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Analysis of the effect of soft soil’s parameters change on planetary vehicles’ dynamic response

Shibly H.

Journal of Automation Mobile Robotics and Intelligent Systems

2017

Vol. 11, No. 4

65--72

The mobility of a planetary vehicle has numerous constraints imposed by the types of terrain. Navigation is difficult through uneven and rocky terrain, and becomes worse due to abrupt changes of ground level which may cause a fall to a lower ground level. This article examines the effect of the soil’s parameters change due to repetitive falls on the vehicle’s dynamic behavior. After each free fall of the vehicle there is a collision of the vehicle’s wheel with the ground. If the ground is made up of soft soil there is an increase in the soil compactness after each collision. The increase in the soil compactness causes a change in the soil parameters. These changes modify the algorithm’s parameters of the vehicle’s dynamic model. The dynamic model is a quarter vehicle model with single rigid wheel which falls on soft soil. Simplified forms of the Pressure-Sinkage models of Bekker and Reece for the sinkage of a rigid body into soft soil are incorporated in the numerical solution of the governing equations of motion. The dynamic interaction of a rigid wheel and soft soil has three stages: sinkage stage, wheel dwell stage, and wheel pullout from soil stage. By comparing the simulations results when the soil’s parameters are kept constant and when their changes are incorporated in the dynamic model showed that the difference in the dynamic response are not significant and can be neglected. There is a gradual change in the dynamic mechanical quantities when the soil’s parameters are kept constant, while the changes in the dynamic mechanical quantities between the second fall and the successive falls are small.

Dynamic Modeling of Planetary Vehicle’s Fall on Soft Soil

Shibly H.

Journal of Automation Mobile Robotics and Intelligent Systems

2016

Vol. 10, No. 3

22--28

The objective of future planetary mission is to explore more new zones on Mars planet. This goal may be achieved by using high speed planetary vehicle, (Rover). The motion of planetary vehicles at high speed and on unknown terrain increases the number of possible risks. One risk is a sudden change of ground level in the vehicle path causes a fall down onto a low ground. This paper presents a study and simulation of the dynamic response of a free fall of a quarter vehicle (rover) model with rigid wheel on a soft soil. A simplification of Bekker’s equation is derived and used in the numerical solution of the two coupled dynamic equations of motion. The Dynamic response of the unsprung mass, rigid wheel, shows a three stages; the sinkage stage, the equilibrium stage, and the pulling out stage from soil. The simulation shows that having rigid body mode helps in pulling out the vehicle wheel from the soil. It shows that the first three stages of the first fall are the most significant ones. They have the largest sinkage, largest impulsive force, and largest amplitude of the system dynamic response during interaction of the rigid wheel and the soft soil following the free fall. The existence of a damping reduces the dynamic response magnitude and prevent the unsprung mass from pulling out the wheel from soil after sinkage.