Flapping wings provide unmatched maneuverability for flying micro-robots. Recent advances in modelling insect aerodynamics show that adequate wing rotation at the end of the stroke is essential for generating adequate flight forces. W e developed a thorax structure using four bar frames combined with an extensible fan-fold wing to provide adequate wing stroke and rotation. Flow measurements on a scale model of the beating wing show promising aerodynamics. Calculations using a simple resonant mechanical circuit model show that piezoelectric actuators can generate SUBcient power, force and stroke to drive the wings at 150 Hz.

A 2 D 0 F res on an t t horax s t T U ct u re signed and fabricated for the MFI project. Miniature piezoelectric PZN-PT unimorph actuators were fabricated and used to drive a four-bar transmission mechanism. T h e current tho,rax design utilizes two actuated four-bars and a spherical joint t o drive a rigid wing. Rotationally compliant flexure joints have been tested with lifetimes over lo6 cycles. Wing spars were instrumented with strain gauges for force measurement and closed-loop wing control.

This paper focuses on the design, fabrication and characterization of unimorph actuators for a microaerial flapping mechanism. PZT-5H and PZN-PT are investigated as piezoelectric layers in the unimorph actuators. Design issues for microaerial flapping actuators are discussed, and criteria for the optimal dimensions of actuators are determined. For low power consumption actuation, a square wave based electronic driving circuit is proposed. Fabricated piezoelectric unimorphs are characterized by an optical measurement system in quasi-static and dynamic mode. Experimental performance of PZT-5H and PZN-PT based unimorphs is compared with desired design specifications. A 1 d.o.f. flapping mechanism with a PZT-5H unimorph is constructed, and 180• stroke motion at 95 Hz is achieved. Thus, it is shown that unimorphs could be promising flapping mechanism actuators.

Abstract

Phytagel media were evaluated as systems to mechanically impede roots of A. thaliana. Studying mechanical properties of Phytagel and exploring the root response to mechanical stimulation can facilitate plant culture and plant development. Breaking strengths of 0.5-2.0% phytagel media were tested by uniaxial compression test. Different phytagel concentrations were set to alter the strength of layers in growth medium. Negative correlations were observed between root length, straightness and medium strength. When roots elongated through soft upper-layer (0.6%), penetration ratio decreased with the increase of lower-layer strength (0.6-1.2%) and all roots couldn't penetrate into lower-layer with concentration ≥1.2%. Roots could grow into soft lower-layer (0.6%) from hard upper-layer (0.6-1.2%), with decreased penetration ratio. When roots grew in soft lower-layer, the growth rate linked with upper-layer strength increased to peak. Roots penetration capability into 1.2% lower-layer was improved by growing plants through moderate layer inserted between soft and hard layer, and roots in 0.8% moderate medium have a significant higher penetration ratio than that in 1.0%. It was concluded that the Phytagel systems studied were suitable for studying the effect of mechanical impedance on the elongation of A. thaliana roots. The medium strength affected root penetration significantly and acclimation can improve root penetration capability.

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