Low-speed optic-flow sensor onboard an unmanned helicopter flying outside over fields

The 6-pixel low-speed Visual Motion Sensor (VMS) inspired by insects´ visual systems presented here performs local 1-D angular speed measurements ranging from 1.5°/s to 25°/s and weighs only 2.8 g. The entire optic flow processing system, including the spatial and temporal filtering stages, has been updated with respect to the original design. This new lightweight sensor was tested under free-flying outdoor conditions over various fields onboard a 80 kg unmanned helicopter called ReSSAC. The visual disturbances encountered included helicopter vibrations, uncontrolled illuminance, trees, roads, and houses. The optic flow measurements obtained were finely analyzed online and also offline, using the sensors of various kinds mounted onboard ReSSAC. The results show that the optic flow measured despite the complex disturbances encountered closely matched the approximate ground-truth optic flow.