Combining sound and optic fow cues to reach a sound source despite lateral obstacles

In our project on the autonomous guidance of micro-air vehicles (MAVs) in confined indoor and outdoor environments, we have combined an insect vision-based autopilot with a directional sound sensor, with which a miniature hovercraft reaches a sound source along a corridor by automatically controlling its speed, its clearance from the walls and its body yaw. A hovercraft is an air vehicle endowed with natural roll and pitch stabilization characteristics, in which planar flight control systems can be developed conveniently. Our hovercraft is fully actuated by two rear and two lateral thrusters. It travels at a constant altitude (about 2 mm) and senses the obstacles by means of two lateral eyes that measure the right and left optic flows (OFs). The visuo-motor control system which has been previously called LORA III (lateral optic flow regulation autopilot, Mark III), is an insect-inspired dual of regulator consisting of two interdependent feedback loops, each of which has its own OF set-point and controls its own translational degree of freedom (surge or sway). The sound based control system servoes the robot course direction to the sound source direction estimated by an insect-inspired sound sensor. Our computer-simulated experiments show that the hovercraft can navigate along a tapered corridor at a relatively high speed (up to 1.5 m/s). Both minimalistic visual and sound systems (comprised of only 4 pixels and two 0.1 g omni-directional microphones) suffices for the hovercraft to reach the target while controlling its clearance from the walls and its forward speed jointly, without any need for speed and range sensors.