Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y12: Robophysics IIFocus
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Sponsoring Units: GSNP DBIO GSOFT Chair: Daniel Goldman, GeorgiaTech Room: 271 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y12.00001: Induced vibrations increase performance of a winged self-righting robot Ratan Othayoth, Qihan Xuan, Chen Li When upside down, cockroaches can open their wings to dynamically self-right. In this process, an animal often has to perform multiple unsuccessful maneuvers to eventually right, and often flails its legs. Here, we developed a cockroach-inspired winged self-righting robot capable of controlled body vibrations to test the hypothesis that vibrations assist self-righting transitions. Robot body vibrations were induced by an oscillating mass (10{\%} of body mass) and varied by changing oscillation frequency. We discovered that, as the robot's body vibrations increased, righting probability increased, and righting time decreased (P \textless 0.0001, ANOVA), confirming our hypothesis. To begin to understand the underlying physics, we developed a locomotion energy landscape model. Our model revealed that the kinetic energy fluctuations due to vibrations were comparable to the potential energy barriers required to transition from a metastable overturned orientation to an upright orientation. Our study supports the plausibility of locomotion energy landscapes for understanding locomotor transitions, but highlights the need for further stochastic modeling to capture the uncertain nature of when righting maneuvers result in successful righting. \newline [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y12.00002: Body shape helps legged robots climb and turn in complex 3-D terrains Yuanfeng Han, Zheliang Wang, Chen Li Analogous to streamlined shapes that reduce drag in fluids, insects' ellipsoid-like rounded body shapes were recently discovered to be ``terradynamically streamlined'' and enhance locomotion in cluttered terrain by facilitating body rolling. Here, we hypothesize that there exist more terradynamic shapes that facilitate other modes of locomotion like climbing and turning in complex 3-D terrains by facilitating body pitching and yawing. To test our hypothesis, we modified the body shape of a legged robot by adding an elliptical and a rectangular shell and tested how it negotiated with circular and square vertical pillars. With a rectangular shell the robot always pitched against square pillars in an attempt to climb, whereas with an elliptical shell it always yawed and turned away from circular pillars given a small initial lateral displacement. Square / circular pillars facilitated pitching / yawing, respectively. To begin to reveal the contact physics, we developed a locomotion energy landscape model. Our model revealed that potential energy barriers to transition from pitching to yawing are high for angular locomotor and obstacle shapes (rectangular / square) but vanish for rounded shapes (elliptical / circular). Our study supports the plausibility of locomotion energy landscapes for understanding the rich locomotor transitions in complex 3-D terrains. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y12.00003: Paused intrusions improve robot jumping performance in granular media Christian Hubicki, Jeffrey Aguilar, Allison Kim, Jennifer Rieser, Aaron Ames, Daniel Goldman Modeling locomotion of robots requires understanding the physics of interaction with the environment. Previously [Aguilar {\&} Goldman, Nat. Phys., 2015] we studied vertical jumping on granular media with a robot consisting of a position controlled mass in series with a spring connected to a circular foot; a granular resistive force theory model containing a depth dependent force modified to account for added mass captured performance over a wide range of parameters. We have now discovered that while continuous intrusion into loosely packed granular media results in forces which increase monotonically with depth, brief (\textasciitilde 500 ms) pauses during intrusion result in force overshoots (10-35{\%}) relative to the force at that depth during continuous intrusion. Laser speckle measurements of the grains beneath the intruder reveal a settling of sub-grain-scale motion over 10-1000 ms time scales; we hypothesize that this results in jammed states beneath the foot. To test if this effect can be exploited to improve jump performance, we program the robot using continuous and paused thrust (20-30 ms) behaviors. While both jumps yield identical jump heights in a bulk reaction force model, the paused maneuvers jump 10-40{\%} higher than their counterparts. [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y12.00004: Overshoot intrusion forces promote robophysical bipedal walking on homogenous granular media Xiaobin Xiong, Jeffrey Aguilar, Jennifer Rieser, Allison Kim, Aaron Ames, Daniel Goldman Bipedal walking on natural terrain such as sand and loose rubble is challenging because deformable terrains complicate foot-terrain interaction (modelled as rigid contact on hard ground). To discover how deformable ground interaction influences bipedal walking, we study constant center-of-mass height dynamic walking of a flat-footed bipedal robophysical device (40cm tall, 3 motors per leg) on homogeneous granular terrain of loosely packed poppy seeds. The planarized robot is controlled such that its zero-moment point (ZMP) stays within a stability region (termed support polygon for hard ground walking). Granular resistive force theory [Li et al, Science 2013] fails to predict this stability region despite success in predicting performance