Bioinspiration & Biomimetics

Aquatic organisms often employ maneuverable and agile swimming behavior to escape from predators, find prey, or navigate through complex environments. Many of these organisms use metachronally coordinated appendages to execute complex maneuvers. However, though metachrony is used across body sizes ranging from microns to tens of centimeters, it is understudied compared to the swimming of fish, cetaceans, and other groups. In particular, metachronal coordination and control of multiple appendages for three-dimensional maneuvering is not fully understood. To explore the maneuvering capabilities of metachronal swimming, we combine 3D high-speed videography of freely swimming ctenophores (Bolinopsis vitrea) with reduced-order mathematical modeling. Experimental results show that ctenophores can quickly reorient, and perform tight turns while maintaining forward swimming speeds close to 70% of their observed maximum -- performance comparable to or exceeding that of many vertebrates with more complex locomotor systems. We use a reduced-order model to investigate turning performance across a range of beat frequencies and appendage control strategies, and reveal that ctenophores are capable of near-omnidirectional turning. Based on both recorded and modeled swimming trajectories, we conclude that the ctenophore body plan enables a high degree of maneuverability and agility, and may be a useful starting point for future bioinspired aquatic vehicles. Author summaryMetachronal swimming--the sequential, coordinated beating of appendages arranged in a row-- exists across a wide range of sizes, from unicellular organisms (micrometers) to marine crustaceans (tens of centimeters). While metachronal swimming is known to be scalable and efficient, the level of maneuverability and agility afforded by this strategy is not well understood. This study explores the remarkable 3D maneuverability of ctenophores (comb jellies), and the appendage control strategies they use to achieve it. Ctenophores have eight rows of appendages (instead of the one or two found in crustaceans and other organisms). This higher number of appendages, their distribution along the body, and the independent frequency control between paired rows enables near-omnidirectional swimming and turning performance, placing ctenophores among the most maneuverable swimmers. We use experiments and mathematical modeling to explore both the real and theoretical performance landscape of the ctenophore body plan, and show that ctenophores are capable of executing tight turns at high speeds in nearly any plane. This omnidirectional swimming capability gives insight into the ecology and behavior of an important taxonomic group, and shows the potential of metachronal swimming as a source of design inspiration for robotic vehicles (particularly those that must navigate complex environments).

Despite the extreme flexibility of the octopuss arms and their resulting near infinite possible configurations, the octopus effectively controls its arms during a wide variety of behaviors, including locomotion, foraging, excavation, exploration, and manipulation. If appropriately characterized, the octopuss biomechanical properties and control strategies could be implemented in the development of a soft robotic limb with the same range of capabilities. When operating without visual feedback, the octopus must rely on the complex chemotactile sensory system within its suckers, and in these conditions sucker recruitment plays a prominent role in search behavior, causing the arm to conform to surface features in the environment. However, how this mechanism is used to search over the complex and convoluted surfaces in the octopuss natural habitat is unknown. Here, we investigate the strategies the octopus uses to search for a reward hidden among a row of multiple small openings of a task space, and how it uses multiple arms to search three parallel versions of this task space. We found that when the arm encounters multiple openings in a surface, it performs a distal to proximal search pattern, starting with the farthest openings within reach then working its way proximally with a preference for searching each opening in succession. This strategy would allow the octopus to use its highly flexible limbs to perform an exhaustive search pattern over complex surfaces.

