Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q03: Robophysics IIFocus Recordings Available
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Sponsoring Units: DBIO GSNP Chair: Feifei Qian, University of Southern California Room: McCormick Place W-176A |
Wednesday, March 16, 2022 3:00PM - 3:36PM |
Q03.00001: Principled understanding of dynamic multi-legged locomotion in complex terrain Invited Speaker: Chen Li Research on dynamic multi-legged locomotion on relatively flat, rigid surfaces significantly advanced our understanding of how animals walk and run and provided foundations for multi-legged robots that do so dynamically, stably, and efficiently. Here I review recent research building on these early insights to further understand dynamic multi-legged locomotion in complex terrain such as granular media like dry sand and cluttered large obstacles. An interdisciplinary approach at the interface of biology, engineering, and physics integrating rigorous, systematic experiments and first-principle modeling proved powerful in revealing novel insights and surprisingly general principles. Analogous to aero- and hydrodynamics that describe fluid-structure interaction and have advanced understanding of flight and swimming, these efforts are establishing a new field of terradynamics of locomotor-terrain interaction and have advanced understanding of animal and robot locomotion in complex terrain. Many questions still remain, calling for continued creation of new experimental tools and theoretical and computational models to address challenges of increasing complexity in measuring locomotion and defining environmental physics, as well as broad interdisciplinary training and collaboration. |
Wednesday, March 16, 2022 3:36PM - 3:48PM |
Q03.00002: A mode map model to predict state transitions of multi-legged robots within obstacle fields Haodi Hu, Matthew D Kvalheim, Feifei Qian Environments filled with large obstacles such as rocks and boulders are challenging for legged robots. Inspired by the agile movements achievable by humans and animals through actively engaging obstacles, we (i) investigate how robot gaits affect robot dynamics during repeated contact with obstacles, and (ii) seek locomotion strategies that exploit the "disturbances" caused by robot-obstacle contacts to produce desired trajectories. |
Wednesday, March 16, 2022 3:48PM - 4:00PM |
Q03.00003: Locomotion in Granular Media: A Geomechanical Perspective on Symmetry Breaking Sichuan Huang, Junliang Tao Biological organisms exploit cyclic body shape changes to locomote underground. These body shape changes are either symmetrical or asymmetrical in time. Examples include the cyclic extension/contraction adopted by the Atlantic razor clam to burrow upward from sands, and the helical drilling used by scarab beetle larva and some seed awns for submerging in soil. Overall, locomotion requires organisms to overcome resistances to advance forward and form anchorage to prevent slip backward. This study investigates the correlation between underground locomotion and the symmetricity of cyclic body shape changes from a geomechanics perspective. We design a modular robot that features an extensible cylindrical body and a rotatable helictical tip. The robot can move in granular media horizontally and automatically through cyclic extension and contraction, facilitated by tip rotation. Nonetheless, negligible movement occurs as the robot extends and contracts without the tip. We then evaluate the robot's burrowing performance, and monitor the particle displacement fields around the robot to facilitate understanding of the underlying burrowing mechanism. Insights into the general principle of locomotion in granular media are discussed by comparing to swimming in low Reynolds number fluids. |
Wednesday, March 16, 2022 4:00PM - 4:12PM |
Q03.00004: Reducing model fidelity for statistical path characterization of an insect-scale robot Henry Cerbone, Perrin E Schiebel, Robert J Wood Studies of both insect and robot locomotion have shown the usefulness of open-loop control for traversing heterogeneous terrain. An unanswered question is how to incorporate the effectiveness of open-loop control on feature-laden terrain with path planning techniques. We previously studied open-loop running across 3D printed models of feature-laden terrains with the 1.4~g quadrupedal Harvard Ambulatory Microrobot. We tested running frequencies both at and above the robot's center-of-mass resonances. When running near resonance, random perturbations from limb-ground interactions resulted in a mean-square displacement characteristic of diffusion at time scales of a few steps, resulting in trajectories with stochastic properties. In this work, we explore a modelling technique for an insect scale, robotic locomotor that abstracts the complex leg and foot-ground interactions by leveraging past experimental data. The model developed treats the problem of trajectory planning as a statistical one, abstracting away complex dynamics models which become increasingly inaccurate as terrain complexity leads to harder to predict foot-ground interactions. This reduction of model fidelity leads to a statistical characterization of the robot's trajectory for use in terrain exploration and mapping. |
