Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session M38: Robophysics IV |
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Sponsoring Units: DBIO DSOFT Chair: Benjamin McInroe, University of Pennsylvania Room: 103D |
Wednesday, March 6, 2024 8:00AM - 8:12AM |
M38.00001: Revisiting resonance in flapping flight: Supra-resonant oscillations in moths, bees, and robophysical models Simon N Sponberg, Ethan Wold, Ellen Liu, Jeffrey F Gau, James E Lynch, Nick G Gravish Most insects fly with indirect actuation using muscles acting in parallel to elastic exoskeletons and coupled in series to flapping wings. This combination results in resonant dynamics even if it differs from classic viscoelastic oscillators because of the presence of structural (frequency-independent) damping and aerodynamic drag. Moreover, muscle force can periodically drive wingstrokes (termed synchronous flight) or incorporate stretch activation resulting in self-excited, limit-cycle oscillations decouple from neural pacing (asynchrony) or be a combination of the two. Yet while insects have resonant mechanics, do they operate at their resonant frequency? And what are the different implications for periodically forced and self-excited flapping flight especially when both types of forcing are present? Here we show that synchronous hawkmoths and asynchronous bumblebees are both supra-resonant, operating above their kinematic resonance peak. We explore these properties in a dynamically scaled spring-wing robotic flapper whose kinematics are emergent. Spring-wing systems with both types of forcing can transition from one mode of flight to the other across a classic entrainment boundary. Operating off-resonance does not preclude useful energy exchange but sets up a trade-off of power reduction and control via frequency modulation. We capture this tradeoff in the nondimensional Weis-Fogh number, n, the ratio of peak inertial to peak aerodynamic force, which is 1-10 for nearly all insects. |
Wednesday, March 6, 2024 8:12AM - 8:24AM |
M38.00002: Directional take-off and aerial control of ultrafast jumps in springtails and robots Jacob Harrison, Adrian Smith, Hungtang Ko, Baekgyeom Kim, Jesung Koh, Saad Bhamla Spring-latch mechanisms are found in biological and engineered systems to achieve accelerations greater than what direct motor or muscle actuation can achieve. However, once the latch is released in these mechanisms, controlling the flow of elastic energy to modulate dynamic outputs is a challenge. Here we show certain species of springtails include an elastic hinge in their furca, a jumping appendage, that bends during a jump, affecting their take-off and jump dynamics. Springtails are a group of small, non-insect hexapods that use ultrafast jumps to evade predators, disperse in their environment, and even migrate. We investigate how furca morphology and kinematics affect the jump dynamics across species of springtails and whether including passive elastic elements in mathematical and physical models shows increased control of ultrafast movement. We analyzed the takeoff kinematics across several species of springtails leaping off rigid and compliant substrates. Results show that some species with longer furcas bend the furca during a jump, these species have lower take-off angles and have less body spin than species with long, rigidly held furcas. We use mathematical and robophysical modeling to explore whether including a joint is sufficient to reduce take-off angles and angular velocity. Our findings offer novel insights into how ultrafast biological systems control their jumps and inform potential constraints on the flow of elastic energy through materials at millisecond timescales. |
Wednesday, March 6, 2024 8:24AM - 8:36AM |
M38.00003: Creating a robophysical model to study how malaria infiltrates human skin Kyungmo Choi, Shruthika Kandukuri, Yaqing Wang, Yun Chen, Chen Li Malaria remains a serious health concern worldwide, especially in developing countries. Understanding how malaria parasites (sporozoites) infiltrate skin (a complex matrix of collagen fibers immersed in water) to reach bloodstreams will facilitate the cure for the disease. However, it is challenging to understand the complex interaction between the elongate organism and the complex environments, as the equations of motion are too complicated to solve directly. Here, based on recent biological observations, we created a robophysical model that mimics the movement of sporozoites along collagen fibers. We designed and manufactured a segmented robot to model a sporozoite and used elastic rods immersed in a viscous fluid (with Reynolds number matched to the biological system) to model collagen fibers in skin. The robot's segments has actuated wheels to allow it to crawl on the rod. Additionally, to replicate the sporozoites' curved shape and enable steering, the segments are daisy-chained with cables on both sides which can be shortened by motors. We will use this robophysical model to study how sporozoite locomotion varies with its mechanical properties and actuation and the parameters of the environment. This will provide a ground truth for future computational modeling. |
