This paper presents an algorithm, called PCG, for planning the foothold positions of spider-like robots in planar tunnels bounded by piecewise linear walls. The paper focuses on 3-limb robots, but the algorithm generalizes to robots with a higher number of limbs. The input to the PCG algorithm is a description of a tunnel hauing an arbitrary piecewise linear geometry, a lower bound on the amount of fnction at the contacts, as well as start and target foothold positions. Using efficient conuex

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... ogramming techniques, the algorithm approximates the possible foothold positions as a collection of cubes in contact c-space. A graph structure induced b y the cubes has the property that its edges represent feasible motion between neighboring sets of 3-limb postures. This motion is realized by lifting one limb while the other two limbs brace the robot against the tunnel walls. A shortest-path search along the graph yields a 3-2-3 gait pattern that moues the robot from start to target using a minimum number of foothold exchanges. Simulation results demonstrate the PCG algorithm in a tunnel environment.