Override forces through clumps of small vegetation

Vegetation override is an important aspect of off-road ground vehicle mobility. For autonomous ground vehicles (AGV), path-planning in off-road environments may be informed by the predicted resistance of vegetation in the navigation environment. However, there are no prior measurements on the override resistance of small stems ($<$2.5 cm) and groups of small stems on medium-sized ($\approx$1000 kg) vehicles. In this work, a series of override measurements for clumps of small vegetation that are relevant for off-road navigation by intermediate-sized AGV is presented. The development and calibration of a custom-made pushbar system with integrated load cells for directly measuring override forces is also presented, and a comparison of the results of the experiments to models developed for override of larger single stems is made. It is found that for clumps of small vegetation, the total override force is best predicted by the diameter of the largest stem in the clump. Additionally, it is found that the equations developed for larger stems under-predict the override forces exerted by smaller stems by about a factor of two.