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Lecture 02: Locomotion


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Lecture 02: Locomotion

  1. 1. Introduction to RoboticsLocomotion<br />CSCI 4830/7000<br />January 11, 2010<br />NikolausCorrell<br />
  2. 2. What is locomotion?<br />Latin: moving from place to place<br />Crawling<br />Sliding<br />Running<br />Jumping<br />Walking<br />Rolling<br />
  3. 3. Other forms of locomotion<br />Swimming<br />Gliding<br />Flying<br />Propulsion<br />
  4. 4. Locomotion relationships<br />Swimming to walking<br />Walking to rolling<br />Gliding to flying<br />Running to jumping<br />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.<br />
  5. 5. Nature vs. Technology<br />Robots become more and more capable of imitating natural locomotion schemes<br />Nature did not evolve rotating shafts / rotational joints<br />Hinge joint<br />Ball and socket joint<br />
  6. 6. Walking vs. rolling<br />If the terrain allows, rolling is more efficient<br />Walking requires more<br />Structural complexity<br />Joints<br />Control<br />
  7. 7. Characterization of locomotion<br />Stability<br />Number of contact points<br />Center of gravity<br />Static/Dynamic Stabilization<br />Inclination of terrain<br />Contact<br />Point vs. Area<br />Friction vs. grasp<br />3-Point rule<br />3 legs : static stability<br />6 legs : static walking<br />
  8. 8. Walking<br />2-DOF<br />4-DOF<br />6-DOF<br />How many DOF are needed?<br />
  9. 9. Gait<br />Sequence of event sequence<br />Event: leg up or down<br />Possible number of gaits N=(2k-1)!<br />Most efficient gait is a function of speed!<br />
  10. 10. Horse Gait (Gallop)<br />167 different gaits observed in a horse!<br />
  11. 11. Industry<br />2-legged locomotion<br />popular because suited to human environment<br />hardest to control<br />Commercial prototypes<br />4-legged locomotion<br />Not statically stable<br />Commercial prototypes<br />6-legged locomotion<br />Statically stable<br />Forestry<br /><br /><br />
  12. 12. Wheeled locomotion<br />Most appropriate for most applications<br />Stable with at least 3 wheels<br />Steered wheels make control more complex pretty quickly<br />Stable zone<br />
  13. 13. Wheel suspension<br />Suspension consists of a spring and damper<br />The damper absorbs shock<br />The spring counteracts the shock<br />Result: <br />wheel remains on ground<br />Better traction<br />Better control<br />
  14. 14. Omni-Directional Drive<br />Swedish Wheel<br />Rotation around wheel axle<br />Rotation around the rollers<br />Rotation around contact point<br />Uranus, CMU<br />
  15. 15. Climbing with wheels<br />Friction-based<br />Center-of-gravity<br />based<br />Suspension-based<br />
  16. 16. Dynamic Stability<br />The system has to move in order not to fall over<br />Active balance<br />Inertia is used to overcome unstable states<br />Examples are<br />Running<br />Getting up<br />Inverted Pendulum<br />
  17. 17. Part II: Practice<br />
  18. 18. Brushed DC Motor<br />Directly driven by DC current<br />Self-commutating<br />Speed regulated by voltage<br />Needs gear-box to generate useful speed/torque<br />
  19. 19. Stepper Motor<br />Requires dedicated circuitry to generate activation sequence<br />Speed of sequence controls motor speed<br />Motor stops at precise increments<br />
  20. 20. Brushless DC Motor<br />Commutation done electronically<br />Requires speed controller<br />More efficient then brushed DC Motor<br />
  21. 21. Encoders<br />Required to estimate axis position<br />Optical encoders<br />Differential<br />Quadrature<br />Absolute<br />Hall-Effect<br />
  22. 22. Servos<br />Servo =motor + encoder + gearbox + controller<br />Low-End:<br />Pulse-Width Modulation (PWM):rate regulates position<br />High-End:<br />Digital control allows setting and querying position, speed and torque<br />
  23. 23. Linear Actuators<br />Rotation-based<br />Hydraulic / Pneumatic<br />Solenoid<br />Piezo-Electric<br />Shape-Memory Alloy (SMA) wires<br />
  24. 24. Design<br />Lets design robots that<br />Crawl<br />Slide<br />Gallop<br />Jump<br />Walk<br />Roll<br />Crawling<br />Sliding<br />Running<br />Jumping<br />Walking<br />Rolling<br />
  25. 25. Crawling<br />Mechanics of Soft Materials Laboratory<br /><br />
  26. 26. Sliding<br />Gavin Miller<br />Hirose-Fukushima lab<br /><br />
  27. 27. Running<br />Scout II, McGill University<br /><br />
  28. 28. Jumping<br />Laboratory of Intelligent Systems, EPFL<br /><br />
  29. 29. Rolling<br /><br />
  30. 30. Homework<br />Chapter 3<br />Required for next week’s exercise<br />Hints<br />read the questions first<br />Skip:<br />Skim: 3.2.4-3.3.3<br />Understand what Maneuverability (Mobility and Steerability is) conceptionally<br />Goal: calculate the speed of your robot’s motors so that it can follow a desired trajectory<br />
  31. 31. Next exercise<br />Locomotion (1 week)<br />Play with different locomotion concepts in Webots<br />Understand various gaits<br />Come up with a “stand-up-gait” for the Soccer robot<br />