Why snake robots need torsion-free joints and how to design them

In order to perform operations such as slip-free locomotion and vertical climbing, autonomous snake robots need joints with special properties. The most important of these are their being torsion-free, and having large pitch range. We discuss these requirements, and derive an actuated, torsion-free joint design which combines a /spl plusmn/135/spl deg/ pitch range with an unlimited roll range. The joint has been built and tested, and some data are given for a prototype, employed in an experimental snake robot.