Wednesday, March 16, 2022 4:12PM - 4:24PM |
Q03.00005: A multi-legged robot traverses heterogeneous 3-D terrain via locomotor transitions Jonathan Mi, Yaqing Wang, Qihan Xuan, Chen Li Robots still struggle to traverse heterogeneous 3-D terrain cluttered with a variety of large obstacles. In contrast, small animals like cockroaches excel at doing so by using and controlling physical interaction with the terrain. Our recent research studied distinct locomotor challenges abstracted from such terrain—traversing large bumps, gaps, pillars, and flexible beams, and self-righting—and discovered strategies to overcome them (Othayoth et al. 2020, Proc. Roy. Soc. B). Here, we developed a multi-legged robot to integrate these strategies. A streamlined body shape enabled pillar traversal by passive obstacle repulsion and helped beam traversal by enhancing body rolling into gaps. Two active wings enabled self-righting by lifting the center of mass and reducing roll stability. An active tail facilitated bump traversal by pitching the body up using inertial effect, aided beam traversal by pushing against the ground to roll the body, and assisted self-righting by lateral perturbation. The robot traversed a bump of 2.5× hip height, pillars spaced 1.1× body width, and beams spaced 0.7× body width and self-righted within 4 s. We also developed a multi-body dynamics simulation of the physical robot and will use them to study sensory feedback principles for autonomous transitions. |
Wednesday, March 16, 2022 4:24PM - 4:36PM |
Q03.00006: Planning of Obstacle-aided Navigation for Multi-legged Robots using a Sampling-based Method over Directed Graphs Kaustav Chakraborty, Matthew D Kvalheim, Feifei Qian Most of the existing work in mobile robot navigation approaches the problem with the assumption of flat, rigid ground and requires avoidance of all robot-obstacle contacts. Here we develop a method that allows multi-legged robots to achieve desired dynamics by taking advantage of their interactions with obstacles. Our method utilizes a discrete-time reduced-order robophysics model which faithfully captures the obstacle-modulated, horizontal-plane robot dynamics. We discretize this reduced-order model by constructing a directed graph that can be used to approximate the long-term behaviors of our system. The directed graph allows for systematic analysis of steady-state behaviors and begins to provide guarantees on stability and robustness. Searching over the graph using sampling-based planners can provide feasible paths in the robot's gait space to achieve desired locomotion and navigation goals by exploiting robot-obstacle interactions. A standout feature of a path so found by our planning algorithm is the explicit use of obstacles to aid in the navigation. We demonstrate the capabilities of our method in finding obstacle-aided navigational strategies through simulation as well as physical experiments on a quadrupedal robot traversing over a periodic obstacle field. |
Wednesday, March 16, 2022 4:36PM - 4:48PM |
Q03.00007: A novel insect scale autonomous soft quadrupedal robot for locomotion through 3D complex terrain Heiko D Kabutz, Kaushik Jayaram Animals such as mice, cockroaches and spiders have the remarkable ability to manoeuvre through challenging cluttered natural terrain. These abilities have been inspiration for legged robotic systems. Recent research indicates that body reorientation along pathways of minimal energy is a key factor influencing such locomotion. We propose to extend this idea with hypothesizing body compliance of soft bodied animals and robots as an alternate yet equally effective strategy to squeeze through cluttered obstacles. We have developed an insect-scale, origami-based quadrupedal robot, CLARI. The robot has body compliance through exoskeletal morphology. Using a carbon fibre multilayer laminate laser micromachining technique and piezoelectric actuators, four independently two degree of freedom legs are controlled. Additional electro adhesive feet allow for controlled motion across non-level surfaces. With the compliance of the exoskeleton CLARI can passively conform to its environment. We aim to verify our hypothesis by constructing a series of insect scale robots with varying body compliance and experimentally determining the preference for body deformation vs reorientation in a given cluttered environment for identical feedforward control commands. