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Minimalistic Dynamic Climbing

Amir Degani
CMU-RI-TR-10-38, Robotics Institute, Carnegie Mellon University, November, 2010

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Dynamics in locomotion is highly useful, as can be seen in animals and is becoming apparent in robots. For instance, chimpanzees are dynamic climbers that can reach virtually any part of a tree and even move to neighboring trees, while sloths are quasistatic climbers confined only to a few branches. Although dynamic maneuvers are undoubtedly beneficial, only a few engineered systems use them, most of which locomote horizontally. This is because the design and control are often extremely complicated. This thesis explores a family of textit{dynamic climbing} robots which extend robotic dynamic legged locomotion from horizontal motions such as walking, hopping, and running, to vertical motions such as leaping maneuvers. The motion of these dynamic robots resembles the motion of an athlete jumping and climbing inside a chute. Whereas this environment might be an unnavigable obstacle for a slow, quasistatic climber, it is an invaluable source of reaction forces for a dynamic climber. The mechanisms described here achieve dynamic, vertical motions while retaining simplicity in design and control. The first mechanism called DSAC, for Dynamic Single Actuated Climber, comprises only two links connected by a single oscillating actuator. This simple, open-loop oscillation, propels the robot stably between two vertical walls. By rotating the axis of revolution of the single actuator by 90 degrees, we also developed a simpler robot that can be easily miniaturized and can be used to climb inside tubes. The DTAR, for Dynamic Tube Ascending Robot, uses a single continuously rotating motor, unlike the oscillating DSAC motor. This continuous rotation even further simplifies and enables the miniaturization of the robot to enable robust climbing inside small tubes. The last mechanism explored in this thesis is the ParkourBot, which sacrifices some of the simplicity shown in the first two mechanism in favor of efficiency and more versatile climbing. This mechanism comprises two efficient springy legs connected to a body. We use this family of dynamic climbers to explore a minimalist approach to locomotion. We first analyze the open-loop stability characteristics of all three mechanisms. We show how an open-loop, sensorless control, such as the fixed oscillation of the DSAC’s leg can converge to a stable orbit. We also show that a change in the mechanism’s parameters not only changes the stability of the system but also changes the climbing pattern from a symmetric climb to a limping, non-symmetric climb. Corresponding analyses are presented for the DTAR and ParkourBot mechanisms. We finally show how the open-loop behavior can be used to traverse more complex terrains by incrementally adding feedback. We are able to achieve climbing inside a chute with wall width changes without the need for precise and fast sensing and control.

BibTeX Reference
title = {Minimalistic Dynamic Climbing},
author = {Amir Degani},
keyword = {Climbing robots, Dynamic locomotion, Minimalism, Nonlinear analysis, Openloop, Self stability},
school = {Robotics Institute, Carnegie Mellon University},
month = {November},
year = {2010},
number = {CMU-RI-TR-10-38},
address = {Pittsburgh, PA},