Soft landing: Drone collects DNA samples from thin, wobbly tree branches

(This article is also available in English)

Climate change and the spread of humans into historically species-rich habitats have led to a sometimes dramatic decline in global biodiversity. However, it is difficult to quantify the extent of this decline. For several years, the analysis of so-called environmental DNA (eDNA) has been established. This is DNA that is released into the environment in small amounts. Species living there can be cataloged from the sequencing of such samples. However, while eDNA from the sea can be obtained relatively easily through water sampling, sourcing eDNA on land is more difficult.

Emanuele Aucone from ETH Zurich and colleagues have now developed a drone that can land semi-autonomously on tree branches to collect DNA samples. To do this, it is first steered over the branch by remote control and then starts to land autonomously. An adhesive film captures the surrounding eDNA. In an outdoor test sampling seven trees in the Swiss lowlands, the drone actually made it possible to identify different species.

Drone floats more than it lands

However, “landing” only roughly describes the action of the drone – it’s more of a careful nudge that the drone performs. The researchers wanted the quadcopter to be able to land on very thin branches. How stable such a branch is cannot be seen exactly when approaching. So, the autonomous landing mechanism had to work regardless of the rigidity of the branch. The researchers solved this with a kind of cage that surrounds the drone.

A horizontal and a vertical hoop are point-connected to a force sensor in the middle. Software measures the forces that occur when landing from different directions and, by adjusting the rotors, tries to set a predetermined force at the point of contact with the branch without the machine starting to slide or tilt. Since the contact force is very small, the machine hovers over the branch rather than landing directly on it.

However, the Swiss researchers are not the first to have built a drone that can land more or less elegantly on branches or poles. Because this ability makes it possible, for example, to fly drones to a target and park them to save energy, so to speak. In 2019, researchers from Stanford University presented mechanical grippers that function similarly to the feet of birds of prey and close extremely quickly around a branch on contact. A balance algorithm then ensures that the drone remains stable.

(wst)