Crash landing robots are inspired by geckos

Insights from tree-climbing geckos’ hard landings lead to better, more controlled landings in robotic aerial vehicles.

Agile flying robots are already playing an important role in various sectors and applications, including data collection, search and rescue, crop monitoring and forest fire management. However, even state-of-the-art drones have limited ability to land on uncertain terrain and difficult perches, such as the side of a building, tree, or pole.

“Landing quickly on vertical surfaces is one of the biggest challenges in aerial robotics,” explained Ardian Jusufi, leader of the Max Planck Group at the MPI for Intelligent Systems and the Swiss Federal Laboratories for Materials Science Technology. “Emulating this maneuver would expand its application space, such as in a post-earthquake debris field, or to assist firefighters, among other search and rescue scenarios.”

Today’s robots rely on rotors or ailerons to brake and reorient before landing, Jusufi says. “Landing on a wall requires integrating multiple sensor streams to control aerodynamic forces to bring the robot to the desired climbing body orientation for a dedicated landing maneuver,” he explained. “The process of integrating multiple sensor streams is computationally expensive, leading to slow reaction times to environmental perturbations.”

It was during a hike in the rainforests of Singapore that Jusufi encountered the Asian flat-tailed gecko, known not only for its unparalleled climbing abilities, but for its ability to slide between trees and land on surfaces vertical

“I was surprised to observe that these lizards hit the tree trunk headfirst and fall backwards, head over heels at extreme angles from the vertical surface, to land,” Jusufi said. “they collide with the tree at an astonishing speed of 22 km/h”.

These lizards rely on their torso and tail to dissipate the kinetic energy built up during their glide, sticking their landing by pressing their tail against the log and preventing them from falling head over heels. “I saw the potential of this mechanism to create multimodal robots capable of putting themselves in similar environments,” Jusufi said.

In a recent study published in Advanced intelligent systemsSo Jusufi and his group developed a prototype soft body based on the gecko’s size, shape and weight, and which uses what he called a “fall arrest response.” As with the gecko, the robot’s tail was critical to allow a safe landing, along with the rigidity of the torso.

“A compliant torso allows the robot to dissipate significant amounts of kinetic energy upon impact,” explained Chellapurath, lead author of this study. “After impact, the folded torso allows the robot’s hind limbs to engage the surface, and the stiff tail reduces bounce.”

As the tail is pressed against the wall, it provides counter-torque and prevents the robot from turning its head for the first time and dropping its head. “In this spirit, morphing structures and adaptive stiffness increasingly enable unprecedented robotic ambulation with simplified control provided by biomimetic materials and system-to-system relationships,” Jusufi said.

The tail is pressed against the wall providing counter torque and preventing the robot from turning head first. Illustrations by Melanie Eckermann

Surprisingly, for the crash landing to work properly, the team determined a full-length tail was needed: a half-tail wouldn’t do. “This is particularly interesting because it supports the idea that these lizards have potentially evolved to have tails of the appropriate length for their body locomotion capacity,” said Pranav Khandelwal, one of the authors of the study.

The scientists also tested different approach angles and impact speeds to account for different approach trajectories in order to simulate real-world scenarios. The “fall arrest response” performed well even when the approach angle and speed changed, demonstrating the versatility of this biologically inspired landing mechanism.

“The fall arrest response of geckos landing on a wall highlights the importance of compliance of tail and hind structures to ensure robustness in the face of uncertainty in unstructured natural terrain,” commented Robert Wood, professor at Harvard University who was not involved in the study. “And more broadly, the work of Jusufi and his lab highlights the utility of using bio-inspired robots to explore questions of biology in unprecedented ways.”

This study provides new insights into the requirements for hard landings and how they can be used to increase stability and simplify controlled landings in air vehicles.

The Max Planck group believes there is potential to expand the lander’s robustness by further tuning the robot’s material properties and testing it on a variety of challenging surfaces in different environments to push the robot’s capabilities.

Reference: Ardian Jusufi, et al., Morphologically Adaptive Crash Landing on a Wall: Soft-Bodied Models of Gliding Geckos with Varying Material Stiffnesses, Advanced Intelligent Systems (2022). DOI: 10.1002/aisy.202200120

Main image credit: Ardian Jusufi Lab

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