M.Sc Student M.Sc Thesis Mann Moshe Peretz Dynamic Stability of Off-Road Vehicles Department of Mechanical Engineering PROF. Elon Rimon MR Zvi Shiller

Abstract

Of the ever increasingly sophisticated tasks assigned to mobile robots, many require them to traverse over rough, uneven terrain in the minimum amount of time possible. In the course of this traversal, the robot runs the risk of becoming unstable due to sliding, loss of contact with the ground, or tipping over. The stability of the robot is directly affected by its velocity and acceleration,

especially for tasks where time is of the essence. If either exceeds its prescribed bounds, the robot will become unstable. The necessity thus arises to develop stability margins with regard to the admissible speeds and accelerations.

We accomplish that task by devising a static stability margin and a dynamic stability margin, which take the maximum admissible static acceleration and maximum admissible velocity, respectively, as measures of the robot’s stability. This requires an analysis of the dynamics of the robot and its interaction with the terrain, in order to calculate the range of admissible motion. This is

the contribution of this thesis - the development of methods for the computation of the admissible velocities and accelerations of a mobile robot moving over uneven terrain.

The analysis is carried out on a two dimensional longitudinal models for a four wheeled vehicle and for a Rocker Bogie exploration rover traversing general terrain. The dominant feature of the rough terrain for our purposes is its curvature, and so is modelled as a smooth continuous spline.

Several methods are presented for carrying out the above calculation: the numerical method, the geometric method, the vector-algebraic method, and the linear algebraic method. An understanding of the physics that underlie the robot’s stability is provided by the geometric method, while the linear algebraic method generalizes the stability analysis, enabling the computation of stability

margins for more complicated vehicle models.

Simulations are carried out on a virtual Rocker Bogie on several different terrain profiles and vehicle models . The various stability margins that arise from different vehicle models and varying terrain parameters are contrasted to indicate how the physical properties of the contact model affect the results of the simulation. The methods developed are partially extended to motion on three dimensional simulated terrain.