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q03.00008: Low Slip Bipedal Locomotion on Granular Slopes via Cleated Foot Interaction Deniz Kerimoglu, Daniel I Goldman Bipedal locomotion on steep granular slopes can be challenging due to slipping and tilting, typically resulting from media yielding and downhill flow [Marvi et al, Science, 2014]. To gain insight into the relevant granular physics and develop robots that can traverse sandy slopes, we performed systematic experiments on a planar biped robot that self-deforms via hip, knee, and ankle actuation. Due to limited understanding of feedback control mechanisms on flowable terrain, we first develop open-loop gait trajectories to generate stable locomotion: trajectories on flat media are hand-tuned to slopes (consisting of loosely packed poppy seeds) by shifting the robot's center of mass accordingly, preventing the robot from tilting. We achieve stable locomotion on uphill/downhill granular slopes of ±10 degrees, slipping at each step at most 10% of its step length. To extend locomotion capability to steeper slopes, we replace the flat feet with cleated feet consisting of thin blades emanating vertically from the foot. The blades insert fully into the medium with low intrusion force, allowing the material to remain near or below yield stress. Cleated feet allow robot locomotion with moderate slip (%50) on granular slopes close to the angle of maximum slope stability (± 27 deg). |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q03.00009: Robophysical and simulation modeling of how leg posture affects vibration sensing in orb weaving spiders Eugene Lin, Yishun Zhou, Andrew Gordus, Chen Li Orb-weaving spiders, which make 2-D webs, are functionally blind and use legs to sense web vibrations to identify and locate prey on the web. When doing so, they often adjust their leg posture. Recent simulation of black widows, which make 3-D cob webs (Mhatre et al. 2018 biorxiv), suggested that spiders may adjust leg posture to "tune in" to certain vibration frequencies to enhance target identification (whether it is prey, a mate, or another object). Here we developed a robophysical model spider to test whether this is true in a real system. Each leg consisted of two joints with torsion springs and variable equilibrium angles to adjust leg posture and accelerometers to measure leg vibration. We also developed a multi-body dynamics simulation robot, which can be used for easier systematic parameter variation and more comprehensive measurements of vibration dynamics. As a first step, we applied an impact on one leg in both the physical and simulation robots while fixing the other legs. Changing leg posture indeed significantly altered the sensed vibration, confirming the hypothesis. We are validating simulation against experiment and adding a 2-D web in both experiment and simulation to understand the principles of vibration sensing modulation by leg posture on the web. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q03.00010: Robophysics-inspired biology experiments to study gait control for obstacle negotiation in canines Michelle Joyce, Simon Wilshin, Andrew Spence Determining strategies for stable and economical locomotion in robots in complex environments can be inspired by biology, and in turn, results from robotic locomotion can inspire a unique approach to studying the biomechanics of how animals overcome obstacles. We explore how gait types and environment structure influence the way quadrupedal animals, here dogs, negotiate obstacles. Prior research shows trajectories of stable locomotion emerge based on direct leg-obstacle interactions in a quadrupedal robot as it moves over a regular array of domed obstacles. Considering a dog's flexibility and tradeoffs between desired gait, navigation, and energy expenditure, we hypothesized that in a similar array, dogs would change gait parameters including duty factor, limb phase, stride length, as well as direction of locomotion. These factors are compared in 11 dogs, by adjusting the spacing between the obstacles to 20% greater than and less than each dog's natural trotting step length. Results indicate that dogs will focus on obstacle avoidance by changing gait parameters with both minor continuous adjustments (values of duty factor), and large infrequent adjustments (jumping over obstacles), in response to variation in the spacing size between obstacles. |
