Mechanical diffraction reveals the role of passive dynamics in a slithering snake

Schiebel, Perrin; Rieser, Jennifer M.; Hubbard, Alexander; Chen, Lillian; Rocklin, D. Zeb; Goldman, Daniel I.

doi:10.1073/pnas.1808675116

Cited by 52 publications

(51 citation statements)

References 39 publications

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“…Previous work found that generalist snakes chose self-deformations in response to available environmental forces [6, 27], a strategy which we might expect would be useful on challenging, deformable materials like GM. However, we previously found evidence that C. occipitalis does not change its waveform when faced with changes to the surroundings [29] and our robot was executing predetermined waveforms. The ability to sense and respond to induced changes in the substrate is apparently unnecessary given the initial selection of an appropriate pattern of self-deformation.…”

Section: Discussionmentioning

confidence: 99%

“…We used nine individuals collected from the desert in Arizona, USA (Appendix B). These sand-specialists are a consummate example of a successful strategy for moving across material with memory; they use a stereotyped waveform ([21], [29]) to quickly traverse many body lengths across the sand with little slipping of the body, leaving behind distinct tracks [31].…”

Section: Performance Of Limbless Locomotors On Granular Materialsmentioning

confidence: 99%

“…Better understanding of the connection between body self-deformations, substrate remodeling and force generation, and the resulting locomotor performance will elucidate principles for effective motion on hysteretic materials. Future studies can leverage such knowledge of the benefits and limitations of different body–terrain interaction modes to tease apart neuromechanical control strategies for contending with natural terrains [29].…”

Section: Introductionmentioning

confidence: 99%

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Mitigating memory effects during undulatory locomotion on hysteretic materials

Schiebel

Astley

Rieser

et al. 2019

Preprint

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10Undulatory swimming in flowing media like water is well-studied, but little is known about loco-11 motion in environments that are permanently deformed by body-substrate interactions like snakes in 12 sand, eels in mud, and nematode worms in rotting fruit. We study the desert-specialist snake Chion-13 actis occipitalis traversing granular matter and find body inertia is negligible despite rapid transit 14 and speed dependent granular reaction forces. New surface resistive force theory (RFT) calculation 15 reveals how this snakes wave shape minimizes memory effects and optimizes escape performance 16 given physiological limitations (power). RFT explains the morphology and waveform dependent 17 performance of a diversity of non-sand-specialist, but overpredicts the capability of snakes with 18 high slip. Robophysical experiments recapitulate aspects of these failure-prone snakes and elucidate 19 how reencountering previously remodeled material hinders performance. This study reveals how 20 memory effects stymied the locomotion of a diversity of snakes in our previous studies [Marvi et 21 al, Science, 2014] and suggests the existence of a predictive model for history-dependent granular 22 physics. 23 I. INTRODUCTION 24Movement is critical to the survival of many organisms and a necessary ability in robots used in fields like medicine 25 [1], search and rescue [2], and extraterrestrial exploration [3]. This complex phenomenon emerges from the interplay 26 between a locomotor's internal body shape changes and the physics of the surroundings. Successful locomotion 27 thus depends on the execution of self-deformations which generate appropriate reaction forces from the terrain; a 28 relationship which can be further complicated if the body motion permanently changes the state of the substrate. 29 Much of our knowledge of terrestrial locomotion is in the regime of rigid materials where the terrain is not affected 30 by passage of the animal [4-7], leading to the development of robots which are effective on hard ground [8-10].31 Little is known about locomotion in non-rigid materials which are plastically deformed by the movement of animals 32 or robots, leaving tracks or footprints. Deformable terrains inhabit a spectrum from materials like water which 33 continuously flow toward the undisturbed, zero shear state [11] to those which are remodeled by the interaction, like 34 sand. Most work on motion in yielding materials has been on systems in which disturbances dissipate (fluids) [12-14]; 35 the impact of soft material hysteresis on locomotion is not well-understood [15]. 36 At one end of the spectrum, where deformations are short-lived [16], small fluid swimmers like the nematode 37 Caenorhabditis elegans [17], spermatazoa [18], and bacteria in water [19] and macroscale frictional-fluid swimmers like 38 the sandfish lizard and shovel-nosed snake moving subsurface through sand [5] use the resistance of the surrounding 39 material to the motion of their body shape changes to propel themselves. The fluid in these...

