Step Climbing Cooperation Primitives for Legged Robots with a Reversible Connection

Cooperation primitives for climbing steps were developed for a system of two 10 cm long VelociRoACH hexapedal legged robots with a removable connection. When performed sequentially, the set of primitives allow the team of two robots to climb a step on the order of their body length. These primitives use a tether between the robots actuated by a winch on one of the robots to form and release connections, run synchronously while connected, and provide a tether assist force while running. For a step with a coefficient of friction of 1 and a height of 6.5 cm, quasi-static analysis correctly predicts that the two connected robots can raise the front robot over the top of the step, while a single robot can only pitch upward against the step. The winch module designed to perform the cooperative climbing experiments meets the system goals of providing controllable forces greater than each robot's body weight while driving a removable connection between the robots. Experiments demonstrate that the robot system can perform each cooperation primitive individually with a reliability of at least 50% using simple strategies of maintaining a constant bounding frequency with the drive motors of each robot and a set tether tension with the winch.