Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S64: Robophysics: Robotics Meets Physics IUndergraduate
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Sponsoring Units: DBIO Chair: Chen Li, Johns Hopkins University Room: BCEC 259B |
Thursday, March 7, 2019 11:15AM - 11:27AM |
S64.00001: Importance of body and leg adjustment for traversing cluttered terrain Yaqing Wang, Ratan Sadanand Othayoth Mullankandy, Chen Li Although robots are good at avoiding obstacles, in critical applications like search and rescue in cluttered terrain like earthquake rubble, they must traverse obstacles using effective physical interaction, an ability still missing from most robots. Here, we study how the ability to adjust body parts and legs contributes to cluttered terrain traversal using animal and robophysical experiments. To traverse grass-like beams, cockroaches adjusted their head, body, abdomen, and legs in coordination. As the animal pushed against the beams, its body pitched up due to terrain interaction. In response, the animal flexed its head repeatedly to reduce body pitching and physically feel out the terrain. In addition, the animal used two hind legs differentially, extending and depressing one more than the other (P < 0.05, ANOVA), to roll its body to align with the gap between beams to reduce terrain resistance. Finally, the animal pushed the lower hind leg backward on the ground to propel itself forward while flexing its abdomen to break body rubbing against beams. We developed a robot with the ability to flex its head and abdomen and differentially move its legs and used it as a physical model to study the principles of using reactive motions to modulate physical interaction to traverse. |
Thursday, March 7, 2019 11:27AM - 11:39AM |
S64.00002: JUMP: Experiment-enabled Modeling of Click Beetle Jumps for Robotic Applications Ophelia Bolmin, Lihua Wei, Jake J Socha, Marianne Alleyne, Alison Dunn, Aimy A Wissa Click beetles use a unique jumping maneuver to self-right without using their legs. The jump is power-amplified thanks to a hinge situated in the thoracic region. The hinge is composed of a peg and a mesosternal lip, two conformal parts that allow the body to be locked in an arched position before the energy-release phase, which results in a jump. The jump of the beetles is divided into three stages: the pre-jump (latching), take-off (snapping), and airborne (jump) stages. In this paper, we present data extracted from synchrotron x-rays experiments at Argonne National Laboratory. High-speed video recordings (1,000 – 30,000 fps) show the latching phase, the contraction of soft cuticle prior to energy release, and the quick snapping maneuver. To describe the latching and snapping phases of the jump, we integrated experimental and morphological data into new analytical models. A combined mechanical/friction model predicts the initiation of slip between the peg and lip, and a dynamic force analysis model calculates the center of mass accelerations and required torques at the hinge. Understanding the enabling physics of the three jump stages creates numerous opportunities for engineering applications including self-righting robots and power-amplifying actuation systems. |
Thursday, March 7, 2019 11:39AM - 11:51AM |
S64.00003: A Robophysical Analysis and Gait Development for the NASA Resource Prospector Rover Siddharth Shrivastava, Andras Karsai, Yasemin Ozkan aydin, Veronica Paez, William Bluethmann, Robert O. Ambrose, Daniel Goldman Planetary rovers can become entrapped in soft substrates. The LCROSS lunar mission in 2009 indicated that regolith was less consolidated at the lunar poles than the equator. This led NASA JSC to develop RP-15, a 300 kg rover capable of lifting and sweeping each wheel to develop a crawling behavior. To discover techniques to improve performance, we created a scaled (2.1 kg) robophysical rover, conducting systematic experiments in our autonomous tilting, aerating, and motion capture gantry apparatus. A combination of stepping and wheel rolling produced higher drawbar-pull than wheel rotation alone in any situation (~4x increase on a 0o poppy incline). We validated our findings through experiments on RP-15 at JSC (~2x on a 0o sand incline). On steeper slopes (up to 27o, near max angle of stability), a novel gait generated forward progress via terrain remodeling via controlled avalanches. Rolling front wheels led to substrate mound formation posterior to the rover with stepping/paddling hind wheels generating forward progress; the wheel-only and walking-only gaits led to backward progress. Single paddling/rolling wheel force measurements showed a 2x increase in normal force per gait cycle over pure rolling. Our discoveries generalize to weakened (via aeration) and wet granular media. |
Thursday, March 7, 2019 11:51AM - 12:03PM |
