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Rapid inversion: running animals and robots swing like a pendulum under ledges.

Mongeau JM, McRae B, Jusufi A, Birkmeyer P, Hoover AM, Fearing R, Full RJ - PLoS ONE (2012)

Bottom Line: The smallest animals attain relatively fast speeds with high frequency leg cycling, wing flapping or body undulations, but absolute speeds are slow compared to larger animals.Instead, small animals benefit from the advantages of enhanced maneuverability in part due to scaling.Quantification of these acrobatic behaviors provides biological inspiration toward the design of small, highly mobile search-and-rescue robots that can assist us during natural and human-made disasters.

View Article: PubMed Central - PubMed

Affiliation: Biophysics Graduate Group, University of California, Berkeley, California, United States of America. jmmongeau@berkeley.edu

ABSTRACT
Escaping from predators often demands that animals rapidly negotiate complex environments. The smallest animals attain relatively fast speeds with high frequency leg cycling, wing flapping or body undulations, but absolute speeds are slow compared to larger animals. Instead, small animals benefit from the advantages of enhanced maneuverability in part due to scaling. Here, we report a novel behavior in small, legged runners that may facilitate their escape by disappearance from predators. We video recorded cockroaches and geckos rapidly running up an incline toward a ledge, digitized their motion and created a simple model to generalize the behavior. Both species ran rapidly at 12-15 body lengths-per-second toward the ledge without braking, dove off the ledge, attached their feet by claws like a grappling hook, and used a pendulum-like motion that can exceed one meter-per-second to swing around to an inverted position under the ledge, out of sight. We discovered geckos in Southeast Asia can execute this escape behavior in the field. Quantification of these acrobatic behaviors provides biological inspiration toward the design of small, highly mobile search-and-rescue robots that can assist us during natural and human-made disasters. We report the first steps toward this new capability in a small, hexapedal robot.

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Comparisons of animal and robot kinematics to a pendulum model.Panel (a) compares a pendulum model without transfer of kinetic energy (KE = 0; grey bob) and with complete transfer of kinetic energy (KE>0; magenta bob) to the animal and robot trajectories as a function of time (ms) from representative position data from the COM of the cockroach (red), gecko (green), and robot (blue). The pendulum base joint represents the average position of the feet during the maneuver. The cockroach and gecko started swinging at an angle of approximately 30 degrees from the body long axis relative to the horizontal, whereas the robot initiated swinging near the horizontal relative to the body long axis (0 degree). Panel (b) shows the change in angle relative to the initial angle at the start of the swing for animals and robot compared to our two models. Panel (c) shows the speed of the animals and robot. The grey area represents the period of swinging defined as the point of slowest speed following foot engagement until all legs contacted the underside of the ledge. Panel (d) shows the position of the COM of the animals and robot during the complete rapid inversion maneuver for a representative trial. Arrows indicate the resultant velocity vectors (m s–1) at intervals of 20 ms. The black open circle indicates the region where the speed is slowest. Panel (e) shows the corresponding energy profiles. The grey area represents the same period as defined in (c) above. The dashed curve in magenta shows the total kinetic energy for the pendulum model if transfer were complete.
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pone-0038003-g004: Comparisons of animal and robot kinematics to a pendulum model.Panel (a) compares a pendulum model without transfer of kinetic energy (KE = 0; grey bob) and with complete transfer of kinetic energy (KE>0; magenta bob) to the animal and robot trajectories as a function of time (ms) from representative position data from the COM of the cockroach (red), gecko (green), and robot (blue). The pendulum base joint represents the average position of the feet during the maneuver. The cockroach and gecko started swinging at an angle of approximately 30 degrees from the body long axis relative to the horizontal, whereas the robot initiated swinging near the horizontal relative to the body long axis (0 degree). Panel (b) shows the change in angle relative to the initial angle at the start of the swing for animals and robot compared to our two models. Panel (c) shows the speed of the animals and robot. The grey area represents the period of swinging defined as the point of slowest speed following foot engagement until all legs contacted the underside of the ledge. Panel (d) shows the position of the COM of the animals and robot during the complete rapid inversion maneuver for a representative trial. Arrows indicate the resultant velocity vectors (m s–1) at intervals of 20 ms. The black open circle indicates the region where the speed is slowest. Panel (e) shows the corresponding energy profiles. The grey area represents the same period as defined in (c) above. The dashed curve in magenta shows the total kinetic energy for the pendulum model if transfer were complete.

Mentions: We tested the hypothesis that animals swung around to the underside of the ledge like a pendulum by first comparing the swing kinematics to a physical pendulum model with zero transfer of kinetic energy as a hypothesis. We determined the parameters of the pendulum model using estimates of morphology and matching the initial conditions to the animal or robot positions (see Methods). If we assume that the body or center of mass of the animal or robot represents the bob of a pendulum subject to only gravitational force and starting from rest with no added kinetic energy, then we can trace the trajectory from the time the animal engages its claw or the robot sticks until the swing underneath the ledge is complete (Fig. 4a; grey circles).


Rapid inversion: running animals and robots swing like a pendulum under ledges.