Wednesday, March 6, 2024 8:36AM - 8:48AM |
M38.00004: Fiber-Robot with Adjustable Electrodes for Long Term Neural Recording Jacob Pelster, Itai Cohen, Xiaoting Jia, Yujing Zhang, Alexander Parrott, Qingkun Liu, Hengji Huang, Jongwoong Kim Multi-electrode neural recording methods, such as the design of the popular Michigan electrode, allow multi-location, multi-neuron recording. Such electrodes consist of metal pads situated on a rigid surface, inserted into the brain. The electrodes are positioned to achieve the best signal; however, with a rigid substrate, it is impossible to optimize all signals. Additionally, after insertion glial scarring and neural migration can change the signal. We present, in collaboration with Virginia Tech, a prototype of a novel fiber-robot probe, with individually controllable electrode arms - capable of moving through gels with mouse brain modulus, which will be able to detect and position the arms in the best location for neural sensing. The device consists of a thermally drawn fiber, containing sense and actuate signal wires, developed by Virginia Tech, bonded to an actuating base, utilizing the Cohen group's scalably strong palladium bulk electrochemical actuators. With a fabricated prototype, initial testing in agarose gel of applicability of electrode as a neural sensor, the robot's strength, and electrical tracking ability will be presented. |
Wednesday, March 6, 2024 8:48AM - 9:00AM |
M38.00005: Towards a computational toolbox for resolving the multiscale dynamics of animal and robot behavior Benjamin McInroe, Daniel E Koditschek, Robert J Full, Yuliy Baryshnikov The complexity of animals' and robots' coupled, nonlinear hybrid (contact-making and -breaking) dynamics can be mitigated by postulating that agile behaviors arise from composition of favorable postural subspaces within which constituent tasks are encoded as "templates" (low degree of freedom dynamical abstractions) and down toward which the high degree of freedom body and limbs are "anchored" (quickly controlled to converge). To take the next step towards discovery of the template representations that enable agile animal locomotion, we developed a computational pipeline that extracts such low dimensional attracting invariant postural submanifolds from high dimensional trajectory data. Growing evidence from robotics suggests the utility of hierarchical compositions whereby spatially active bodies anchor sagittal plane templates, which, in turn, anchor still lower dimensional cycles whose postural loci within the plane determine the abstract behavioral pattern, for example, the difference between bounding, trotting or pronking. This talk will discuss our recent work refining the selection of pipeline parameters suitable for resolving such nested multiscale hierarchical compositions. |
Wednesday, March 6, 2024 9:00AM - 9:12AM |
M38.00006: Drag forces on objects moving on elastically deformable membranes Hussain N Gynai, James K Lewis, Shengkai Li, Daniel I Goldman To develop a resistive force theory (RFT) type model of the dynamics of a wheeled vehicle locomoting on a deformable spandex membrane (discussed in Li et al., PNAS, 2022), we investigate drag forces on a wheel moving at constant speed across the surface. We are interested in how the parallel and perpendicular components of the drag differ (i.e., anisotropy) and depend on the speed as well as the angle of attack, the angle between velocity and orientation of the wheel. We use a robot arm to drag a fixed and a freely rotating wheel (4 cm in diameter) across the membrane at varying speeds (1 to 50 cm/s) and angles of attack (0 to 90 degrees) while monitoring drag force components (perpendicular and parallel to the wheel axis) and their magnitudes. Experiments reveal that the fixed wheel's drag exhibits a sublinear dependence on speed. For speeds greater than 30 cm/s, drag forces fluctuate due to stick-slip-type motion, where the membrane wrinkles and bunches under the wheel. The rotating wheel experiences speed-independent drag for zero angle of attack and rate-dependent drag forces for non-zero angle of attack. The fixed wheel's drag force is linear with the angle of attack in the parallel and perpendicular directions. The drag force on the rotating wheel remains small until a 60-degree angle of attack. between 60 and 80 degrees, the drag force starts to fluctuate due to stick-slip-type motion. For attack angles greater than 80 the parallel drag drops to zero, and the perpendicular drag becomes steady and non-zero. |
Wednesday, March 6, 2024 9:12AM - 9:24AM |
