Visual guidance of honeybees approaching a vertical landing surface

Bioinspired adaptive visual servoing control for quadrotors

Since every flight ends in a landing and every landing is a potential crash, deceleration during landing is one of the most critical flying maneuvers. Here we implement a recently-discovered insect visual-guided landing strategy in which the divergence of optical flow is regulated in a step-wise fashion onboard a quadrotor for the task of visual servoing. This approach was shown to be a powerful tool for understanding challenges encountered by visually-guided flying systems. We found that landing on a relatively small target requires mitigation of the noise with adaptive low-pass filtering, while compensation for the delays introduced by this filter requires open-loop forward accelerations to switch from divergence setpoint. Both implemented solutions are consistent with insect physiological properties. Our study evaluates the challenges of visual-based navigation for flying insects. It highlights the benefits and feasibility of the switching divergence strategy that allows for faster and safer landings in the context of robotics.

Sticking the landing: Insect-inspired strategies for safely landing flapping-wing aerial microrobots

For flying insects, the transition from flight to surface locomotion requires effective touchdown maneuvers that allow stable landings on a variety of surfaces. Landing behaviors of insects are diverse, with some using more controlled flight approaches to landing, whereas others dampen collision impacts with parts of their bodies. The landing approaches of real insects inspired our current work, where we present a combined mechanical and control approach to achieving safe and accurate landings for flapping-wing microaerial vehicles. For the mechanical approach to landing, we took inspiration from the legs of the crane fly, designing lossy compliant legs that maximize energy dissipation during surface collisions. We explored three features in the compliant leg design: leg stance, number of joints, and joint placement. For the control approach to landing, the challenge lies in overcoming the aerodynamic ground effect near the surface. Leveraging the compliant leg design during impact, we designed the preimpact behavior, drawing inspiration from insect landing trajectories, to increase landing success. The proposed controlled landing sequence includes an initial acceleration from hovering, followed by deceleration toward the target, ending with a nonzero impact velocity, similar to what is observed in insects. Last, using an insect-scale flapping-wing aerial microrobot platform (Harvard RoboBee), we verified the controlled, safe, and accurate landing on natural terrain.

Follow the flower: approach-flight behaviour of bumblebees landing on a moving target

While landing on flowers, pollinating insects often have to deal with flower movement caused by wind. Here, we determined the landing performance of bumblebees on a moving artificial flower and how bees use their visual-motor system to control their landings. To do this, we built an experimental setup containing a physical model of a flower, moving sideways using sinusoidal kinematics at various oscillation frequencies (up to 0.65 Hz, at constant amplitude of 5 cm). We filmed the landings of Bombus terrestris bumblebees on this moving flower model and extracted the flight kinematics and trajectories using deep neural network-based videography tracking. The bumblebees were capable of compensating for the detrimental effects of flower movement on landing performance for flower movement frequencies up to 0.53 Hz. Only at our maximum frequency of 0.65 Hz did the percentage of successful landings decrease but landing accuracy and duration were not affected. To successfully land on the moving flower, the bumblebees gradually slowed down, aimed towards the middle of the flower and aligned with its movement. Our results indicated that bumblebees use modular visual-motor control feedback to do this: (1) they slow down by maintaining an approximately constant average optic expansion of the approaching flower image; (2) they aim towards the flower by keeping the flower in the middle of their view; (3) they align to the flower movement by minimizing the sideways optic flow of the moving flower image. Our findings increase our understanding of how flying insects land on flowers moved by wind.

Biomechanics and ontogeny of gliding in wingless stick insect nymphs (Extatosoma tiaratum)

Many wingless arboreal arthropods can glide back to tree trunks following free falls. However, little is known about the behaviors and aerodynamics underlying such aerial performance, and how this may be influenced by body size. Here, we studied gliding performance by nymphs of the stick insect Extatosoma tiaratum, focusing on the dynamics of J-shaped trajectories and how gliding capability changes during ontogeny. After being dropped 40 cm horizontally from a visual target, the first-instar nymphs landed on the target within 1.1 s. After reaching terminal speed (at ∼0.25 s), they initiated gliding with significant horizontal force, during which the overall lift-to-drag ratio increased from 0.16 to 0.48. This transition from parachuting to gliding is characterized by a damped oscillation in body pitch, initiated with a rapid nose-down pitching, and led to a higher-lift configuration with reduced body angle of attack. Among instars, increasing wing loading during ontogeny led to greater terminal speed, reduced agility during glide initiation and increased glide angle. Our study demonstrates that a sequence of controlled behaviors, from pre-glide descent to glide initiation and forward gliding, underlies their gliding aerodynamics, which in aggregate form the basis for J-shaped aerial trajectories. Selection for improved gliding performance in wingless arthropods may foster the evolution of more rapid maneuvers and of dedicated morphological traits (such as winglets) that contribute to an overall reduction in wing loading, either across ontogeny or during the evolution of larger body size.

A bio-inspired looming detection for stable landing in unmanned aerial vehicles. BIOINSPIRATION & BIOMIMETICS 2024;20:016007. [PMID: 39481235 DOI: 10.1088/1748-3190/ad8d99] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Flying insects, such as flies and bees, have evolved the capability to rely solely on visual cues for smooth and secure landings on various surfaces. In the process of carrying out tasks, micro unmanned aerial vehicles (UAVs) may encounter various emergencies, and it is necessary to land safely in complex and unpredictable ground environments, especially when altitude information is not accurately obtained, which undoubtedly poses a significant challenge. Our study draws on the remarkable response mechanism of the Lobula Giant Movement Detector to looming scenarios to develop a novel UAV landing strategy. The proposed strategy does not require distance estimation, making it particularly suitable for payload-constrained micro aerial vehicles. Through a series of experiments, this strategy has proven to effectively achieve stable and high-performance landings in unknown and complex environments using only a monocular camera. Furthermore, a novel mechanism to trigger the final landing phase has been introduced, further ensuring the safe and stable touchdown of the drone.

Bumblebees compensate for the adverse effects of sidewind during visually guided landings

Flying animals often encounter winds during visually guided landings. However, how winds affect their flight control strategy during landing is unknown. Here, we investigated how sidewind affects the landing performance and sensorimotor control of foraging bumblebees (Bombus terrestris). We trained bumblebees to forage in a wind tunnel, and used high-speed stereoscopic videography to record 19,421 landing maneuvers in six sidewind speeds (0 to 3.4 m s-1), which correspond to winds encountered in nature. Bumblebees landed less often in higher windspeeds, but the landing durations from free flight were not increased by wind. By testing how bumblebees adjusted their landing control to compensate for adverse effects of sidewind on landing, we showed that the landing strategy in sidewind resembled that in still air, but with important adaptations. Bumblebees landing in a sidewind tended to drift downwind, which they controlled for by performing more hover maneuvers. Surprisingly, the increased hover prevalence did not increase the duration of free-flight landing maneuvers, as these bumblebees flew faster towards the landing platform outside the hover phases. Hence, by alternating these two flight modes along their flight path, free-flying bumblebees negated the adverse effects of high windspeeds on landing duration. Using control theory, we hypothesize that bumblebees achieve this by integrating a combination of direct aerodynamic feedback and a wind-mediated mechanosensory feedback control, with their vision-based sensorimotor control loop. The revealed landing strategy may be commonly used by insects landing in windy conditions, and may inspire the development of landing control strategies onboard autonomously flying robots.