Goldman, Daniel I.

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Comparative study of snake lateral undulation kinematics in model heterogeneous terrain dataset

2020-09-24 , Schiebel, Perrin E. , Hubbard, Alex M. , Goldman, Daniel I.

Terrestrial organisms that use traveling waves to locomote must leverage heterogeneities to overcome drag on the elongate body. While previous studies illuminated how habitat generalist snakes self-deform to use rigid obstacles in the surroundings, control strategies for multi-component terrain are largely unknown. We compared the sand-specialist Chionactis occipitalis to a habitat generalist, Pantherophis guttatus, navigating a model terrestrial terrain-rigid post arrays on a low-friction substrate. We found the waveshapes used by the generalist were more variable than the specialist. Principal component analysis revealed that while the specialized sand-swimming waveform was always present on C. occipitalis, the generalist did not have a similarly pervasive low-dimensional waveshape. We expected the generalist to thus outperform the specialist in the arrays, but body slip of both species was comparable on level ground and in all trials the snakes successfully traversed the arena. When we further challenged the snakes to ascend an inclined lattice, the sand-specialist had difficulty maintaining contact with the obstacles and was unable to progress up the steepest inclines in the largest lattice spacings. Our results suggest that species adapted to different habitats use different control modalities-the specialist is primarily controlling its kinematics to achieve a target shape while, consistent with previous research, the generalist is using force control and self-deforms in response to terrain contacts. While both strategies allowed progress on the uninclined low-friction terrain with posts, the more variable waveshapes of the generalist may be necessary when faced with more challenging locomotor tasks like climbing inclines.

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Tail use improves soft substrate performance in models of early vertebrate land locomotors

2016-05-27 , McInroe, Benjamin , Astley, Henry C. , Gong, Chaohui , Kawano, Sandy M. , Schiebel, Perrin E. , Rieser, Jennifer M. , Choset, Howie , Blob, Richard W. , Goldman, Daniel I.

In the evolutionary transition from an aquatic to a terrestrial environment, ancient vertebrates (e.g. early tetrapods) faced the challenges of terrestrial locomotion on flowable substrates (e.g. sand and mud) of variable stiffness and incline. While morphology and ranges of motion of appendages can be revealed in fossils, biological and robophysical studies of modern taxa demonstrate that movement on such substrates can be sensitive to small changes in appendage use. Using a biological model (the mudskipper), a physical model (a robot), granular drag measurements, and theoretical tools from geometric mechanics, we demonstrate how tail use can improve robustness to variable limb use and substrate conditions. We hypothesize that properly coordinated tail movements may have provided a substantial benefit for the earliest vertebrates to move on land.

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Tracked data for Chionactis occipitalis through a post array

2019-01-25 , Schiebel, Perrin E. , Rieser, Jennifer M. , Hubbard, Alex M. , Chen, Lillian , Rocklin, D. Zeb , Goldman, Daniel I.

Limbless animals like snakes inhabit most terrestrial environments, generating thrust to overcome drag on the elongate body via contacts with heterogeneities. The complex body postures of some snakes and the unknown physics of most terrestrial materials frustrates understanding of strategies for effective locomotion. As a result, little is known about how limbless animals contend with unplanned obstacle contacts. We studied a desert snake, Chionactis occipitalis, which uses a stereotyped head-to-tail traveling wave to move quickly on homogeneous sand. In laboratory experiments, we challenged snakes to move across a uniform substrate and through a regular array of force sensitive posts. The snakes were reoriented by the array in a manner reminiscent of the matter-wave diffraction of subatomic particles. Force patterns indicated the animals did not change their self-deformation pattern to either avoid or grab the posts. A model using open-loop control incorporating previously described snake muscle activation patterns and body-buckling dynamics reproduced the observed patterns, suggesting a similar control strategy may be used by the animals. Our results reveal how passive dynamics can benefit limbless locomotors by allowing robust transit in heterogeneous environments with minimal sensing.

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Mitigating memory effects during undulatory locomotion on hysteretic materials dataset

2019 , Schiebel, Perrin E. , Rieser, Jennifer M. , Astley, Henry C. , Agarwall, S. , Hubicki, C. , Hubbard, Alex M. , Cruz, K. , Mendelson, J. , Kamrin, K. , Goldman, Daniel I.

Undulatory swimming in flowing media like water is well studied, but little is known about locomotion in environments that are permanently deformed by body-substrate interactions like snakes in sand, eels in mud, and nematode worms in rotting fruit. We study the desert-specialist snake Chionactis occipitalis traversing granular matter and find body inertia is negligible despite rapid transit. New surface resistive force theory (RFT) calculation reveals this snake's waveform minimizes material memory effects and optimizes speed given anatomical limitations (power). RFT explains the morphology and waveform dependent performance of a diversity of non-sand-specialists, but over-predicts the capability of snakes with high slip. Robophysical experiments recapitulate aspects of these failure-prone snakes, elucidating how reencountering previously remodeled material hinders performance. This study reveals how memory effects stymied the locomotion of snakes in our previous study [Marvi et al, Science, 2014] and suggests the existence of a predictive model for history-dependent locomotion.