Local traversability assessment in an unmanned ground vehicle : An analysis of mobility on the UGV Husky

Abstract: This thesis project aims to learn and understand more about implementing a path planner to the unmanned ground vehicle (UGV), UGV Husky, specifically its traversability algorithm, and investigate how it could be further improved. A surrounding grid is generated around the UGV where each cell contains information connected to its traversability. The traversability filter is given this information to score how possible it is to traverse to the cell with regard to angular slope, terrain roughness, and step height. The three parameters have each a critical value that works as a limit where if one of the three parameters were to exceed the critical value then the cell would not be estimated to be traversable. The current problem is that their critical value for angular slope, step height, and terrain roughness are decided arbitrarily and mostly through simulation. To solve this problem, formulas are derived that focus on geometrical aspects of a UGV to define the limits in focus on slope and step. The formulas give threshold values applied to the code and are run in simulation. To validate this, hardware experiments are done to compare simulation and reality. This is to observe and learn if the simulations are good representations of reality and if the threshold values are correct. The results show that the thresholds are good estimations of the UGV Husky's limits. This is if one takes into consideration that other important factors are not included or known, such as the ground conditions in the actual experiments. The simulation studies also prove that Gazebo simulations are not good representations of reality to test terrain difficulties because of simplified physical representation, giving unreliable limits. Based on the successful implementation of the geometrically derived threshold values for slope and step, further work could include similarly derived threshold values for terrain roughness, and attempt to optimize the variables that are in the traversability formula.