Slide-Down Prevention for Wheeled Mobile Robots on Slopes

Wheeled mobile robots on inclined terrain can slide down due to loss of traction and gravity. This type of instability, which is different from tip-over, can provoke uncontrolled motion or get the vehicle stuck. This paper proposes slide-down prevention by real-time computation of a straightforward stability margin for a given ground-wheel friction coefficient. This margin is applied to the case study of Lazaro, a hybrid skid-steer mobile robot with caster-leg mechanism that allows tests with four or five wheel contact points. Experimental results for both ADAMS simulations and the actual vehicle demonstrate the effectiveness of the proposed approach.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Analysis of Tread ICRs for Wheeled Skid-Steer Vehicles on Inclined Terrain

The instantaneous centers of rotation (ICRs) for the two treads of skid-steer vehicles moving with low inertia on hard horizontal terrain almost remain with constant local coordinates, which allows to establish an equivalence with differential-drive locomotion. However, this significant kinematic relationship has not been analyzed yet on sloped ground. One relevant difficulty of studying ICR behavior on inclined terrain, even on a flat surface, is the continuous variation of pitch and roll angles while turning. To overcome this problem, this paper analyzes a dynamic simulation of a skid-steer vehicle on horizontal ground where gravity is substituted by an equivalent external force in such a way that pitch and roll are kept constant. Relevant tread ICR variations on inclined ground have been deduced, which have a significant impact on skid-steer kinematics. These new findings have been corroborated experimentally with a four-wheeled mobile robot that turns on an inclined plane.Spanish Project PID2021-122944OB-I0

Evaluation of navigability in skid-steer mobile robots with passive trailers moving on sloping terrain

[EN] The use of trailers allows robots to increase their load capacity to perform multiple tasks, but their use carries multiple risks. In this research, three metrics are developed to assess the navigability of robots with coupled trailers when moving at low speeds on inclined surfaces: an index that predicts the initiation of rollover in the robot or trailers; another index that estimates the start of the total slip due to the slopes of the terrain, either in the robot or the trailers; and finally, an index that quantifies the robot's ability to address itself and follow a path. These three metrics were developed based on the reaction forces of the wheels with the ground and were validated through  simulation and experimental tests using a Skid Steer robot called Lázaro, demonstrating their effectiveness in estimating the risk condition for which they were designed.[ES] El uso de remolques permite a los robots aumentar su capacidad de carga para realizar múltiples tareas, pero su uso conlleva múltiples riesgos. En esta investigación, se desarrollan tres métricas para evaluar la navegabilidad de robots con remolques acoplados cuando se mueven a bajas velocidades sobre superficies inclinadas: un í­ndice que predice el inicio del vuelco en el robot o los remolques; otro í­ndice que estima el inicio del deslizamiento total debido a las inclinaciones del terreno, ya sea en el robot o los remolques; y finalmente, un í­ndice que cuantifica la capacidad del robot para direccionarse y seguir una trayectoria. Estas tres métricas fueron desarrolladas con base en las fuerzas de reacción de las ruedas con el suelo y fueron validados a través de simulación y pruebas experimentales utilizando un robot Skid Steer llamado Lázaro, demostrándose su efectividad al estimar la condición de riesgo para la cual fueron diseñados.Este trabajo ha sido realizado parcialmente gracias al apoyo del Decanato de Investigación de la Universidad Nacional Experimental del Táchira bajo los proyectos No. 01-025-2016 y 01-004-2019.García, JM.; Yánez, P.; Martínez, JE. (2022). Evaluación de la navegabilidad en robots móviles skid-steer con remolques pasivos moviéndose sobre terrenos inclinados. Revista Iberoamericana de Automática e Informática industrial. 20(1):13-24. https://doi.org/10.4995/riai.2022.17161132420