M38.00007: Finding tradeoffs in muscle types through a robophysical model of the Hill muscle Jake E McGrath, José R Alvarado Muscles are biology's actuators: muscle's ability to generated force and do work ultimately allows organisms to navigate their environments and search for food. Studying the mechanical state properties (i.e., force generation, rate of contraction, power output) of muscle and different muscle types, therefore, is critical in understanding how life persists. Studying muscle in-vivo, however, remains a long-standing challenge: real-time data collection of muscle's mechanical state properties is incredibly invasive and difficult to do. Here, using feedback control and a DC motor as our actuator, we create a robophysical model of the Hill muscle. The Hill muscle describes the nonlinear relationship between a muscle's contraction rate and force generation where the degree of nonlinearity is parametrized by a nondimensional α. With our muscle-mimicking actuator, we can measure real-time mechanical state properties and the energetic inputs required for actuation. Moreover, we can systematically test an array of different muscle types parameterized by α and assign an efficiency of actuation. We establish a scalar power characteristic defined as the area under an actuator's force-velocity curve: it is a property of all actuators and indicates an actuator's ability to do work. Using the power characteristic as a basis, we find a tradeoff in muscle types: muscles that are nearly linear in force-velocity space are optimized for power output whereas highly nonlinear muscles are optimized for energy efficiency. |
Wednesday, March 6, 2024 9:24AM - 9:36AM |
M38.00008: Lightweight Autonomous Crawling Robot Utilizing Vacuum-Driven Self-sensing Origami Actuators for 3D Multi-Terrain Exploration Jiaqi Wang, Xiaohao Xu, Jonathan Mi, Wenzhe Tong, Xiaonan Huang Despite tremendous progress in the development of untethered soft robots in recent yeas, autonomous untethered pneumatic robot continue to confront multifaceted challenges. These encompass the hardware integrations, meticulous pressure regulation, ground-wall-ceiling transition and real-time SLAM and motion planning in unstructured environments. This research presents a novel lightweight, autonomous crawling robot, equipped with trio parallel 3D-printed Kresling origami actuators. On the hardware, this robot cohesively integrates power and control modulars, vision systems, pneumatic systems, and angle sensors. In lower-level control, the robot leverages the contraction-twisting coupled folding characteristics of the Kresling origami pattern, realizing the robot's state propriocetion. In high-level control, the robot employs a camera for simultaneous localization and mapping, by remotely controlling and transmitting real-time images wirelessly, guiding subsequent gait planning. Experimental results demonstrate the robot's abilities of transitioning locomotion, autonomous navigation in multi-terrains, and a range of environmental exploration tasks. |
Wednesday, March 6, 2024 9:36AM - 9:48AM |
M38.00009: Decoding frequencies generated during spider vibration sensing through robophysical modeling Eugene Lin, Yishun Zhou, Luke Moon, Andrew Gordus, Chen Li Orb-weaving spiders detect web intruders through vibration sensors in their legs. They have been observed to assume different leg postures and repeatedly crouch their legs during vibration sensing. This behavior is hypothesized to be a form of active sensing—by modulating the vibration dynamics of the spider-web-target system, the spider may better detect prey. However, whether this is true and how it works is poorly understood due to challenges in measuring the whole system's vibration dynamics with actively behaving spider and prey. Here we developed a robophysical model of the spider-web-prey system. We measured the resulting vibrations of the web and the spider robot's legs, when the spider robot and/or the prey robot were actuated at various frequencies. In all scenarios, actuation of either the spider robot, the prey robot, or both induced an added frequency component to the web vibration, which likely corresponds with the spider-web-target systems' natural frequencies. We hypothesize that this added frequency component can be modulated by the legs to enhance sensing. We are performing further experiments and developing a dynamic simulation to better understand how both robots' behaviors influence this component to better understand active vibration sensing on the web. |
Wednesday, March 6, 2024 9:48AM - 10:00AM |
M38.00010: Understanding the buckling instability in jumping nematode and inspired soft model Sunny Kumar, Ishant Tiwari, Victor M. Ortega Jimenez, Adler Dillman, Saad Bhamla Nematodes are abundant in most ecosystems, playing a pivotal role in soil health and nutrient recycling. In these environments, they primarily exhibit behaviors such as swimming and crawling locomotion. A few nematode parasites of insects in the genus Steinernema possess the ability to leap toward the host. During the jumping process, these entomopathogenic nematodes (S. carpocapsae) form an alpha shape with capillary latch and upon reaching their buckling limit, a kink configuration enables them to achieve high-velocity jumps (~10 bodylength/s). In this study, we designed a soft jumping model by drawing inspiration from nematode leaping using buckling, which showed similar jumping behavior and performance. We explored various parameters such as aspect ratio, kink instability, and the effect of moduli on jumping capabilities. By combining these biological insights with engineering principles, a soft jumping mechanism is devised, holding the potential to offer opportunities for soft limbless locomotion and actuators. |
