ROBOT WITH STIFF LEGS Anca Elena Cocosco

Abstract

Over half of earth's dry surface is inaccessible to wheeled or tracked vehicles. Even relatively structured indoor or urban environments with steps, stairs, or narrow hallways, are challenging for most wheeled or tracked ssytems. This is one of hte primary motivations for hte study of mobile robots with legs. We propose a new type of quadruped robot with maximum mechanical simplicity - the SCOUT class. Most robots built to date possess many actuated degrees of freedom (DOF) (three or four per leg) thus making them too expensive for practical use. SCOUT robots, on teh other hand, feautre only one actuated degree of freedom per leg. SCOUT dynamics, while still non-trivial, is greatly simiplified compared to that of higher degree of freedom robots. In our anlysis, we assume instantaneous plastic impacts occur when a leg touches the ground, and consequently, a momentu, transfer occurs that causes step changes in the linear and angular velocities. The calculations of these changes are based on the principle of conservation of angular momentum with respect to the impact toe, since it is that point which acts as pivot, or a free pin joint. A set of walking algorithms based on the controlled momentum transfer have been developed, and validated, using numerical simulations. These algorithms have subsequently been implemented on our walking robots, SCOUT I and SCOUT II. This thesis will show that, with very simple mechanical design and control strategies, stable walking is achievable. However, it is important to note that research currently being undertaken in the ARL group will establish that, with only minimal structure chanes, SCOUT will have the ability to run and climb stairs.