A new system for aerial robots ensures flight stability using optic flow sensors instead of an accelerometer. Inspired by the way insects see the world, the sensors allow the robot to autonomously avoid obstacles while flying through a tunnel with uneven walls, without measuring speed or altitude.
Normally, aircraft use an inertial measurement unit which includes accelerometers to the stabilize its roll and pitch with respect to the direction of the center of the Earth. (The accelerometer measures all the accelerations of the aircraft including gravity, which is always directed toward the center of the Earth.) Insects, however, fly without an equivalent tool.
Researchers Fabien Expert and Franck Ruffier of the Institut des Sciences du Mouvement — Etienne-Jules Marey decided to use this interesting insect ability as the basis for a tethered flying robot that worked without measuring speed or altitude. 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: 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. The research team calls their robot the BeeRotor.
To measure optic flow, BeeRotor is equipped with a mere 24 photodiodes (or pixels) on 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.
BeeRotor has three feedback loops, which act as three reflexes that respond to the optic flow. The first feedback loop makes the robot change altitude, so it follows the floor or the roof. The second controls the robot’s speed, so that it doesn’t fly too fast for conditions. The third loop stabilizes 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.