In this paper,we consider the feasibility of mimicking the sprawling gait of a live varanid (Varanus salvator) using a necrobot (named: Pak Biawak), a robot constructed using the skeletal parts of a deceased varanid of the same species. Pak Biawak is manufactured using simple joints and components, and limb motion is coupled to passive spine bending to enable the sprawling gait. Here, we assess both the lateral and dorsal kinematics of Pak Biawak at different speeds, and compare the metrics from each to those of a similarly sized live varanid. When assessing lateral view shape metrics (stride aspect ratio, stride circularity, normalised stride swept area, normalised stride swept area perimeter), we find that Pak Biawaks gait is consistent across all speeds and the majority of Pak Biawaks lateral shape metrics are kinematically aligned with those of the live varanid. This also proves true when comparing Pak Biawaks lateral trajectory metrics (radial distance of swept area, normallised root mean squared error) against those of the live varanid, and at different speeds of sprawling. Pak Biawaks dorsal metrics include the spine bending amplitude and period, and these are not found to be significantly different to those of the live varanid, however, Pak Biawaks amplitude is affected by sprawling speed. We use three metrics to compare forward and reverse limb sweeps including, angular curvature, differential curvature, and a normalised arc length. Of these, a preponderance of highly significant differences (p[≤] 0.001) are observed on comparing the forward sweep arc length of Pak Biawak at every sprawling speed against the forward sweep arc length of the live lizard. All other kinematic metrics in the necrobot are nevertheless very close to those of the live lizard. Finally, when comparing the trackway width of Pak Biawak against the live lizard, we again find there is very close kinematic compatibility between the two, and conclude that our necrobot can be designed and manufactured to mimic the sprawling gait of a real varanid, even when using simple kinematic linkages in unison with a passive spine bending differential applied at only one central location in the necrobot spine.

How animals jump and land on a variety of surfaces is an ecologically important problem relevant to bioinspired robotics. We investigated this topic in the context of the jumping biomechanics of the planthopper Lycorma delicatula (the spotted lanternfly, SLF), an invasive insect in the US that jumps frequently for dispersal, locomotion, and predator evasion. High-speed video was used to analyze jumping by SLF nymphs from take-off to impact on compliant surfaces. These insects used rapid hindleg extensions to achieve high take-off speeds (2.7-3.4 m/s) and accelerations (800-1000 ms-2), with midair trajectories consistent with zero-drag ballistic motion without steering. Despite rotating rapidly (5-45 Hz) in the air about time-varying axes of rotation, they landed successfully in 58.9% of trials; they also attained the most successful impact orientation significantly more often than predicted by chance, consistent with their using attitude control. Notably, these insects were able to land successfully when impacting surfaces at all angles, pointing to the emerging importance of collisional recovery behaviors. To further understand their rotational dynamics, we created realistic 3D rendered models of SLFs and used them to compute their mechanical properties during jumping. Computer simulations based on these models and drag torques estimated from fits to tracked data successfully predicted several features of their measured rotational kinematics. This analysis showed that SLF nymphs are able to use posture changes and drag torques to control their angular velocity, and hence their orientation, thereby facilitating predominately successful landings when jumping. SummaryHigh-speed video revealed that juvenile spotted lanternflies are adept at landing after tumbling rapidly midair during jumping. We present computer simulations and realistic 3D models to help explain these abilities.

Fish turn extremely often, but this behavior is relatively understudied due to how challenging it can be to get fish to perform such an unsteady maneuver repeatedly. Specifically, little is known about whether fish control turns differently at different turning rates. Here we address the challenge of studying turning by developing a device that elicits turns repeatedly at specific speeds. Using this device, we compare the swimming kinematics of bluegill sunfish (Lepomis macrochirus) during fast and slow turns through 180 degrees. We find that the fish behave differently when turning quickly than when turning slowly: a fast turn is not a sped up slow turn, but is kinematically distinct. In particular, during fast turns, bluegill bend their bodies to minimize moment of inertia before they maximize torque, while in slow turns they maximize torque first, before they bend their bodies. In fast turns, they also beat their pectoral fins at a higher frequency, but take fewer pectoral fin strokes. Differences between the two speed turns may be due to initial momentum and how momentum is conserved throughout the turn, because fast turns have higher initial linear momentum that they can convert into angular momentum to turn around. Summary statementBluegill change how they handle torque and moment of inertia when turning rapidly than when turning slowly. Tradeoffs between linear and angular momentum may play a key role.