of multi-legged robots on granular media. We posit that the stability region formulation requires understanding of static reaction forces; we estimate these effects by measuring forces on a flat plate (3cmx3cm) vertically plunged (at $\approx 1$ cm/second) into loosely packed poppy seeds with controlled pauses during the intrusion. Following a pause ($\approx 3$ second), the force overshoots 13\%-38\% to that of continuous intrusion at depths from 45mm-5mm. The overshoot forces rationalize the stability regions and enable robust bipedal walking. [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y12.00005: Mitigating clogging and arrest in confined self-propelled systems William Savoie, Jeffrey Aguilar, Daria Monaenkova, Vadim Linevich, Daniel Goldman Ensembles of self-propelling elements, like colloidal surfers, bacterial biofilms, and robot swarms can spontaneously form density heterogeneities. To understand how to prevent potentially catastrophic clogs in task-oriented active matter systems (like soil excavating robots), we present a robophysical study of excavation of granular media in a confined environment. We probe the efficacy of two social strategies observed in our studies of fire ants (S. invicta). The first behavior (denoted as “unequal workload”) prescribes to each excavator a different probability to enter the digging area. The second behavior (denoted as “reversal”), is characterized by a probability to forfeit excavation when progress is sufficiently obstructed. For equal workload distribution and no reversal behavior, clogs at the digging site prevent excavation for sufficient numbers of robots. Measurements of aggregation relaxation times reveal how the strategies mitigate clogs. The unequal workload behavior reduces the tunnel density, decreasing the probability of clog formation. Reversal behavior, while allowing clogs to form, reduces aggregation relaxation time. We posit that application of social behaviors can be useful for swarm robot systems where global control and organization may not be possible. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y12.00006: Coordinated Body Bending Improves Performance of a Salamander-like Robot yasemin ozkan aydin, Baxi Chong, Chaohui Gong, Jennifer M. Rieser, Howie Choset, Daniel I. Goldman Analyzing body morphology and limb-body coordination in animals that can both swim and walk is important to understand the evolutionary transition from an aquatic to a terrestrial environment. Based on previous salamander experiments (a modern analog to early tetrapods and performed by Hutchinson's group at RVC in the UK) we built a robophysical model of a salamander and tested its performance on yielding granular media (GM) of poppy seeds. Our servo-driven robot (405 g, 38 cm long) has four limbs, a flexible body, and an active tail. Each limb has two servo motors to control up/down and fore/aft positions of limb. A joint in the middle of the body controls horizontal bending. We assessed performance of the robot by changing the body bending limit from $0^{\circ}$to $90^{\circ}$and measured body displacement and power consumption over a few limb cycles at $0^{\circ}$and $10^{\circ}$sandy slope. We fixed the angle of the legs according to body to test the effect of body bending directly. On GM, step length increased from 0 to 9.5 cm at $0^{\circ}$ and 0 to 7 cm at $10^{\circ}$slope while the average power consumption increased $50\% $. A geometric mechanics model revealed that on level GM body bending was most beneficial when phase offset $180^{\circ}$from leg movements; increasing the maximum body angular bend from $45^{\circ}$to $90^{\circ}$ led to step length increases of up to $90\% $. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y12.00007: Deformation-Induced Precession of a Robot Moving on Curved Space Shengkai Li, Yasemin Aydin, Olivia Lofaro, Jennifer Rieser, Daniel Goldman Previous studies have demonstrated that passive particles rolling on a deformed surface can mimic aspects of general relativity [Ford et al, AJP, 2015]. However, these systems are dissipative. To explore steady-state dynamics, we study the movement of a self-propelled robot car on a large deformable elastic membrane: a spandex sheet stretched over a metal frame with a diameter of 2.5 m. Two wheels in the rear of the car are differentially-driven by a DC motor, and a caster in the front helps maintain directional stability; in the absence of curvature the car drives straight. A linear actuator attached below the membrane allows for controlled deformation at the center of the membrane. We find that closed elliptic orbits occur when the membrane is highly depressed ($\sim $10 cm). However, when the center is only slightly indented, the elliptical orbits precess at a rate depending on the orbit shape and the depression. Remarkably, this dynamic is well described by the Schwarzschild metric solution, typically used to describe the effects of gravity on bodies orbiting a massive object. Experiments with multiple cars reveal complex interactions that are mediated through car-induced deformations of the membrane. