Pranav Khandelwal

This review highlights the largely understudied behavior of gliding locomotion, which is exhibited by a diverse range of animals spanning vertebrates and invertebrates, in air and in water. The insights in the literature gained from January 2022 to December 2022 continue to challenge the previously held notion of gliding as a relatively simple form of locomotion. Using advances in field/lab data collection and computation, the highlighted studies cover gliding in animals including seabirds… Show more

This review highlights the largely understudied behavior of gliding locomotion, which is exhibited by a diverse range of animals spanning vertebrates and invertebrates, in air and in water. The insights in the literature gained from January 2022 to December 2022 continue to challenge the previously held notion of gliding as a relatively simple form of locomotion. Using advances in field/lab data collection and computation, the highlighted studies cover gliding in animals including seabirds, flying lizards, flying snakes, geckos, dragonflies, damselflies, and dolphins. Altogether, these studies present gliding as a sophisticated behavior resulting from the interdependent aspects of morphology, sensing, environment, and likely selective pressures. This review uses these insights as inspiration to encourage researchers to revisit gliding locomotion, both in the animal's natural habitat and in the laboratory, and to investigate questions spanning gliding biomechanics, ecology, sensing, and the evolution of animal flight. Show less

Landing on vertical surfaces in challenging environments is a critical ability for multimodal robots—it allows the robot to hold position above the ground without expending energy to hover. Asian flat-tailed geckos (Hemidactylus platyurus) are observed to glide and perch on vertical surfaces by relying on their tail and body morphology, potentially reducing the control effort to perch. This novel perching mechanism using a bioinspired physical model is discussed and its tail and body parameters… Show more

Landing on vertical surfaces in challenging environments is a critical ability for multimodal robots—it allows the robot to hold position above the ground without expending energy to hover. Asian flat-tailed geckos (Hemidactylus platyurus) are observed to glide and perch on vertical surfaces by relying on their tail and body morphology, potentially reducing the control effort to perch. This novel perching mechanism using a bioinspired physical model is discussed and its tail and body parameters to determine their influence on perching success and the kinematics of the gecko's dynamic landing maneuver are adjusted. Perching performance is evaluated by changing the model's torso and tail stiffness. Combining a compliant torso and stiff tail enables the model to passively perch on a vertical substrate with a success rate >90%, compared with ≈10% without a tail attached. A compliant torso is necessary to absorb the in-flight kinetic energy and accommodate the uncertainties in approach conditions. Similar to the gecko's perching strategy, the stiff tail pushes against the substrate, preventing the model from falling backward head over heels. These findings highlight the critical role of tail and material stiffness for perching and provide a simplified mechanism to impart perching capabilities in robots. Show less

Gliding animals change their body shape and posture while producing and modulating aerodynamic forces during flight. However, the combined effect of these different factors on aerodynamic force production, and ultimately the animal’s gliding ability, remains uncertain. Here, we quantified the time-varying morphology and aerodynamics of complete, voluntary glides performed by a population of wild gliding lizards (Draco dussumieri) in a seven-camera motion capture arena constructed in their… Show more

Gliding animals change their body shape and posture while producing and modulating aerodynamic forces during flight. However, the combined effect of these different factors on aerodynamic force production, and ultimately the animal’s gliding ability, remains uncertain. Here, we quantified the time-varying morphology and aerodynamics of complete, voluntary glides performed by a population of wild gliding lizards (Draco dussumieri) in a seven-camera motion capture arena constructed in their natural environment. Our findings, in conjunction with previous airfoil models, highlight how three-dimensional (3D) wing shape including camber, planform, and aspect ratio enables gliding flight and effective aerodynamic performance by the lizard up to and over an angle of attack (AoA) of 55° without catastrophic loss of lift. Furthermore, the lizards maintained a near maximal lift-to-drag ratio throughout their mid-glide by changing body pitch to control AoA, while simultaneously modulating airfoil camber to alter the magnitude of aerodynamic forces. This strategy allows an optimal aerodynamic configuration for horizontal transport while ensuring adaptability to real-world flight conditions and behavioral requirements. Overall, we empirically show that the aerodynamics of biological airfoils coupled with the animal’s ability to control posture and their 3D wing shape enable efficient gliding and adaptive flight control in the natural habitat. Show less

Gliding animals traverse cluttered aerial environments when performing ecologically relevant behaviours. However, it is unknown how gliders execute collision-free flight over varying distances to reach their intended target. We quantified complete glide trajectories amid obstacles in a naturally behaving population of gliding lizards inhabiting a rainforest reserve. In this cluttered habitat, the lizards used glide paths with fewer obstacles than alternatives of similar distance. Their takeoff… Show more

