Meeting Abstract

25.4  Saturday, Jan. 4 14:15  Jumping off flowable ground AGUILAR, JJ*; GOLDMAN, DI; Georgia Institute of Technology; Georgia Institute of Technology jjaguilar1@gmail.com

Many organism behaviors such as sprinting, jumping and hopping involve impulsive ground interactions. On hard ground, these behaviors can be described as transient bursts of actuation coupled with internal elastic elements to create movement. On flowable ground like granular media, however, the performance of these behaviors changes due to the dynamical ground reaction forces generated by substrate yielding upon foot intrusion. The relationships that govern these forces vary with size and shape of foot, material compaction and speed/acceleration of intrusion; however, we do not have detailed understanding of such interactions. To remedy this, we study the performance of an actuated spring mass robot during vertical jumping on granular media. The robot consists of a linear motor in series with an elastic element coupled to a foot with varied shapes. The robot performs jumps via one-cycle sinusoidal internal movement. We record jump height using a high speed camera, and control the substrate properties using an air-fluidized bed. We systematically vary the forcing frequency (0 to 12 Hz) and the compaction (volume fraction 0.58 to 0.63) and find that, at 8 Hz forcing, there is 743% increase in jump height with only a 5% increase in volume fraction using a 5 cm foot. Including a short, high speed downward push, or “preload”, prior to the main sine-wave movement nearly doubles the jump height at high volume fractions. A depth dependent intrusion force model captures some features of the experiment: reduced height compared with hard ground and optimal jumping when forced near mass-spring resonance. However, the model cannot describe how the jump height changes with compaction and foot size, and is unable to match experimental preloaded jump heights, suggesting nontrivial dependence on intrusion kinematics.