Trophallaxis is the mutual exchange and direct transfer of liquid food among eusocial insects such as ants, termites, wasps, and bees. This process allows efficient dissemination of nutrients and is crucial for the colonys survival. In this paper, we present a data-driven agent-based model and use it to explore how the interactions of individual bees, following simple, local rules, affect the global food distribution. We design the rules in our model using laboratory experiments on honeybees. We validate its results via comparisons with the movement patterns in real bees. Using this model, we demonstrate that the efficiency of food distribution is affected by the density of the individuals, as well as the rules that govern their behavior: e.g., how they move and whether or not they aggregate. Specifically, food is distributed more efficiently when donor bees do not always feed their immediate neighbors, but instead prioritize longer motions, sharing their food with more-distant bees. This non-local pattern of food exchange enhances the overall probability that all of the bees, regardless of their position in the colony, will be fed efficiently. We also find that short-range attraction improves the efficiency of the food distribution in the simulations. Importantly, this model makes testable predictions about the effects of different bee densities, which can be validated in experiments. These findings can potentially contribute to the design of local rules for resource sharing in swarm robotic systems.

The control and stability of flying and swimming animals is typically determined by measuring their responses to discrete gust perturbations. For the rigorous measurement and analysis of such responses, it is necessary to generate gusts that are precise, controllable and repeatable. Here, we present a method to generate discrete gusts under laboratory conditions using a vortex ring. Unlike other methods of gust generation, the vortex ring can be well characterized and is highly controllable. We first outline the theoretical basis for the design of a gust generator, and then describe an apparatus that we developed to generate discrete gusts. As a case study, we tested the efficacy of this method on freely-flying soldier flies Hermetia illucens. The method described here can be used to study diverse phenomena ranging from natural flight and swimming in insects, birds, bats and fishes, to the artificial flight of drones and micro-aerial vehicles.

Large commercial and military aircraft can operate in a wide range of turbulent conditions, except during extreme weather events such as cyclones. Smaller man-made vehicles, such as micro aerial vehicles (MAVs) and nano aerial vehicles (NAVs), are significantly more sensitive to routine environmental wind fluctuations, making them difficult to control. In contrast, insects exhibit remarkable stability in naturally gusty conditions. Despite this, few studies have systematically investigated the impact of gusts and turbulence on insect flight performance. To address this gap and to gain fundamental insights into insect flight stability under gusty conditions, we examined the flight of freely flying black soldier flies subjected to a discrete head-on aerodynamic gust in a controlled laboratory environment. Flight motions were recorded using two high-speed cameras, and body and wing kinematics were analyzed across 14 distinct cases. In response to the gust, we observed consistent features across the cases: (1) asymmetry in wing stroke amplitude, (2) large changes in body roll angle--up to 160{degrees}--occurring over approximately two wing beats ([~]20 ms) with recovery over [~]9 wing beats, (3) transient pitch-down attitude, and (4) deceleration in the flight direction. These rapid responses, combining passive and active control mechanisms, provide insight into the flight control strategies employed by insects. The findings offer valuable guidance for the design of MAVs and NAVs capable of robustly responding to gusts and unsteady airflow in natural environments.

Humans ability to grasp and dynamically manipulate objects with their hands is unmatched by current robots. To better understand human dynamic manipulation, we studied dice stacking, a task in which humans form a vertical stack of dice from a set of initially unstacked playing dice using an overturned cup and the surface of a table. This task is high dimensional and under-actuated, so it may superficially seem an incredible feat of state estimation and feedback control, but we show that this task is amenable to open-loop strategies. We simulated a cup with dice oscillated by fixed arm movement patterns using two different computer simulation frameworks with different contact models. These simulations showed that, for a range of arm and wrist movements, the dice naturally stack without any dice state feedback. We verified the predictions of these simulations with a physical robot. Thus, we have added dice stacking to the small list of dynamic manipulation tasks that can be robustly performed open-loop. We speculate that, for highly under-actuated tasks, humans may be biased to learn open-loop strategies over state feedback strategies. Future work could investigate the presence of such a bias in humans and its potential value for reinforcement learning algorithms.