Wednesday, March 16, 2022 5:24PM - 5:36PM |
Q03.00011: SLIP-Inspired Hopping on Yielding Terrain Daniel J Lynch, Kevin M Lynch, Paul B Umbanhowar Legged robots offer the possibility of superior performance relative to wheeled or treaded vehicles on yielding substrates. However, the tools for planning and controlling legged locomotion on these substrates are significantly less advanced than their rigid-ground counterparts, due largely to nontrivial coupling between ground reaction forces and foot kinematics and irrecoverable energy loss through permanent terrain deformation. We recently addressed these challenges using direct-collocation trajectory optimization, informed by resistive force theory (RFT), discovering hopping gaits for a monopod that closely resemble the spring-loaded inverted pendulum (SLIP) motions characteristic of running animals. Inspired by these results, and within the same RFT framework, we develop and implement an augmented SLIP template parameterized by leg and ankle impedance. We optimize these parameters to maximize energetic efficiency, forward speed, and robustness during steady-state hopping on yielding terrain. These results lay the groundwork for a two-pronged approach that will use control and foot design to explore the tradeoffs between efficient, agile, and robust legged locomotion on soft ground. |
Wednesday, March 16, 2022 5:36PM - 5:48PM |
Q03.00012: Passive mechanical limb features facilitate rough terrain locomotion of an insect-scale robot. Perrin E Schiebel, Pierre-Louis Lechere, Robert J Wood Insects and robots traversing rugged terrain are aided by mechanical features in the limbs that passively contend with unexpected interactions. Strategies for navigating complex terrain with minimal sensing and computation are needed for small robots, such as the 1.4 g quadrupedal Harvard ambulatory microrobot we previously studied running in open-loop on 3D printed models of complex terrains. We observed two primary sources of performance degradation: colliding with features during the swing phase, which could halt or even reverse forward motion, and jamming of the limb tip in local minima. Including a linear elastic knee joint with a kneecap which allowed only posterior bending allowed the robot to bypass a wall obstacle while still moving effectively on a featureless surface. Performance was sensitive to the elasticity of the hinge, controlled via hinge width. Adding teeth to the front surface of the leg, inspired by the hairs on insect limbs, was necessary for success by allowing the bent limb to provide propulsive forces when in contact with the obstacle. An ant-inspired foot that increased surface area helped prevent the limb tip from getting stuck in small gaps in the terrain. This provides further evidence of the utility of multiscale, multi-modal limb features. |
Wednesday, March 16, 2022 5:48PM - 6:00PM |
Q03.00013: Force sensing facilitates traversal in cluttered beams with interaction Qihan Xuan, Yaqing Wang, Chen Li Robots often struggle in traversing cluttered obstacles, while animals are good at it. For example, the discoid cockroach can traverse cluttered grass-like beams with physical interaction in various ways (Othayoth, Thoms, Li, 2020, PNAS). The animal pushes across flimsy beams, but it usually rolls its body to traverse stiff beams, which overcomes a lower potential energy barrier. To make this transition, besides using kinetic energy fluctuation from self-propulsion, the animal also adjusts its head, abdomen, and legs (Wang, Othayoth, Li, 2021, J. Exp. Biol., in review). This suggests that the animal can sense resistive forces and actively switch to the less costly roll mode. To test this hypothesis, we developed a physics model of a robot capable of environmental force sensing propelled forward to traverse beams. The stiffness of beams was accurately estimated from the noisy sensed force using the model, with higher accuracy for smaller noise. Then, the model predicted contact forces and mechanical energetic cost to plan and control the simulation robot to traverse beams with a lower cost. The simulation robot pushed cross flimsy beams and rolled through stiff beams just like cockroaches do. At last, we demonstrated this sensing and estimation in a robotic physical model. |
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