Introduction to RoboticsLocomotion CSCI 4830/7000 January 11, 2010 NikolausCorrell
What is locomotion? Latin: moving from place to place Crawling Sliding Running Jumping Walking Rolling
Other forms of locomotion Swimming Gliding Flying Propulsion
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.
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
Walking vs. rolling If the terrain allows, rolling is more efficient Walking requires more Structural complexity Joints Control
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 stability 6 legs : static walking
Walking 2-DOF 4-DOF 6-DOF How many DOF are needed?
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!
Horse Gait (Gallop) 167 different gaits observed in a horse!
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=FAcgSi6pzv4 http://www.youtube.com/watch?v=CD2V8GFqk_Y
Wheeled locomotion Most appropriate for most applications Stable with at least 3 wheels Steered wheels make control more complex pretty quickly Stable zone
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
Omni-Directional Drive Swedish Wheel Rotation around wheel axle Rotation around the rollers Rotation around contact point Uranus, CMU
Climbing with wheels Friction-based Center-of-gravity based Suspension-based
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
Part II: Practice
Brushed DC Motor Directly driven by DC current Self-commutating Speed regulated by voltage Needs gear-box to generate useful speed/torque
Stepper Motor Requires dedicated circuitry to generate activation sequence Speed of sequence controls motor speed Motor stops at precise increments
Brushless DC Motor Commutation done electronically Requires speed controller More efficient then brushed DC Motor
Encoders Required to estimate axis position Optical encoders Differential Quadrature Absolute Hall-Effect
Servos Servo =motor + encoder + gearbox + controller Low-End: Pulse-Width Modulation (PWM):rate regulates position High-End: Digital control allows setting and querying position, speed and torque
Design Lets design robots that Crawl Slide Gallop Jump Walk Roll Crawling Sliding Running Jumping Walking Rolling
Crawling Mechanics of Soft Materials Laboratory http://ase.tufts.edu/msml/researchInchBot.asp
Sliding Gavin Miller Hirose-Fukushima lab http://www-robot.mes.titech.ac.jp/robot_e.html
Running Scout II, McGill University http://www.youtube.com/watch?v=SRIU7PtyGOw
Jumping Laboratory of Intelligent Systems, EPFL http://lis.epfl.ch/?content=research/projects/SelfDeployingMicroglider/
Homework Chapter 3 Required for next week’s exercise Hints read the questions first Skip: 220.127.116.11-5 Skim: 3.2.4-3.3.3 Understand what Maneuverability (Mobility and Steerability is) conceptionally Goal: calculate the speed of your robot’s motors so that it can follow a desired trajectory
Next exercise Locomotion (1 week) Play with different locomotion concepts in Webots Understand various gaits Come up with a “stand-up-gait” for the Soccer robot