Nothing Can Keep This Drone Down

When life knocks you down, you've got to get back up. Ladybugs take this advice seriously in the most literal sense. If caught on their backs, the insects are able to use their tough exterior wings, called elytra (of late made famous in the game Minecraft), to self-right themselves in just a fraction of a second.

Inspired by this approach, researchers have created self-righting drones with artificial elytra. Simulations and experiments show that the artificial elytra can not only help salvage fixed-wing drones from compromising positions, but also improve the aerodynamics of the vehicles during flight. The results are described in a study published July 9 in IEEE Robotics and Automation Letters.

Charalampos Vourtsis is a doctoral assistant at the Laboratory of Intelligent Systems, Ecole Polytechnique Federale de Lausanne in Switzerland who co-created the new design. He notes that beetles, including ladybugs, have existed for tens of millions of years. Over that time, they have developed several survival mechanisms that we found to be a source of inspiration for applications in modern robotics," he says.

His team was particularly intrigued by beetles' elytra, which for ladybugs are their famous black-spotted, red exterior wing. Underneath the elytra is the hind wing, the semi-transparent appendage that's actually used for flight.

When stuck on their backs, ladybugs use their elytra to stabilize themselves, and then thrust their legs or hind wings in order to pitch over and self-right. Vourtsis' team designed Micro Aerial Vehicles (MAVs) that use a similar technique, but with actuators to provide the self-righting force. Similar to the insect, the artificial elytra feature degrees of freedom that allow them to reorient the vehicle if it flips over or lands upside down," explains Vourtsis.

The researchers created and tested artificial elytra of different lengths (11, 14 and 17 centimeters) and torques to determine the most effective combination for self-righting a fixed-wing drone. While torque had little impact on performance, the length of elytra was found to be influential.

On a flat, hard surface, the shorter elytra lengths yielded mixed results. However, the longer length was associated with a perfect success rate. The longer elytra were then tested on different inclines of 10, 20 and 30, and at different orientations. The drones used the elytra to self-right themselves in all scenarios, except for one position at the steepest incline.

The design was also tested on seven different terrains: pavement, course sand, fine sand, rocks, shells, wood chips and grass. The drones were able to self-right with a perfect success rate across all terrains, with the exception of grass and fine sand. Vourtsis notes that the current design was made from widely available materials and a simple scale model of the beetle's elytra-but further optimization may help the drones self-right on these more difficult terrains.

As an added bonus, the elytra were found to add non-negligible lift during flight, which offsets their weight.

Vourtsis says his team hopes to benefit from other design features of the beetles' elytra. We are currently investigating elytra for protecting folding wings when the drone moves on the ground among bushes, stones, and other obstacles, just like beetles do," explains Vourtsis. That would enable drones to fly long distances with large, unfolded wings, and safely land and locomote in a compact format in narrow spaces."