Wednesday, March 6, 2024 10:00AM - 10:12AM |
M38.00011: Nonlinear, muscle-like actuation reduces energy consumption— does it also simplify control? José R Alvarado, Jake McGrath, Brian Kent Organisms convert chemical energy to mechanical work, allowing them to perform a wide range of impressive mechanical tasks. The most common organ that performs this kind of conversion is muscle. Seminal work by Hill demonstrated that muscle is inherently nonlinear, with a hyperbolic force-velocity relation. This is in stark contrast to electromagnetic motors— common actuators in household appliances and robots— which have linear properties. What are the mechanical advantages of nonlinear actuation? Answering this question is difficult, because force-velocity relations of living muscle cannot be systematically varied. Here, we seek to answer this question with "HillBot", a robot that lifts a weight against gravity while mimicking muscle's nonlinear force-velocity relation using feedback control. We systematically vary a parameter, α, that controls nonlinearity. Even after accounting for the lower power characteristic of high-α actuators, we find that increasing α decreases energy consumption. We predict that nonlinear actuation determines a tradeoff between economy and performance. We furthermore hypothesize that nonlinearity improves robustness to perturbation and simplifies the computational burden of neuromuscular control. |
Wednesday, March 6, 2024 10:12AM - 10:24AM |
M38.00012: Nonlinear Dynamics of Sound Detection in the Auditory System Dzmitry Vaido, Martín A Toderi, Dolores Bozovic The auditory system can detect displacements as small as 3 Å and frequencies as high as 200 kHz. Significant evidence indicates that it achieves this sensitivity by active amplification performed by the sensory cells. Furthermore, its highly nonlinear response has characteristics that are well captured by equations based on the Hopf bifurcation. The study of auditory detection therefore poses a problem at the intersection of nonlinear dynamics with out-of-equilibrium physics. To understand the mechanisms behind this remarkable sensitivity, we are exploring the dynamics of hair cells – the sensory receptors of the auditory system. In this study, we develop a robust in vitro preparation of an auditory organ (amphibian papilla) and observe spontaneous and driven oscillations of hair bundles. The preliminary data has shown a large variation in the character of spontaneous oscillations in amphibian papilla, including a range of amplitudes and frequencies, varying levels of noise, bursting behavior, and other phenomena, indicating that multiple bifurcations may characterize the underlying dynamics. Measurements obtained from individual hair cells show they phase lock to extremely weak signals and exhibit a compressive nonlinearity similar to in vivo observations. In the future, we plan to further explore the nonlinear dynamics of the auditory system, as well as to address the frequency tuning and tonotopy of amphibian papilla. |
Wednesday, March 6, 2024 10:24AM - 10:36AM |
M38.00013: A Mechanical Origin of Cooperative Transport Matan Yah Ben Zion From humans hauling an oversized sofa to ants foraging a large leaf, cooperative transport is commonplace. However, achieving cooperative transport by design remains a great challenge for physicists, mechanical engineers, and roboticists. In my talk, I will present the ``transporton'', a new kind of self-propelled particle whose mechanical design gives rise to a novel dynamical response: when subjected to an external force, a transporton aligns and propagates in a direction opposite to the force. This unique force response allows these active particles to spontaneously coordinate the transport of a much larger payload. The force alignment is captured by an effective, charge-like parameter of a self-propelled particle. This effective parameter is signed and has units of curvature. We show in experiments and simulations that robots with a negative active charge push against an external payload, leading to transport, without relying on complex circuitry, sensors, or communication. Surprisingly, we find that transport increases with increasing payload size. We derive an analytical criterion for transport and find it has a geometrical origin as the interplay of two curvatures --- the payload's shape and the effective charge-like parameter. Our findings generalize existing models of self-propelled particles and offer new design rules for distributed robotic systems, potentially shedding light on cooperative transport in natural swarms. |
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