that ground self-righting is strenuous and often requires multiple attempts to succeed. Two species (American and discoid cockroaches) often self-right dynamically, using kinetic energy to overcome the barrier. All three species use and often stochastically transition across diverse strategies. In these strategies, propelling motions are often accompanied by perturbing motions. All three species often display complex yet stereotyped body rotation. They all roll more in successful attempts than in failed ones, which lowers the barrier, as revealed by a simplistic 3-D potential energy landscape of a rigid body self-righting. Experiments of an initial robot self-righting via rotation about a fixed axis revealed that, the longer and faster appendages push, the more mechanical energy can be gained to overcome the barrier. However, the cockroaches rarely achieve this. To further understand the physical principles of strenuous ground self-righting, we focused on the discoid cockroach's leg-assisted winged self-righting. In this strategy, wings propel against the ground to pitch the body up but are unable to overcome the highest pitch barrier. Meanwhile, legs flail in the air to perturb the body sideways to self-right via rolling. Experiments using a refined robot and an evolving 3-D potential energy landscape revealed that, although wing propelling cannot generate sufficient kinetic energy to overcome the highest pitch barrier, it reduces the barrier to allow small kinetic energy from the perturbing legs to probabilistically overcome the barrier to self-right via rolling. Thus, only by combining propelling and perturbing can self-righting be achieved, when it is so strenuous; this physical constraint leads to the stereotyped body rotation. Finally, multi-body dynamics simulation and template modeling revealed that the animal's substantial randomness in wing and leg motions help it by chance to find good coordination, which accumulates more mechanical energy to overcome the barrier, thus increasing the likelihood of self-righting.
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