Challenges for 100 Milligram Flapping Flight

Abstract

Creating insect-scale flapping flight at the 0.1 gram size has presented significant engineering challenges. A particular focus has been on creating miniature machines which generate similar wing stroke kinematics as flies or bees. Key challenges have been thorax mechanics, thorax dynamics, and obtaining high power-to-weight ratio actuators. Careful attention to mechanical design of the thorax and wing structures, using ultra-high-modulus carbon fiber components, has resulted in high-lift thorax structures with wing drive frequencies at 110 and 270 Hz. Dynamometer characterization of piezoelectric actuators under resonant load conditions has been used to measure real power delivery capability. With currently available materials, adequate power delivery remains a key challenge, but at high wingbeat frequencies, we estimate that greater than 400 W/kg is available from PZT bimorph actuators. Neglecting electrical drive losses, a typical 35% actuator mass fraction with 90% mechanical transmission efficiency would yield greater than 100 W/kg wing shaft power. Initially the micromechanical flying insect (MFI) project aimed for independent control of wing flapping and rotation using two actuators per wing. At resonance of 270 Hz, active control of a 2 degrees of freedom wing stroke requires precise matching of all components. Using oversized actuators, a bench top structure has demonstrated lift greater than 1000 $\upmu$N from a single wing. Alternatively, the thorax structure can be drastically simplified by using passive wing rotation and a single-drive actuator. Recently, a 60 mg flapping-wing robot using passive wing rotation has taken off for the first time using external power and guide rails.