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Section: Discussionmentioning

confidence: 99%

Section: Performance Of Limbless Locomotors On Granular Materialsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mitigating memory effects during undulatory locomotion on hysteretic materials

Schiebel

Astley

Rieser

et al. 2019

Preprint

Self Cite

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“…See more detail of the interpolation method in (Mitchel et al 2020). We compared interpolation accuracy of our method to B-spline, a commonly used geometric interpolation method (Fontaine et al 2008;Padmanabhan et al 2012;Sharpe et al 2015;Socha et al 2018;Schiebel et al 2019), using the dataset of kingsnake traversing a large step We challenged the robot to traverse a high friction step obstacle with increasingly large step height, H = 31, 36, 38, and 40% of robot length L. Using the partitioned gait combining lateral oscillation with cantilevering from the snake, the robot rapidly traversed a step of height H = 31%…”

Section: Continuous Body 3-d Interpolationmentioning

confidence: 99%

Lateral Oscillation and Body Compliance Help Snakes and Snake Robots Stably Traverse Large, Smooth Obstacles

Fu¹,

Gart²,

Mitchel³

et al. 2020

Integrative and Comparative Biology

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SynopsisSnakes can move through almost any terrain. Similarly, snake robots hold the promise as a versatile platform to traverse complex environments like earthquake rubble. Unlike snake locomotion on flat surfaces which is inherently stable, when snakes traverse complex terrain by deforming their body out of plane, it becomes challenging to maintain stability. Here, we review our recent progress in understanding how snakes and snake robots traverse large, smooth obstacles like boulders and felled trees that lack "anchor points" for gripping or bracing. First, we discovered that the generalist variable kingsnake combines lateral oscillation and cantilevering. Regardless of step height and surface friction, the overall gait is preserved. Next, to quantify static stability of the snake, we developed a method to interpolate continuous body in three dimensions (both position and orientation) between discrete tracked markers. By analyzing the base of support using the interpolated continuous body 3-D kinematics, we discovered that the snake maintained perfect stability during traversal, even on the most challenging low friction, high step. Finally, we applied this gait to a snake robot and systematically tested its performance traversing large steps with variable heights to further understand stability principles. The robot rapidly and stably traversed steps nearly as high as a third of its body length. As step height increased, the robot rolled more frequently to the extent of flipping over, reducing traversal probability. The absence of such failure in the snake with a compliant body inspired us to add body compliance to the robot. With better surface contact, the compliant body robot suffered less roll instability and traversed high steps atIntegrative and Comparative Biology (2020), icaa013, https://doi.org/10.1093/icb/icaa013; https://li.me.jhu.edu/ 2 higher probability, without sacrificing traversal speed. Our robot traversed large step-like obstacles more rapidly than most previous snake robots, approaching that of the animal. The combination of lateral oscillation and body compliance to form a large, reliable base of support may be useful for snakes and snake robots to traverse diverse 3-D environments with large, smooth obstacles.

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“…A NIMALS often use limb and body contact to negotiate complex, cluttered environments. Snakes can use their body segments to push against grass stems to change their direction of movement [1], [2]. Cockroaches have been found to use different pitch and roll body angles to traverse dense, tall grass-like barriers of varying stiffness [3], [4].…”

Section: Introductionmentioning

confidence: 99%

Modulation of Robot Orientation Via Leg-Obstacle Contact Positions

Ramesh

Kathail

Koditschek

et al. 2020

IEEE Robot. Autom. Lett.

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We study a quadrupedal robot traversing a structured (i.e., periodically spaced) obstacle field driven by an open-loop quasi-static trotting walk. Despite complex, repeated collisions and slippage between robot legs and obstacles, the robot's horizontal plane body orientation (yaw) trajectory can converge in the absence of any body level feedback to stable steady state patterns. We classify these patterns into a series of "types" ranging from stable locked equilibria, to stable periodic oscillations, to unstable or mixed period oscillations. We observe that the stable equilibria can bifurcate to stable periodic oscillations and then to mixed period oscillations as the obstacle spacing is gradually increased. Using a 3Dreconstruction method, we experimentally characterize the robot leg-obstacle contact configurations at each step to show that the different steady patterns in robot orientation trajectories result from a selfstabilizing periodic pattern of leg-obstacle contact positions. We present a highly-simplified coupled oscillator model that predicts robot orientation pattern as a function of the leg-obstacle contact mechanism. We demonstrate that the model successfully captures the robot steady state for different obstacle spacing and robot initial conditions. We suggest in simulation that using the simplified coupled oscillator model we can create novel control strategies that allow multi-legged robots to exploit obstacle disturbances to negotiate randomly cluttered environments. For more information: Kod*lab (link to kodlab.seas.upenn.edu

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Mechanical diffraction reveals the role of passive dynamics in a slithering snake

Cited by 52 publications

References 39 publications

Mitigating memory effects during undulatory locomotion on hysteretic materials

Mitigating memory effects during undulatory locomotion on hysteretic materials

Lateral Oscillation and Body Compliance Help Snakes and Snake Robots Stably Traverse Large, Smooth Obstacles

Modulation of Robot Orientation Via Leg-Obstacle Contact Positions

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