Meeting Abstract

40.1  Monday, Jan. 5 10:30  Body size limit predictions for mechanically mediated maneuvers JAYARAM, K*; FULL, R.J.; University of California Berkeley; University of California Berkeley kaushikj@berkeley.edu http://scholar.berkeley.edu/kaushikj

In nature, animals perform a variety of maneuvers to negotiate complex terrain and escape from predators. During rapid behaviors, when neural control systems are less effective due to delays or bandwidth constraints, small animals utilize alternative, yet equally effective, mechanically mediated strategies to ensure successful performance. Small locomotors use their bodies to absorb energy during collisions and objects to redirect and deflect their motion. Larger animals cannot use these mechanical strategies without severe injuries, because viscoelastic body elements are size-dependent. Here, we present a model for scaling of body mechanics assuming Kelvin-Voigt behavior. Assuming dynamic similarity for the scaling of body velocity as a function of mass (M), we expect velocity to scale as M^0.16, closely agreeing with data on the maximum running speed of animals at M^{0.17± 0.04}. Thus, possible kinetic energies relative to body mass (KE_max) increase according to the power law M^1/3. We find the ability to dissipate energy per unit mass (EA_max), calculated as a product of the material toughness and cross-section area of the animal, is also size-dependent, (M^-1/3), placing small animals at a definite advantage. KE_max and EA_max functions intersect showing that beyond a critical body mass (∼1 kg), the animal’s entire kinetic energy cannot be fully dissipated without undergoing irreversible plastic deformation. Therefore, we predict that animals smaller than 1 kg can employ mechanically mediated maneuvers. Although collisions with objects appears to be an inelegant control strategy, relying on the robustness of a body’s mechanical systems represents a paradigm shift for understanding control in both small animals and robots.