S64.00004: Micro and nanorobots propelled by science Johannes Sachs, Peer Fischer Nature has evolved many microorganisms that operate without neurons, yet exhibit remarkably complex behaviors. These are examples of autonomous machines whose function and interaction with the environment is entirely governed by the chemistry and physics at small scales. Since consciousness plays no role, there is thus no fundamental reason why we should not also be able to build and operate analogous synthetic microrobots. One key ingredient is the ability to synthesize and engineer complex 3D parts and ways to organize or assemble these components. Another challenge is to provide energy for activation, which calls for strategies that are entirely different to the many engineering solutions that have been devised at large scales. This talk will describe our efforts in realizing such systems – some with outside control, others that are entirely autonomous – at the smallest of scales. |
Thursday, March 7, 2019 12:03PM - 12:15PM |
S64.00005: Kirigami pop-up spikes improve soft robot anchoring and locomotion under soil Bangyuan Liu, Yasemin Ozkan aydin, Daniel Goldman, Frank L Hammond III
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Thursday, March 7, 2019 12:15PM - 12:27PM |
S64.00006: The use of robophysical mantis shrimp models to study ultra-fast "impulsive" biological an synthetic systems Emma Steinhardt, Rob J Wood Peacock mantis shrimp are considered the fastest strikers in the animal kingdom, achieving punches in the range of 14-23 m/s in water – fast enough to create cavitation bubbles and break clam shells. They accomplish this with a dactyl heel striking appendage only a few centimeters long. In order to study these remarkable capabilities, we leverage recent breakthroughs in multi-scale, multi-material rapid fabrication to create a physical model of the mantis shrimp at scale. The rapid release of energy storage is accomplished through a torque reversal mechanism with a spring in parallel. Our preliminary design is capable of achieving a 15.5 m/s peak velocity, 67.4% the peak velocity of biological mantis shrimp. We’re able to demonstrate the formation of cavitation bubbles in striking, and can produce peak forces of 100 N. Our analytical dynamic model is capable of accurately predicting the trajectory and peak velocities of our current design. We will present designs using our model that maximize velocity. Our simulation results will be accompanied by our experimental results for various fluid loads and design parameters. These results will then be used to inform us on how the biological system operates and how the underlying physics contribute to its performance. |
Thursday, March 7, 2019 12:27PM - 12:39PM |
S64.00007: Coordination of legs and body undulation during turning in quadruped locomotion Baxi Chong, Yasemin Ozkan aydin, Guillaume Sartoretti, Jennifer Rieser, Haosen Xing, Chaohui Gong, Howie Choset, Daniel Goldman Sprawled-postured quadrupeds like lizards and salamanders must coordinate limb with body movements to adjust their direction of motion while walking in environments with obstacles. However, their robotics counterpart, the quadrupedal robots, often rely on adjusting their direction of motion by introducing a lateral asymmetry in leg motion amplitude, making the stable transition between forward and turning gaits difficult. We hypothesize that using properly-coordinated body undulation and limb movements will enable effective locomotion and stable transitions between gaits. Using geometric mechanics, we design gaits by prescribing a footfall pattern and optimizing the body undulation which produces a desired motion. We predict that rotations resulting from coordination of body undulation and limb movements can simplify gait transitions in legged robots, and we verify our predictions by measuring displacements and rotations of a robophysical quadruped locomoting through granular media. We find that the amplitude of body undulation controls the steering angle, and thus controls the turning radius. In particular, we find that by increasing the body undulation amplitude from π/12 to π/8, the turning radius decreased from 10.5±0.3 body lengths (BL) to 2.9±0.1 BL. |
Thursday, March 7, 2019 12:39PM - 12:51PM |
S64.00008: Robophysical Investigation of Root Circumnutation through Heterogeneous Environment Mason Murray-Cooper, Yasemin Ozkan aydin, Enes AYDIN, Nicholas Naclerio, Erin N McCaskey, Jennifer Rieser, Elliot Hawkes, Daniel Goldman Circumnutation, a cyclic endogenous circular pattern exhibited by the tip of a growing root, occurs in a diversity of plants, but its function is not fully understood. To investigate the hypotheses that such motion facilitates substrate penetration and exploration, we built a planar soft robot [Hawkes et al. 2017], which grows from the tip like a plant root and can bend in 2D space by oscillating inflation of the series pneumatic artificial muscles (sPAMs) arranged on the two sides. Existing work observed force reduction effects from circumnutation in homogeneous granular material [Dottore et al. 2016]. Here we demonstrated that tip oscillation aids the robot to penetrate heterogeneous environment, e.g. hard obstacles, by growing the robotic root into a lattice of rough cylinders (d=8cm) distributed uniformly on a board (120X120cm^2). Systematic variation of initial robot positions revealed that the non-oscillating tip strategy led to an increased probability to become pinned to obstacles and unable to grow more than 23.8±19.7cm; the oscillating tip penetrated the lattice significantly further, 55.2±24.9cm. The results show that without complicated control and sensing mechanism, oscillatory movement of a growing structure enables robust navigation in a heterogeneous environment. |