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y12.00008: Mechanical diffraction of a snake-like robot through an array of pegs Jennifer Rieser, Perrin Schiebel, Arman Pazouki, Alex Hubbard, Feifei Qian, Zachary Goddard, Tingnan Zhang, Andrew Zangwill, Dan Negrut, Daniel Goldman Snakes successfully navigate through a diversity of environments which can include hard ground, loose sand, twigs and leaf litter. Despite the seeming simplicity of this movement, the interaction with the ground coupled with intermittent obstacle collisions can give rise to complex dynamics. We study these interactions in a model system, in which a 13-segment snake-like robot interacts with a row of five evenly-spaced vertical pegs oriented perpendicular to the robot\textsc{\char13}s initial direction of motion. The robot is placed at different positions within a region with lateral and longitudinal dimensions set by the peg spacing and distance traveled in one undulation cycle. Forces imparted to the pegs are recorded as a function of time, revealing that the robot preferentially applies forces to the sides of the pegs and that contributions from all segments are significant. Despite the complexity of these interactions, we find that the robot emerges along preferred paths, which we characterize by the angle of rotation of the direction of travel, and that these angles decrease with increasing peg spacing. Numerical simulations are in excellent agreement with experiments and allow for a more thorough exploration of this dependence. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y12.00009: Induced vibrations facilitate traversal of cluttered obstacles George Thoms, Siyuan Yu, Yucheng Kang, Chen Li When negotiating cluttered terrains such as grass-like beams, cockroaches and legged robots with rounded body shapes most often rolled their bodies to traverse narrow gaps between beams. Recent locomotion energy landscape modeling suggests that this locomotor pathway overcomes the lowest potential energy barriers. Here, we tested the hypothesis that body vibrations induced by intermittent leg-ground contact facilitate obstacle traversal by allowing exploration of locomotion energy landscape to find this lowest barrier pathway. To mimic a cockroach / legged robot pushing against two adjacent blades of grass, we developed an automated robotic system to move an ellipsoidal body into two adjacent beams, and varied body vibrations by controlling an oscillation actuator. A novel gyroscope mechanism allowed the body to freely rotate in response to interaction with the beams, and an IMU and cameras recorded the motion of the body and beams. We discovered that body vibrations facilitated body rolling, significantly increasing traversal probability and reducing traversal time (P \textless 0.0001, ANOVA). Traversal probability increased with and traversal time decreased with beam separation. These results confirmed our hypothesis and support the plausibility of locomotion energy landscapes for understanding the formation of locomotor pathways in complex 3-D terrains. \newline [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y12.00010: Digging the termite way: crowding simple robots to excavate ramification structures. Paul Bardunias The complex ramification network that termites excavate in soil in search of resources has been shown to emerge from interactions between individuals during periodic crowding at the tips of tunnels. Excavation in these social insects is carried out by a rotation of termites removing soil from the tip of an expanding tunnel and depositing it back along the tunnel walls. Bristle bots, modified to either rock or turn on contact with soil in an artificial tunnel, were used to replicate this process. As in termites, congestion at tunnel tips leads to the widening and branching of tunnels. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y12.00011: Soft Snakes: Construction, Locomotion, and Control Callie Branyan, Taylor Courier, Chloe Fleming, Jacquelin Remaley, Ross Hatton, Yigit Menguc We fabricated modular bidirectional silicone pneumatic actuators to build a soft snake robot, applying geometric models of serpenoid swimmers to identify theoretically optimal gaits to realize serpentine locomotion. With the introduction of magnetic connections and elliptical cross-sections in fiber-reinforced modules, we can vary the number of continuum segments in the snake body to achieve more supple serpentine motion in a granular media. The performance of these gaits is observed using a motion capture system and efficiency is assessed in terms of pressure input and net displacement. These gaits are optimized using our geometric “soap-bubble method” of gait optimization, demonstrating the applicability of this tool to soft robot control and coordination. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y12.00012: How seabirds plunge-dive without injuries Brian Chang, Matthew Croson, Lorian Straker, Sean Gart, Carla Dove, John Gerwin, Sunghwan Jung In nature, several seabirds (e.g., gannets and boobies) dive into water at up to 24 m/s as a hunting mechanism; furthermore, gannets and boobies have a slender neck, which is potentially the weakest part of the body under compression during high-speed impact. In this work, we investigate the stability of the bird’s neck during plunge-diving by understanding the interaction between the fluid forces acting on the head and the flexibility of the neck. First, we use a salvaged bird to identify plunge-diving phases. Anatomical features of the skull and neck were acquired to quantify the effect of beak geometry and neck musculature on the stability during a plunge-dive. Second, physical experiments using an elastic beam as a model for the neck attached to a skull-like cone revealed the limits for the stability of the neck during the bird’s dive as a function of impact velocity and geometric factors. We find that the neck length, neck muscles, and diving speed of the bird predominantly reduce the likelihood of injury during the plunge-dive. Finally, we use our results to discuss maximum diving speeds for humans to avoid injury. [Preview Abstract] |
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