Animals and living organisms are continuously adapting to changes in their environment. How do animals, especially those that are critical to their ecosystem, respond to rapidly changing conditions in their environment? Here, we report on the three-dimensional trajectories of flying honeybees under calm and windy conditions in front of the hive entrance. We also investigate the pitch and yaw in our experiments. We find that the mean velocities, accelerations and angular velocities of honeybees increase with increasing wind speeds. We observed that pair separation between honeybees is highly controlled and independent of wind speeds. Our results on the coordination used by honeybees may have potential applications for coordinated flight of unmanned aerial vehicles.

To better understand the turning flight characteristics of the bees, we developed a procedure for estimating the instantaneous total force generated by the bee, along with its centrifugal force component, at each instant of time. We calculated the magnitude and direction of the total force vector (TFV) with respect to the three body axes of the bee and examined its variation with time during turning flights. The results of this study revealed that turns in the cloud are executed by (a) holding the magnitude of the TFV vector constant and (b) by redirecting the body (and therefore the turning force) appropriately to execute a coordinated turn. We also calculated and analysed the TFVs of bees flying in a curved tunnel. The characteristics of these TFVs (magnitude and direction) are very similar to those for bees flying in the cloud. This is a novel finding as there are no studies which have estimated the instantaneous flight force magnitude and direction of a turning bee (these are not saccadic or evasive turns) in an outdoor or indoor setup. However, similar results have been reported for pigeons and cockatiels while executing smooth turns in the horizontal plane.

Body size is the major factor to the flight mechanics in animals. To fly at low Reynolds numbers, miniature insects have adaptations in kinematics and wing structure. Many microinsects have bristled wings, which reduce inertia and power requirements when providing good aerodynamic efficiency. But both bristled and membranous-winged microinsects fly at Reynolds numbers of about 10. Yet, the kinematics of the smallest known membranous-winged species have not been studied sufficiently. The available data are limited to the forewings of a relatively large parasitoid wasp Encarsia formosa. We studied kinematics of wings and body and flight performance in one of the smallest membranous-winged wasps, Trichogramma telengai (0.5 mm body length, Re = 12). T. telengai reaches 29 cm s-1 speed and 7 m s-2 acceleration in horizontal flight which are comparable with the flight performance of other microinsects. The wingbeat cycle is characterized by high frequency (283 Hz) and stroke amplitude (149{degrees}) and includes U-shaped strokes at high angles of attack and prolonged clap-and-fling. The hindwings move with a slight phase shift and smaller amplitude than the forewings. T. telengai differs from large membranous-winged insects and miniature featherwing beetles in kinematics, but it is fundamentally similar to E. formosa (Re = 18, membranous wings) and thrips Frankliniella occidentalis (Re = 15, bristled wings). We showed that, at Re {approx} 101, both membranous and bristled-winged insects have sufficient flight performance. Further study of the bristled-winged insects will make it possible to define the size limits of effectiveness of different wing structures.

Collisions between birds and airplanes, bird strikes, can damage aircrafts, resulting in delays and cancellation of flights, costing the international civil aviation industry more than 1.4 billion U.S. dollars annually. Bird deterrence is therefore crucial, but the effectiveness of all available deterrence methods is limited. For example, live avian predators can be a highly effective deterrent, because potential prey will not habituate to them, but live predators cannot be controlled with sufficient precision. Thus, there is an urgent need for new deterrence methods. To this end we developed the RobotFalcon, a device that we modelled after the peregrine falcon, a cosmopolitan predator that preys on a large range of bird species. Mimicking natural hunting behaviour, we tested the effectiveness of the RobotFalcon to deter flocks of corvids, gulls, starlings and lapwings. We compared its effectiveness with that of a drone, and of conventional methods routinely applied at a military airbase. We show that the RobotFalcon scared away bird flocks from fields immediately, and these fields subsequently remained free of bird flocks for hours. The RobotFalcon outperformed the drone and the best conventional method at the airbase (distress calls). Importantly, there was no evidence that bird flocks habituated to the RobotFalcon. We propose the RobotFalcon to be a practical and ethical solution to drive away bird flocks with all advantages of live predators but without their limitations. HighlightsO_LIWe present and test a new method of deterring of deterring birds, the RobotFalcon. C_LIO_LIThe RobotFalcon chased away flocks fast and prevented early returns. C_LIO_LIThe RobotFalcon outperformed both a drone and convential methods. C_LIO_LINo evidence of habituation to the RobotFalcon was found during the study period. C_LI

