Aerial robot piloted in steep relief by optic flow sensors

We have developed a new vision based autopilot able to make a micro-air vehicle automatically navigate in steep relief. It uses onboard Optic Flow sensors inspired by the housefly´s Elementary Motion Detectors (EMDs) that were previously investigated at our Laboratory with electrophysiological and micro-optical techniques. The paper investigates how the ground avoidance performances of the former OCTAVE robot could be enhanced to cope with steep relief. The idea is to combine frontal and ventral OF sensors and to merge feedback and feedforward loops. In the new robot, called OCTAVE(2), a feedback loop adjusts the lift so as to keep the ventral OF constant, while a feedforward loop based on a forward looking EMD sensor serves to anticipate the steep relief. We test the new autopilot on a 100-gram tethered rotorcraft that circles indoors over an environment composed of contrasting features randomly arranged on the floor. We show that OCTAVE(2) succeeds in following a relatively steep relief (maximum slope 17deg) while navigating close to the ground (groundheight in the order of lm). This risky task is performed thanks to a minimalist electronic visual system: the OF sensor suite is lightweight (4.3-grams including the lenses), and is therefore mounted onboard.