Date of Award

11-2010

Embargo Period

5-20-2011

Degree Name

Doctor of Philosophy (PhD)

Department

Robotics Institute

Advisor(s)

Matthew T. Mason

Second Advisor

Howie Choset

Third Advisor

Christopher G. Atkeson

Fourth Advisor

Kevin M. Lynch

Fifth Advisor

Andy Ruina

Abstract

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 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, openloop
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.

Comments

CMU-RI-TR-10-38

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