Mongeau JM, McRae B, Jusufi A, Birkmeyer P, Hoover AM, Fearing R, Full RJ - PLoS ONE (2012)

Comparisons of animal and robot kinematics to a pendulum model.Panel (a) compares a pendulum model without transfer of kinetic energy (KE = 0; grey bob) and with complete transfer of kinetic energy (KE>0; magenta bob) to the animal and robot trajectories as a function of time (ms) from representative position data from the COM of the cockroach (red), gecko (green), and robot (blue). The pendulum base joint represents the average position of the feet during the maneuver. The cockroach and gecko started swinging at an angle of approximately 30 degrees from the body long axis relative to the horizontal, whereas the robot initiated swinging near the horizontal relative to the body long axis (0 degree). Panel (b) shows the change in angle relative to the initial angle at the start of the swing for animals and robot compared to our two models. Panel (c) shows the speed of the animals and robot. The grey area represents the period of swinging defined as the point of slowest speed following foot engagement until all legs contacted the underside of the ledge. Panel (d) shows the position of the COM of the animals and robot during the complete rapid inversion maneuver for a representative trial. Arrows indicate the resultant velocity vectors (m s–1) at intervals of 20 ms. The black open circle indicates the region where the speed is slowest. Panel (e) shows the corresponding energy profiles. The grey area represents the same period as defined in (c) above. The dashed curve in magenta shows the total kinetic energy for the pendulum model if transfer were complete.
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Related In: Results  -  Collection

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pone-0038003-g004: Comparisons of animal and robot kinematics to a pendulum model.Panel (a) compares a pendulum model without transfer of kinetic energy (KE = 0; grey bob) and with complete transfer of kinetic energy (KE>0; magenta bob) to the animal and robot trajectories as a function of time (ms) from representative position data from the COM of the cockroach (red), gecko (green), and robot (blue). The pendulum base joint represents the average position of the feet during the maneuver. The cockroach and gecko started swinging at an angle of approximately 30 degrees from the body long axis relative to the horizontal, whereas the robot initiated swinging near the horizontal relative to the body long axis (0 degree). Panel (b) shows the change in angle relative to the initial angle at the start of the swing for animals and robot compared to our two models. Panel (c) shows the speed of the animals and robot. The grey area represents the period of swinging defined as the point of slowest speed following foot engagement until all legs contacted the underside of the ledge. Panel (d) shows the position of the COM of the animals and robot during the complete rapid inversion maneuver for a representative trial. Arrows indicate the resultant velocity vectors (m s–1) at intervals of 20 ms. The black open circle indicates the region where the speed is slowest. Panel (e) shows the corresponding energy profiles. The grey area represents the same period as defined in (c) above. The dashed curve in magenta shows the total kinetic energy for the pendulum model if transfer were complete.
Mentions: We tested the hypothesis that animals swung around to the underside of the ledge like a pendulum by first comparing the swing kinematics to a physical pendulum model with zero transfer of kinetic energy as a hypothesis. We determined the parameters of the pendulum model using estimates of morphology and matching the initial conditions to the animal or robot positions (see Methods). If we assume that the body or center of mass of the animal or robot represents the bob of a pendulum subject to only gravitational force and starting from rest with no added kinetic energy, then we can trace the trajectory from the time the animal engages its claw or the robot sticks until the swing underneath the ledge is complete (Fig. 4a; grey circles).

Bottom Line: The smallest animals attain relatively fast speeds with high frequency leg cycling, wing flapping or body undulations, but absolute speeds are slow compared to larger animals.Instead, small animals benefit from the advantages of enhanced maneuverability in part due to scaling.Quantification of these acrobatic behaviors provides biological inspiration toward the design of small, highly mobile search-and-rescue robots that can assist us during natural and human-made disasters.

View Article: PubMed Central - PubMed

Affiliation: Biophysics Graduate Group, University of California, Berkeley, California, United States of America. jmmongeau@berkeley.edu

ABSTRACT
Escaping from predators often demands that animals rapidly negotiate complex environments. The smallest animals attain relatively fast speeds with high frequency leg cycling, wing flapping or body undulations, but absolute speeds are slow compared to larger animals. Instead, small animals benefit from the advantages of enhanced maneuverability in part due to scaling. Here, we report a novel behavior in small, legged runners that may facilitate their escape by disappearance from predators. We video recorded cockroaches and geckos rapidly running up an incline toward a ledge, digitized their motion and created a simple model to generalize the behavior. Both species ran rapidly at 12-15 body lengths-per-second toward the ledge without braking, dove off the ledge, attached their feet by claws like a grappling hook, and used a pendulum-like motion that can exceed one meter-per-second to swing around to an inverted position under the ledge, out of sight. We discovered geckos in Southeast Asia can execute this escape behavior in the field. Quantification of these acrobatic behaviors provides biological inspiration toward the design of small, highly mobile search-and-rescue robots that can assist us during natural and human-made disasters. We report the first steps toward this new capability in a small, hexapedal robot.

Show MeSH
Related in: MedlinePlus