Centimeter-scale fliers that combine wings with springy elements must contend with the high power requirements and mechanical constraints of flapping wing flight. Insects utilize elastic energy exchange to reduce the inertial costs of flapping wing flight and potentially match wingbeat frequencies to a mechanical resonance. Flying at resonance may be energetically favorable under steady conditions, but it is difficult to modulate the frequency of a resonant system. Evidence suggests that insects utilize frequency modulation over long time scales to adjust aerodynamic forces, but it remains an open question the extent to which insects can modulate frequency on the wingstroke-to-wingstroke timescale. If wingbeat frequencies deviate from resonance, the musculature must work against the elastic flight system, thereby potentially increasing energetic costs. To assess how insects address the simultaneous needs for power and control, we tested the capacity for wingstroke-to-wingstroke wingbeat frequency modulation by perturbing free hovering Manduca sexta with vortex rings while recording high-speed video at 2000 fps. Because hawkmoth flight muscles are synchronous, there is at least the potential for the nervous system to modulate frequency on each wingstroke. We observed {+/-} 16% wingbeat frequency modulation in just a few wing strokes. Via instantaneous phase analysis of wing kinematics, we found that over 85% of perturbation responses required active changes in motor input frequency. Unlike their robotic counterparts that explicitly abdicate frequency modulation in favor of energy efficiency, we find that wingstroke-to-wingstroke frequency modulation is an underappreciated control strategies that complements other strategies for maneuverability and stability in insect flight.

Intermittent locomotion composed of periods of active flapping/stroking followed by inactive gliding has been observed with species that inhabit both aerial and marine environments. However, studies on the energetic benefits of a fluke-and-glide (FG) gait during horizontal locomotion are limited for dolphins. This work presents a physics-based model of FG gait and analysis of the associated costs of transport of bottlenose dolphins (Tursiops truncatus). New estimates of gliding drag coefficients for the model were estimated experimentally from free-swimming bottlenose dolphins. The data-driven approach used kinematic measurement from 84 hours of biologging tag data collected from 3 animals to estimate the coefficients. A set of 532 qualified gliding events were automatically extracted for gliding drag coefficient estimation, and an additional 783 FG bouts were parameterized and used to inform the model-based dynamic analysis. Experimental results indicate that FG gait was preferred at speeds around 2.2 - 2.7 m/s. Observed FG bouts had an average duty factor of 0.45 and gliding duration of 5 sec. The average associated metabolic cost of transport (COT) and mechanical cost of transport (MECOT) of FG gait are 2.53 and 0.35 J {middle dot} m-1 {middle dot} kg-1 at the preferred speeds. This corresponded to an 18.9% and 27.1% reduction in cost when compared to modeled continuous fluking gait at the same reference speed. Average thrust was positively correlated with fluking frequency and amplitude as animals accelerated during the FG bouts. While fluking frequency and amplitude were negatively correlated for a given thrust range. These results support the supposition that FG gait enhances the horizontal swimming efficiency of bottlenose dolphins and provides new dynamical insights into the gait of these animals.

We propose a novel system for long-term monitoring of Drosophila body mass. In this approach, a cantilever beam is placed inside a Drosophila culture vial and undergoes random vibrations induced by Drosophila landings. An infrared camera connected to a microcomputer records these vibrations. Image processing techniques then extract the beams vibration signals from the video recordings. Applying the Euler-Bernoulli beam theory, we calculate the Drosophila body mass. As a demonstration, we used this system to measure body mass variations in wild-type Drosophila over 14 days. Summary statementThis study presents a system that enables long-term monitoring of fruit fly body mass, offering new opportunities to study relationships between genes, circadian rhythms, phenotype, and long-term mass variation.

