Physical experimentation and actuated wheel design for granular locomotion using Resistive Force Theory

Abstract

Physical experiments were conducted using 3D printed wheels and a sand testing bed to explore the applications and predictive power of the Resistive Force Theory (RFT), an empirical model based on linear superposition designed to predict the interactive forces between solid bodies and granular media. Four-spoke wheel designs, made of four treads with a hinge halfway down each tread set to a prescribed angle 0, and cylindrical wheels were used to validate a scaling law determined from RFT. The 3D printed wheels were attached to an experimental test rig that consisted of a motor fixed to a carriage free to move horizontally and vertically. Data was gathered through a series of horizontal, vertical, and angular position sensors and a set of force and torque sensors, then processed with a MATLAB script and determined to validate the RFT scaling law. Next, the design of an actuated wheel capable of altering its shaped while in motion was explored. RFT predicts that as motion conditions of the wheel change, a corresponding change in the shape of the wheel would lead to an improvement in the wheel's performance. In order to properly analyze the effect of the change of shape of the wheel, the actuated wheel was designed to first only change shape in the in-plane dimension, and second be sufficiently rigid such that it does not exhibit excessive deformation in the new shape while under load. Several designs were explored, and the final form of the "FrankenWheel" is designed with a series of five flaps that rotate to fixed angles using a system of gears, hinges, and a secondary motor. This version of the "FrankenWheel" has been assembled for testing.