Vision-based flight control and stabilisation in hawkmoths

Thesis

Insects are inherently unstable and therefore rely on sensory feedback in order to maintain flight control and stability. This thesis focuses on how the hawkmoth Manduca sexta uses visual feedback to control and stabilise flight. The analysis is based on extensive sampling of the optomotor responses. I use a virtual reality flight simulator to measure the total moment that the moths generate in response to oscillating wide-field stimuli. The visual stimuli simulate rotations of different amplitudes and frequencies about six different body axes. The moment responses depend upon stimulus amplitude, so are fundamentally non-linear. Nevertheless, for a fixed and suitably small stimulus amplitude, it is possible to fit a linear PID-controller with time delay to each of the optomotor responses. The analysis shows that the moths rely on proportional and integral feedback of angular velocity, with different time delays about different rotation axes. This varying time delay prevents spatial superposition of the optomotor responses to lateral rotational stimuli, meaning that there is no general control law that predicts the responses to an arbitrary lateral stimulus. By combining these empirically derived vision-based flight controllers with linearised flight dynamic models of hovering M. sexta, I evaluate their performance in providing flight stability. This analysis suggests that visual feedback is sufficient to stabilise disturbances associated with rotational stimuli about the horizontal roll and dorso-ventral axes, but is insufficient to stabilise disturbances associated with rotational stimuli about the pitch axis, vertical yaw axis, and longitudinal body axis. The time delay of the optomotor response has a substantial influence on the superposition of the measured optomotor responses, and strongly affects the predicted flight stability. The findings presented in this work have implications for understanding not only the mechanisms and functionality of flight control in hawkmoths, but also the results of past and future investigations into vision-based flight control in insects and flapping-wing air vehicles.

Authors: Müller, T

• DOI: 10.5287/ora-braqzmjrd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Subjects: Flight control; Insects--Flight; flight dynamics; insect vision