  A hover-capable insect-inspired flying robot that can remain long in the air
has shown its potential use for both confined indoor and outdoor applications
to complete assigned tasks. In this letter, we report improvements in the
flight endurance of our 15.8 g robot, named KUBeetle-S, using a low-voltage
power source. The robot is equipped with a simple but effective control
mechanism that can modulate the stroke plane for attitude stabilization and
control. Due to the demand for extended flight, we performed a series of
experiments on the lift generation and power requirement of the robot with
different stroke amplitudes and wing areas. We show that a larger wing with
less inboard wing area improves the lift-to-power ratio and produces a peak
lift-to-weight ratio of 1.34 at 3.7 V application. Flight tests show that the
robot employing the selected wing could hover for 8.8 minutes. Moreover, the
robot could perform maneuvers in any direction, fly outdoors, and carry
payload, demonstrating its ability to enter the next phase of autonomous
flight.
