lecture 02: locomotion
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TRANSCRIPT
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Introduction to RoboticsLocomotion
CSCI 4830/7000August 30, 2010
Nikolaus Correll
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Last Lecture
• Robots– Sense– Compute– Actuate– Communicate
• If they don’t they are just automatons (but the boundary is vague)
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Last week’s exercise
• Intro to Webots– How to create a wall– What you see / what the robot sees– Sensors: distance & camera– Physics
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What is locomotion?
• Latin: moving from place to place
Crawling Sliding Running
Jumping Walking Rolling
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Other forms of locomotion
Gliding Flying Swimming
Propulsion
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Locomotion relationships
• Swimming to walking• Walking to rolling• Gliding to flying• Running to jumping
A.J. Ijspeert, A. Crespi, D. Ryczko, and J.M. Cabelguen. From swimming to walking with a salamander robot driven by a spinal cord model. Science, 9 March 2007, Vol. 315. no. 5817, pp. 1416 - 1420, 2007.
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Nature vs. Technology
• Robots become more and more capable of imitating natural locomotion schemes
• Nature did not evolve rotating shafts / rotational joints
Hinge joint Ball and socket joint
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Walking vs. rolling
• If the terrain allows, rolling is more efficient
• Walking requires more– Structural complexity– Joints– Control
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Characterization of locomotion
• Stability– Number of contact points– Center of gravity– Static/Dynamic Stabilization– Inclination of terrain
• Contact– Point vs. Area– Friction vs. grasp
3-Point rule
3 legs : static stability6 legs : static walking
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Walking
2-DOF 4-DOF 6-DOF
How many DOF are needed?
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Gait
• Sequence of event sequence
• Event: leg up or down• Possible number of
gaits N=(2k-1)!• Most efficient gait is a
function of speed!
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Horse Gait (Gallop)
167 different gaits observed in a horse!
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Industry
• 2-legged locomotion– popular because suited to
human environment– hardest to control– Commercial prototypes
• 4-legged locomotion– Not statically stable– Commercial prototypes
• 6-legged locomotion– Statically stable– Forestry
http://www.youtube.com/watch?v=CD2V8GFqk_Y
http://www.youtube.com/watch?v=FAcgSi6pzv4
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Wheeled locomotion
• Most appropriate for most applications
• Stable with at least 3 wheels• Steered wheels make
control more complex pretty quickly
Stable zone
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Wheel suspension
• Suspension consists of a spring and damper
• The damper absorbs shock
• The spring counteracts the shock
• Result: – wheel remains on ground– Better traction– Better control
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Omni-Directional Drive
• Swedish Wheel– Rotation around wheel axle– Rotation around the rollers– Rotation around contact point
Uranus, CMU
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Climbing with wheels
Friction-based Center-of-gravitybased
Suspension-based
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Dynamic Stability
• The system has to move in order not to fall over
• Active balance• Inertia is used to
overcome unstable states
• Examples are– Running– Getting up
Inverted Pendulum
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Design
• Lets design robots that– Crawl– Slide– Gallop– Jump– Walk– Roll
Crawling Sliding Running
Jumping Walking Rolling
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Crawling
Mechanics of Soft Materials Laboratoryhttp://ase.tufts.edu/msml/researchInchBot.asp
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Sliding
Hirose-Fukushima labhttp://www-robot.mes.titech.ac.jp/robot_e.html
Gavin Miller
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Jumping
Laboratory of Intelligent Systems, EPFLhttp://lis.epfl.ch/?content=research/projects/SelfDeployingMicroglider/
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Homework
• Chapter 3– Required for exercise in Week 4– Read till September 13– No class next week!– Hints
• read the questions first• Skip: 3.2.3.4-5• Skim: 3.2.4-3.3.3• Understand what Maneuverability (Mobility and Steerability is) conceptionally
• Goal: determine the speed of your robot’s motors so that it can follow a desired trajectory
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Next exercise
• Locomotion (Wednesday)• Play with different locomotion concepts in
Webots• Understand various gaits and implement your
own