Mechanics of Off-the-Road Locomotion

Abstract

Off-the-road locomotion has always been, an important part of technology and economics. Yet it has never been treated within a comprehensive theoretical approach. Space research, and in particular preparations for the exploration of the surface of the moon, have in a sense dramatized the issue. As the trial and error method is not applicable in the latter case, theoretical work and research in simulated lunar conditions have already started. New emphasis on off-road mobility on this planet, stressed from commercial and military viewpoints, has also contributed to the growing interest in this area. Early work on the mechanics of off-the-road locomotion started in 1913 in Germany and in 1943 in England, and laid the first cornerstones for a theoretical approach. The solid foundation for the development of the mechanics of soil-vehicle relationship, however, was first established between 1944 and 1950 in Canada. On that foundation the first general outline of a theory which covers all the physical phenomena pertaining to terrain-vehicle systems was completed in the United States around 1960. The results of this work were the main theme of the First International Conference on the Mechanics of Terrain-Vehicle Systems held in Italy in 1961. The theory is based on the Coulombian criterion of soil failure which relates to thrust, and on semi-empirical moduli of sinkage which relate to the motion resistance. It constitutes a working tool for engineers and planners and offers a general methodology for the further development of mathematical equations needed in the prediction of vehicle performance and design parameters. The accuracy of such predictions so far achieved is encouraging, although much improvement is necessary. These new methods enable the user and designer of motor vehicles to have a much better understanding of the relative merit of various types of locomotion in various environments. They have laid a foundation for the more rational planning of vehicle development and the evaluation of design trends, and the preliminary optimization of terrain-vehicle systems in randomly changing conditions due to climate and geography has been made possible. Long range evaluation of future trends in off-the-road locomotion indicate that the so-called articulated vehicles, composed of a number of self-propelled units linked together by free steerable joints, in a manner similar to a railroad train, offer great promise. Future progress is seen in terrain measurement, in the analysis of terrain-vehicle relations from the viewpoints of performance and design, and in research aiming at the improvement of the present theories.