Design of a spider-like robot for motion with quasistatic force constraints

This paper presents a novel design of a 4-legged 'spider' robot capable of moving in a wide range of two-dimensional tunnels. The spider moves in a quasistatic manner, by stably bracing itself against the tunnel walls and moving a free limb to a new position. The design has been strongly influenced by the recent immobilization theory of Rimon and Burdick. The theory dictates the minimum number of limbs such a spider can have, as well as the shape of the footpads. The class of tunnel geometries dictates other key parameters of the spider, such as limb dimensions and number of degrees of freedom of each limb. We review the relevant components of the immobilization theory, then describe the details of the spider design. The spider will initially move under a worst-case assumption of slippery tunnel walls, and we also describe a locomotion strategy under this assumption. The spider has been built and is currently undergoing locomotion experiments.