Robot swings into treetops

It abseils down from a height and swings around obstacles: Robot Avocado will one day maneuver through the canopy of the rainforest and collect data for researchers about this difficult-to-access habitat.

It’s called an avocado and looks a bit like one too: The innovative robot, which researchers are currently developing with the support of the Swiss National Science Foundation, has a robust housing that resembles the shape of the green fruit. Hidden inside is a technology that enables the robot to navigate autonomously through treetops. Avocado is one of the latest inventions in environmental robotics. "The idea behind this field is to get robots out of the factory halls and use them outdoors for environmental research," explains Steffen Kirchgeorg, a doctoral student at ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research in Birmensdorf.

Especially in tropical rainforests - the areas with the highest biodiversity worldwide - a large part of life takes place in the dense canopy. Exploring these habitats is extremely difficult: research teams climbing trees can only collect data selectively. The environment is also a challenge for existing robots: flying drones are not suitable because their rotors would get tangled up in the leaves. Climbing robots have difficulties with the different thicknesses and textures of branches.

Like a spider on a thread

"That’s why we came up with the idea of trying to access the tree from above," explains Kirchgeorg. The robot is attached to a high branch of the tree with a rope and lowered from there into its crown. The researchers borrowed the idea from spiders, which also abseil down threads. In the current test phase, the researchers are still attaching the robot manually by climbing up the tree. Later, a drone could also serve as a kind of mother ship that transports the robot to inaccessible regions and anchors it in the uppermost branches of the trees.

Once docked, Avocado can move up and down independently - thanks to a cable winch hidden in the upper section of the housing. In the bulbous part, where the pit of the real exotic fruit is located, the robot has two rotors. With their help, it gains momentum and can maneuver around branches, leaves and other obstacles.

Together with colleagues from Stefano Mintchev’s research group, Kirchgeorg has tested in simulations how the robot can make its own way through the skillful use of winches and rotors. It receives information about its environment from a built-in camera. The whole thing is not that easy, as Kirchgeorg explains: "The treetops have very difficult lighting conditions with lots of changes between light and dark. We are now trying to use the camera to achieve depth perception even under these conditions." After all, the robot can already master a predefined indoor course and has also survived a test mission in a real tree.

Where no one else can go

Once Avocado has fully mastered autonomous locomotion, Kirchgeorg can imagine its long-term use in the rainforest: Because by being attached to the rope, the robot only uses battery power when it has to move - at best, a solar cell from above could also conduct electricity down through the rope. The robot is also so quiet that it does not disturb the creatures living in the tree.

Attachment to the rope has another advantage: the robot can carry quite a lot of weight and can therefore be equipped with a lot of technology - for example with humidity and temperature sensors to map the microclimate in different sections of the tree canopy. Or with gripper arms and air filters to collect DNA samples. "We may even find new animal or plant species in the process," says Kirchgeorg. After all, there are most likely a large number of previously undiscovered species hiding in the rainforest canopy.

With Avocado and other research activities, the team, together with other ETH research groups, has made it to the finals of the highly endowed XPRIZE Rainforest competition. This foundation honors innovations that accelerate the monitoring of biodiversity in tropical rainforests. Because time is of the essence: More and more rainforests - and with them valuable habitats - are disappearing due to agricultural use and deforestation.

(*) S. Kirchgeorg et al.: Design, Modeling and Control of AVOCADO: A Multimodal Aerial-Tethered Robot for Tree Canopy Exploration. IEEE Transactions on Robotics (2023)