Thursday, March 7, 2019 12:51PM - 1:03PM |
S64.00009: Avian-Inspired Devices for Improved Mission Adaptability in Unmanned Aerial Vehcles Aimy Wissa, Chengfang Duan, Mihary Ito There are significant efforts underway focusing on understanding the physics of avian flight. There is also increasing need for small unmanned aerial vehicles (UAVs) to conduct a variety of civilian and military mission scenarios. This paper starts by showing that avian-inspired flight has the potential to combine desired flight capabilities of hovering, maneuverability, agility, safety, and stealth in UAVs. The concept of wings as multifunctional adaptive structures is discussed and several flight devices found in birds’ wings are introduced as a pathway towards revolutionizing the current design of small UAVs. These devices include adaptive wing tips for increased agility, covert-inspired deployable structures and alula-inspired leading edge devices for stall mitigation and separation control. Experimental, analytical, and numerical results are presented to show the feasibility of adapting these devices to engineered vehicles. The experimental studies conducted on the engineered systems also provide insights into the physics of the living systems and can be used to increase the current understanding of the morphology and function of these devices in nature. |
Thursday, March 7, 2019 1:03PM - 1:15PM |
S64.00010: Soft landing of a legged robot on yielding terrain Daniel Lynch, Paul Umbanhowar, Kevin Lynch Many robotics applications where legged robots are preferable to wheeled or treaded robots feature yielding terrain. While legged locomotion on rigid ground is non-trivial, yielding terrain presents additional challenges such as permanent ground deformation, and dissipative effects. Regardless of substrate, successful legged locomotion entails starting, maintaining, and stopping a gait. We specifically address the challenge of terminating the hopping gait of a simple single-leg robot on soft ground while minimizing foot penetration depth, a locomotion primitive we call a “soft landing.” Using analytical methods from optimal control theory, we find that the penetration-minimizing feedforward control program is a bang-bang controller, followed by a third constant-force segment. While this control is optimal given our formulation of the soft landing problem, it is sensitive to model uncertainty and timing errors. Consequently, we also compare the robustness to terrain uncertainty of the optimal feedforward control to a biologically-inspired virtual impedance controller. |
Thursday, March 7, 2019 1:15PM - 1:27PM |
S64.00011: Running up a sand dune Brian Chang, S. Tonia Hsieh Running up a sand dune is a challenging task due to several factors. First, sand fluidizes when an external force exceeding the material yield stress is applied. Second, at the angle of repose, the sand pile is in a metastable state, such that small perturbations will cause fluidization. Ongoing studies show that sand specialist lizards exhibit lower performance decrements than desert generalist when running up inclined sand. Preliminary evidence suggests that these differences are largely correlated with different impact angles of the feet relative to the sand, indicating that differences in foot movement can have dramatic effects on running ability. In this study, we experimentally examine the vertical impact force of a flat plate (1 in x 1 in) against a glass beads with varying plate and substrate angles. The plate impacted the substrate at 0.6 m/s with a force sensor attachment. Here, we find that impact at higher angles reduces the peak force, with impacts at the angle of repose producing 55% less force compared to impacts on a flat bed. Greater substrate incline also increases the time to reach the peak force. This is largely due to earlier contact time which causes the sand to fluidize sooner. Results from impacts with different plate angles will also be discussed. |
Thursday, March 7, 2019 1:27PM - 1:39PM |
