We developed a very small and light butterfly-type ornithopter (BTO) to investigate butterfly flight. Its weight is 0.4 g, wing span is 140 mm and flapping frequency is 10 Hz. It flies forward passively. The flights were recorded with a highspeed video camera and the longitudinal motion of the BTO was analyzed. When the center of gravity was appropriate, the angle of attack of the body varied cyclically. We found that the cyclical change of the angle of attack produced total upward aerodynamic force. Then we visualized air flow around the BTO both in tethered flight and in free flight. We revealed that free body motion caused a stable attachment of leading edge vortex. We also found that the free body motion helped the wings' smooth upstroke, which was not found in tethered flight.

We investigate the feasibility of the design of a small artificial compound eye that comprises micro-optical, micro-mechanical components and additional electronics for visual processing. The hybrid integration of this "mini-sensor" addresses important issues such as mechanic scale-effect, assembly of small parts and functional testing. The use of retinal scanning for the perception of visual motion is highlighted in the design of a small-sized horizontal array with a scanning retina of 2/spl times/30 photoreceptor elements (R/sub eye/=30 mm). The scanning motion is achieved by actuating the photodiode arrays with a piezoelectric bimorph cantilever beam coupled to a plate spring. The mini-compound eye, equipped with analogue motion detecting circuits, is able to guide the steps of a small mobile platform and perform multi-task visual processing for obstacle avoidance, tracking and pursuit of visual target.