Modeling, Analysis, and Control of an Actively Reconfigurable Planetary Rover for Traversing Slopes Covered with Loose Soil

Future planetary rovers are expected to probe across steep sandy slopes such as crater rims where wheel slippage can be a critical problem. One possible solution is to equip locomotion mechanisms with redundant actuators so that the rovers are able to actively reconfigure themselves to adapt to the target terrain. This study modeled a reconfigurable rover to analyze the effects of reconfiguration on rover slippage on sandy slopes. We also investigated control strategies for a reconfigurable rover to reduce slippage. The proposed mechanical model consists of a complete rover model, which represents the relationship between the attitude of the rover and the forces acting on each wheel, and a wheel-soil contact force model, which is expressed as a function of slip parameters. By combining these two models, the proposed model relates the configuration of the rover to its slippage. The reliability of the proposed model is discussed based on a comparison of slope-traversing experiments and numerical simulations. The results of the simulations are similar to those of the experiments and thus verify the proposed model. Following the results, a configuration control strategy for a reconfigurable rover was introduced accompanied by orientation control. These controls were implemented on a four-wheeled rover, and the effectiveness of the controls was tested on a natural sand dune. The results of the field experiments show the usefulness of the proposed control strategies.