Modeling of skid-steer mobile manipulators using spatial vector algebra and experimental validation with a compact loader

The present work models the dynamics of general skid-steer mobile manipulators using the formalism and tools of the spatial vectors algebra introduced by Featherstone. The model built is validated using inertial measurements obtained during field tests with a compact skid-steer loader. The paper demonstrates the benefits of using the spatial vector algebra formulation, showing that this modeling approach allows to integrate traction forces and study the arm-vehicle, as well as vehicle-ground interactions in a single model. This feature is not possible with many other of the existing modeling approaches and simulation tools, thus opens the way to research on mechanically more complex robot designs and their controllers. It is to be noted that most of the existing models and simulations of mobile manipulators consider two-wheeled differentially driven bases and avoid accurate models of skid-steering bases because of the complexity of simulating wheels that skid while rolling. However, skid-steer traction is common in most of the industrial construction and mining machinery because of their simpler mechanics, high reliability, and better mobility in rough terrains. Hence, the development of physically accurate models of skid-steer manipulators is fundamental. We chose to validate the model using a Cat^® 262C compact-skid steer loader instead of a small mobile manipulator common in robotics research laboratory to highlight the usefulness of the presented model and the spatial vector algebra approach.