Using trajectory oscillation timing improves in-flight odometry based solely on optic flows

• Bergantin Lucia
• Coquet Charles
• Nègre Amaury
• Raharijoana Raharijoana Thibault
• Marchand Nicolas
• Ruffier Franck

Traveled distance estimation is a common problem for robotic applications taking place in unknown environments where GPS is not available. In drones, the presence of weight and computational power constraints leads to the importance of developing odometry strategies based on minimilastic equipment. In this study, we imposed upon a hexarotor to perform up-and-down oscillatory motions while flying forward to test a selfscaled scheme of a visual odometer for the first time. For the odometry, the downward translational optic flow was scaled by the current visually estimated flight height and then mathematically integrated to evaluate the total distance traveled. The self-oscillatory trajectory generated successions of contraction and expansion in the optic flow vector field, which allowed to estimate the flight height of the hexarotor by means of an Extended Kalman Filter. We present three strategies based on sensor fusion that rely on no, precise or rough prior knowledge of the optic flow variations imposed by the sinusoidal trajectory. The rough prior knowledge strategy uses solely the timing of the variations of the optic flow. Tests were performed in a flying arena, where the hexarotor followed a circular trajectory while oscillating up-and-down over about 50m under illuminances of 117lux and 1518lux.