Researchers have developed the first aerial robot that is able to fly over uneven terrain using visual input to stabilise without an accelerometer.
Called BeeRotor, it adjusts its speed and avoids obstacles thanks to optic flow sensors inspired by insect vision.
It can fly along a tunnel with uneven, moving walls without measuring either speed or altitude.
All aircraft are currently equipped with an inertial measurement unit, including accelerometers.
This allows these aircraft to stabilise their roll and pitch with respect to the horizon or rather with respect to its perpendicular: the direction of the centre of the Earth.
An accelerometer measures all the accelerations of the aircraft including gravity, which is always directed towards the centre of the Earth.
However, this essential tool has no equivalent in insects, which fly quite happily without this information.
Researchers at the Institut des Sciences du Mouvement - Etienne-Jules Marey took inspiration from winged insects to create BeeRotor, a tethered flying robot able for the first time to adjust its speed and follow terrain with no accelerometer and without measuring speed or altitude.
With a weight of 80 grams and a length of 47 centimetres, it can, all by itself, avoid vertical obstacles in a tunnel with moving walls.
To achieve this, the researchers mimicked the ability of insects to use the passing landscape as they fly.
This is known as optic flow, the principle of which can readily be observed when driving along a motorway: the view in front is fairly stable, but looking out to either side, the landscape passes by faster and faster, reaching a maximum at an angle of 90 degrees to the path of the vehicle.
To measure optic flow, BeeRotor is equipped with a mere 24 photodiodes (or pixels) distributed at the top and the bottom of its eye.
This enables it to detect contrasts in the environment as well as their motion. As in insects, the speed at which a feature in the scenery moves from one pixel to another provides the angular velocity of the flow.
When the flow increases, this means that the robot's speed is also increasing or that the distance relative to obstacles is decreasing.
By way of a brain, BeeRotor has three feedback loops, which act as three different reflexes that directly make use of the optic flow.
The first feedback loop makes it change its altitude so as to follow the floor or the roof. The second one controls the robot's speed in order to adapt it to the size of the tunnel through which it flies.
The third loop stabilises the eye in relation to the local slope, using a dedicated motor. This enables the robot to always obtain the best possible field of view, independently of its degree of pitch.
The research was published in the journal Bioinspiration and Biomimetics.
