1,251 research outputs found
The Effect of Internal Damping on Locomotion in Frictional Environments
The gaits of undulating animals arise from a complex interaction of their
central nervous system, muscle, connective tissue, bone, and environment. As a
simplifying assumption, many previous studies have often assumed that
sufficient internal force is available to produce observed kinematics, thus not
focusing on quantifying the interconnection between muscle effort, body shape,
and external reaction forces. This interplay, however, is critical to
locomotion performance in crawling animals, especially when accompanied by body
viscoelasticity. Moreover, in bio-inspired robotic applications, the body's
internal damping is indeed a parameter that the designer can tune. Still, the
effect of internal damping is not well understood. This study explores how
internal damping affects the locomotion performance of a crawler with a
continuous, visco-elastic, nonlinear beam model. Crawler muscle actuation is
modeled as a traveling wave of bending moment propagating posteriorly along the
body. Consistent with the friction properties of the scales of snakes and
limbless lizards, environmental forces are modeled using anisotropic Coulomb
friction. It is found that by varying the crawler body's internal damping, the
crawler's performance can be altered, and distinct gaits could be achieved,
including changing the net locomotion direction from forward to back. We will
discuss this forward and backward control and identify the optimal internal
damping for peak crawling speed
Direct Measurements of Drag Forces in C. elegans Crawling Locomotion
AbstractWith a simple and versatile microcantilever-based force measurement technique, we have probed the drag forces involved in Caenorhabditis elegans locomotion. As a worm crawls on an agar surface, we found that substrate viscoelasticity introduces nonlinearities in the force-velocity relationships, yielding nonconstant drag coefficients that are not captured by original resistive force theory. A major contributing factor to these nonlinearities is the formation of a shallow groove on the agar surface. We measured both the adhesion forces that cause the worm’s body to settle into the agar and the resulting dynamics of groove formation. Furthermore, we quantified the locomotive forces produced by C. elegans undulatory motions on a wet viscoelastic agar surface. We show that an extension of resistive force theory is able to use the dynamics of a nematode’s body shape along with the measured drag coefficients to predict the forces generated by a crawling nematode
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