Design, Modeling, and Control of a Wheel-Legged Locomotion System for the Environmental Hybrid Robot

Gustavo Freitas, Fernando Lizarralde, Liu Hsu, Vitor Paranhos, Ney R. Salvi dos Reis, and Marcel Bergerman


Mobile Robots, Parallel Mechanisms, Hazardous Environments, Environmental Robotics


Urucu, deep in the Amazon forest, is the largest in-land natural gas and oil producing site in Brazil. The oil and gas extracted in Urucu travel some 700 km in a pipeline through the jungle until they reach Manaus, where they are refined and consumed. Exploration of the site is conditioned on the Brazilian oil company Petrobras monitoring a 400 km section of the pipeline for any signs of water contamination. The Environmental Hybrid Robot (EHR) was conceived to automate this humongous monitoring task, currently executed in extremely small scale by scientists and locals on foot and small boats. This paper describes the design, analysis, and testing of the EHR's second-generation locomotion mechanism, based on a two-DOF parallel mechanism. The new mechanism allows for independent control of wheel position and orientation relative to the terrain, thus significantly increasing the robot's mobility. Additionally, it allows for control of the vehicle's velocity-torque curve by adjusting the radius of curvature of the wheel at the point of contact with the soil. We present the forward and differential kinematic models of the new mechanism and, based on them, a differential kinematics-based position and orientation control method. We illustrate the methodology with experimental results.

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