Gliding animals traverse cluttered aerial environments when performing ecologically relevant behaviours. However, it is unknown how gliders execute collision-free flight over varying distances to reach their intended target. We quantified complete glide trajectories amid obstacles in a naturally behaving population of gliding lizards inhabiting a rainforest reserve. In this cluttered habitat, the lizards used glide paths with fewer obstacles than alternatives of similar distance. Their takeoff direction oriented them away from obstacles in their path and they subsequently made mid-air turns with accelerations of up to 0.5 g to reorient towards the target tree. These manoeuvres agreed well with a vision-based steering model which maximized their bearing angle with the obstacle while minimizing it with the target tree. Nonetheless, negotiating obstacles reduced mid-glide shallowing rates, implying greater loss of altitude. Finally, the lizards initiated a pitch-up landing manoeuvre consistent with a visual trigger model, suggesting that the landing decision was based on the optical size and speed of the target. They subsequently followed a controlled-collision approach towards the target, ending with variable impact speeds. Overall, the visually guided path planning strategy that enabled collision-free gliding required continuous changes in the gliding kinematics such that the lizards never attained theoretically ideal steady-state glide dynamics. Show less

Gliding animals undertake a series of complex aerodynamic and morphological adjustments in order to execute a transition from perching or resting to gliding. Take-off requires the animal to generate adequate thrust, deploy its wing and correct its body orientation immediately after launching itself towards the landing target. In order to accomplish this, the animal uses a combination of limb and tail movements along with dynamic wing and body morphing. We used two cameras recording at 240 Hz to… Show more

Gliding animals undertake a series of complex aerodynamic and morphological adjustments in order to execute a transition from perching or resting to gliding. Take-off requires the animal to generate adequate thrust, deploy its wing and correct its body orientation immediately after launching itself towards the landing target. In order to accomplish this, the animal uses a combination of limb and tail movements along with dynamic wing and body morphing. We used two cameras recording at 240 Hz to film take-offs in a wild population of flying lizards, Draco dussumieri, from vertical tree surfaces for a glide distance of 5.5 m. We tracked body points including the head, limbs, wings, posterior end and tail in 3D to study take-off biomechanics in the field. Take-off was initiated by the lizard rotating from a vertical to horizontal position on the tree trunk and using its hind limbs to thrust itself in the direction of the landing tree accelerating at ~9 ms-2 and reaching a velocity of ~2.5 ms-1 by the time of complete wing deployment. Dracos are unique among gliding animals in possessing a head-mounted canard along with a main wing membrane which is supported by ribs on either side. Deployment of the canard and main wing began immediately after launch with canards being fully extended first at ~0.05 s followed by wing in ~0.10 s. The main wing was extended and held in position independently of the limbs during take-off. The forelimbs were extended from the body and eventually held parallel to the leading edge of the wing with the wrists resting on its top surface, potentially forming a leading edge slot. We observed pronounced tail movement during the take-off phase along with changes in body roll, pitch and yaw suggesting a role in controlling body orientation. These observations provide a first detailed look at Draco take-off in a natural setting. Show less

Conducting polymers have the combined advantages of metal conductivity with ease in processing and biocompatibility; making them extremely versatile for biosensor and tissue engineering applications. However, the inherent brittle property of conducting polymers limits their direct use in such applications which generally warrant soft and flexible material responses. Addition of fillers increases the material compliance, but is achieved at the cost of reduced electrical conductivity. To retain… Show more

Conducting polymers have the combined advantages of metal conductivity with ease in processing and biocompatibility; making them extremely versatile for biosensor and tissue engineering applications. However, the inherent brittle property of conducting polymers limits their direct use in such applications which generally warrant soft and flexible material responses. Addition of fillers increases the material compliance, but is achieved at the cost of reduced electrical conductivity. To retain suitable conductivity without compromising the mechanical properties, we fabricate an electroactive blend (dPEDOT) using low grade PEDOT:PSS as the base conducting polymer with polyvinyl alcohol as filler and glycerol as a dopant. Bulk dPEDOT films show a thermally stable response till 110 °C with over seven fold increase in room temperature conductivity as compared to 0.002 S cm−1 for pristine PEDOT:PSS. We characterize the nonlinear stress–strain response of dPEDOT, well described using a Mooney–Rivlin hyperelastic model, and report elastomer-like moduli with ductility ∼ fives times its original length. Dynamic mechanical analysis shows constant storage moduli over a large range of frequencies with corresponding linear increase in tan(δ). We relate the enhanced performance of dPEDOT with the underlying structural constituents using FTIR and AFM microscopy. These data demonstrate specific interactions between individual components of dPEDOT, and their effect on surface topography and material properties. Finally, we show biocompatibility of dPEDOT using fibroblasts that have comparable cell morphologies and viability as the control, which make dPEDOT attractive as a biomaterial. Show less