Group 4 2014

Jumping on an Aerated Granular Medium

Group Members: Alex Lind, Cristian Salgueiro, Casey Trimble

Introduction

Granular media are unique in that they can easily transition from solid-like behavior to fluid behavior in response to external conditions. This creates an interesting environment for locomotion in a granular medium, which is a process that utilizes the transfer of force between the locomotive body and the medium. The transition from solid behavior to fluid behavior, or vice versa, can have a large effect on how efficient a method of propulsion is. One way to investigate the nature of force transfer in granular media is to manipulate the parametric constraints that govern the boundary between solid and fluid.

Aerating a granular medium by introducing an air flow from below is one way to accomplish this. By controlling the air flow, it is possible to reduce the amount of force required to reach the fluid regime in the medium. This transition may not be a linear function of air flow, and it is possible that insight could be gained from experiments that test the efficiency of a jumping robot on the medium as the flow rate is increased.

Methods

A container filled with a granular medium (poppy seeds) will be aerated using a blower attached to the bottom through an air duct manifold that distributes an approximately uniform airflow. The flow rate will be controlled externally. Mounted on the surface will be a robot jumper that will be attached to a vertical sliding rod. The appendage of the jumper will be a spring of known spring constant, and the forcing of the jumper will be controlled externally. In later experiments, a controlled variable stiffness spring may be used to further expand the parameter space of the experiments.