INVESTIGATION OF STRESS AND FAILURE IN GRANULAR SOILS FOR LIGHTWEIGHT ROBOTIC VEHICLE APPLICATIONS

This paper describes novel experimental methods aimed at understanding the fundamental phenomena governing the motion of lightweight vehicles on dry, granular soils. A single-wheel test rig is used to empirically investigate wheel motion under controlled wheel slip and loading conditions on sandy, dry soil. Test conditions can be designed to replicate typical field scenarios for lightweight robots, while key operational parameters such as drawbar force, torque, and sinkage are measured. This test rig enables imposition of velocities, or application of loads, to interchangeable running gears within a confined soil bin of dimensions 1.5 m long, 0.7 m wide, and 0.4 m deep. This allows testing of small-scale wheels, tracks, and cone or plate penetrators. Aside from standard wheel experiments (i.e., measurements of drawbar force, applied torque, and sinkage during controlled slip runs) two additional experimental methodologies have been developed. The first relies on high-speed imaging of the wheel-soil interface and the use of particle image velocimetry (PIV) to measure micro-scale terrain kinematics. The second experimental methodology consists of a custom force sensor array located at the wheel-terrain interface. The sensors allow explicit measurement of normal and shear forces (and, therefore, estimation of normal and shear stresses) at numerous discrete points along the wheel-soil interface. Experimental measurements gathered by these test methodologies are to be compared against well-established semi-empirical models, to validate and understand limitations of the models and propose improvements.