Meeting Abstract

6.4  Thursday, Jan. 3  Morphological and mechanical asymmetry in a biological gyroscope. GEIGER, M.J.*; FOX, J.L.; MYHRVOLD, C.A.; DANIEL, T.L.; Univ.Washington, Seattle; Univ.Washington, Seattle; Pinceton Univ., Princeton; Univ.Washington, Seattle danielt@u.washington.edu

Flies rely on mechanosensory input from reduced hindwings known as halteres to perform complex maneuvers. We are interested in how the mechanical properties of such sensory structures may filter information available to the nervous system. A morphological analysis of these structures in the crane fly Holorusia rubiginosa shows a pronounced dorso-ventral flattening. Given that halteres are driven in the dorso-ventral plane and subject to Coriolis forces in the orthogonal plane, this asymmetry suggests a structural tuning for gyroscopic function. To examine this issue we (1) measured the cross-sectional dimensions of halteres to quantify the asymmetry; (2) performed static bending experiments to determine the flexural stiffness of halteres in the orthogonal planes of motion; and (3) measured the resonant frequency and damping responses to rapid force perturbation in the two orthogonal planes. We found that halteres are strongly asymmetric, with a nearly 2:1 ratio of shaft diameters in the two planes. A consequence of this elliptical shape is a measured flexural stiffness that is 2.6 times less in the driven plane than in its orthogonal direction. Interestingly, halteres show resonance at frequencies far greater than the driven frequency of 40 Hz and damp extremely rapidly. These structural and mechanical asymmetries suggest that during complex maneuvers, the deflection of the halteres will be substantially different in the two planes. We used high-speed digital videography of freely flying crane flies to document the kinematics of halteres and examine the correlations between haltere stroke plane and body rotations. Body rotations lead to bending motions of halteres in a plane that is orthogonal to the dorso-ventral plane.