S64.00012: Randomness in appendage oscillations helps a robot self-right Qihan Xuan, Ratan Sadanand Othayoth Mullankandy, Chen Li Uncertainty is usually avoided or mitigated in control of robot locomotion. When flipped over, the winged discoid cockroach rights itself by repeatedly opening and closing its wings to push against the ground and flailing its legs, both with substantial randomness. A cockroach-inspired robot also uses coupled oscillations of wings and a tail-like appendage (mimicking flailing legs) to self-right but is well controlled. Can randomness be used to improve performance? Here, we test this idea using an experimentally validated multi-body dynamics simulation of the robot. As appendage oscillation randomness (coefficient of variation) increased from 1% typical of the well-controlled robot to 20% typical of the animal, the robot self-righted more often (43% vs. 69%) and more quickly (6.8 ± 3.9 s vs. 5.2 ± 3.8 s) (P < 0.001, ANOVA). We discovered that an appropriate phase offset between the two oscillations was critical to self-righting. Periodic oscillations limited the coupled-oscillator system to visiting only a few phase offsets, causing it to often be trapped near failure limit cycles. Added randomness in appendage oscillations allowed the system to explore more phase offsets, increasing probability and reducing time to escape from failure limit cycles and self-right. |
Thursday, March 7, 2019 1:39PM - 1:51PM |
S64.00013: The stigmatic-start: a rapid non-planar gait in snakes Nicholas Charles, Raghunath Chelakkot, Bruce Young, Mattia Gazzola, L Mahadevan Newborn and juvenile yellow anacondas exhibit a previously unreported rapid transient gait, which we term the stigmatic-start. This is characterized by the snake first bending its body and then lifting itself partly out of the plane while moving forward about the mid-section. While superficially similar to sidewinding, the stigmatic-start is qualitatively different as it is a very rapid transient gait that allows the snake to move parallel to itself. To understand our observations, we construct a mathematical model for the non-planar locomotion of snakes that shows an interesting gait transition as a function of body size; small (juvenile) snakes can move via stigmatic locomotion but large (adult) snakes cannot, just as seen. In the context of biomimetic applications, the simulations of our model also suggest an avenue for optimal control of soft active filaments. |
Thursday, March 7, 2019 1:51PM - 2:03PM |
S64.00014: Towards Obstacle-aided Legged Locomotion in Cluttered Environments Feifei Qian, Divya Ramesh, Daniel E Koditschek Modern robots are often required to perform tasks in environments filled with obstacles and disturbances. However, most legged platforms are not yet capable of coping gracefully with unanticipated repeated disturbances, and often rely on active sensing to avoid all engagements with their physical surroundings. In this study, we propose a novel framework wherein we abstract the obstacle-cluttered environment into a horizontal-plane disturbance force field, and we consider robot legs as disturbance selectors. With different gait patterns, the robot can generate different disturbance forces on its center-of-mass from the same physical environment. Our simplified model significantly reduces the complexity of representing interactions between robot and obstacle-cluttered environments, and begins to suggest an approach to using gait space affordances for purposes of generating desirable obstacle responses in multi-legged robot locomotion amidst complex environments. |
Thursday, March 7, 2019 2:03PM - 2:15PM |
S64.00015: Mechanics of snake slithering on deformable substrates. Perrin Schiebel, Jennifer Rieser, Henry Astley, Alex M Hubbard, Kelimar Diaz Cruz, Daniel Goldman Elongate, limbless animals like snakes move in both fluid and terrestrial habitats using flexural waves of the body. Little is known about their movement in materials like mud and granular matter (GM) which provide propulsion while yielding but, unlike fluids, may be permanently deformed by the interaction. We studied the ~40 cm long desert-dwelling snake C. occipitalis slithering on the surface of homogeneous GM. The snakes traveled 30-80 cm/s using a stereotyped shape. Surface drag measurements revealed that the ratio of thrust to drag forces, a critical component in undulatory motion, did not depend on speed or depth. We developed a surface resistive force theory (RFT) which revealed their waveform maximized center-of-mass speed given a constraint on peak muscle power. The snakes’ motion was non-inertial, so we explored the performance of a robophysical model, a 10-link 70 cm long robot snake. The waveforms RFT predicted would maximize the speed of the robot instead failed to make progress, largely because the robot would re-encounter previously disturbed material. The snakes’ waveform was in the regime where motion is like that in a frictional fluid; by limiting material yield the animal avoided contending with the memory-dependent effects that stymied the robot. |
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