Muscles act through elastic and dissipative elements to mediate movement, but these elements can introduce dissipation and filtering which are important for energetics and control. The high power requirements of flapping flight can be reduced by the insects exoskeleton, which acts as a structurally damped spring under purely sinusoidal deformation. However, this purely sinusoidal dynamic regime does not encompass the asymmetric wing strokes of many insects or non-periodic deformations induced by external perturbations. As such, it remains unknown whether a structural damping model applies broadly and what implications it has for control. We used a vibration testing system to measure the mechanical properties of isolated Manduca sexta thoraces under symmetric, asymmetric, and band-limited white noise deformations. We measured a thoracic stiffness of 2980 Nm-1 at 25 Hz and physiological peak-to-peak amplitude of 0.92 mm. Power savings and dissipation were indistinguishable between symmetric and asymmetric conditions, demonstrating that no additional energy is required to deform the thorax non-sinusoidally. Under white noise conditions, stiffness and damping were invariant with frequency, which is consistent with a structural damping model and suggests the thorax has no frequency-dependent filtering properties. A simple flat frequency response function fits our measured frequency response. This work demonstrates the potential of structurally damped materials to simplify motor control by eliminating any velocity-dependent filtering that viscoelastic elements usually impose between muscle and appendage.

Insects are exceptionally robust walkers. Although different species exhibit distinct anatomical and functional specializations, they are also highly adaptive within these constraints. How such adaptations enable insects to efficiently navigate diverse environments and perform mechanical tasks remains far from fully explored. The mole cricket, which dwells underground, is one of the least studied insects, largely due to its cryptic lifestyle. It excels at digging tunnels and exhibits extreme morphological adaptations, particularly its exceptional fossorial forelegs. Its versatile locomotion, above and below ground, makes the mole cricket an attractive model system for studying the biomechanics of insect movement. Here we provide the first quantitative characterization of mole cricket locomotion. Using a tunnel-like arena, we recorded freely-moving insects and analyzed their various locomotion gaits. We identified and described three main modes of locomotion, including a backward-bound gait that has not previously been reported in any insect. To test specific hypotheses regarding form-function relationships and the generation of thrust, we integrated biomechanical modeling and deep reinforcement learning to simulate the observed gaits. Our work opens several future directions, from exploring context-dependent gait transitions to bio-inspired technological innovations.

Bloodworms, Glycera dibranchiata, possess an eversible proboscis that normally remains concealed within their bodies but explosively everts if the worm attacks or burrows. How does the bloodworm evert quickly and reliably? In a series of experiments, we characterize bloodworm kinematics, pressure, and material properties to estimate the criteria for eversion safely without rupture of the proboscis. We predict the proboscis can withstand pressures 50 times higher and bending strains up to three times higher than the respective values observed. We also present a dimensional analysis of eversion, finding that everting animals, from frogs to snails to sharks, do not satisfy Froudes law for equivalence of velocities. Our findings may help inspire the development of pressure-driven soft robots with efficient retraction capabilities.

The study of animal locomotion and neuromechanical control offers valuable insights for advancing research in neuroscience, biomechanics, and robotics. We have developed FARMS (Framework for Animal and Robot Modeling and Simulation), an open-source, interdisciplinary framework, designed to facilitate access to modeling, simulation, and analysis of animal locomotion and bio-inspired robotic systems. By providing an accessible and user-friendly platform, FARMS aims to lower the barriers for researchers to explore the complex interactions between the nervous system, musculoskeletal structures, and their environment. Integrating the MuJoCo physics engine in a modular manner, FARMS enables realistic simulations and fosters collaboration among neuroscientists, biologists, and roboticists. FARMS has already been extensively used to study locomotion in animals such as mice, drosophila, fish, salamanders, and centipedes, serving as a platform to investigate the role of central pattern generators and sensory feedback. This article provides an overview of the FARMS framework, discusses its interdisciplinary approach, showcases its versatility through specific case studies, and highlights its effectiveness in advancing our understanding of locomotion. Overall, the goal of FARMS is to contribute to a deeper understanding of animal locomotion, the development of innovative bio-inspired robotic systems, and promote accessibility in neuromechanical research.