2. What is locomotion? Latin: moving from place to place Crawling Sliding Running Jumping Walking Rolling
3. Other forms of locomotion Swimming Gliding Flying Propulsion
4. 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.
5. 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
6. Walking vs. rolling If the terrain allows, rolling is more efficient Walking requires more Structural complexity Joints Control
7. 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
11. 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
12. Wheeled locomotion Most appropriate for most applications Stable with at least 3 wheels Steered wheels make control more complex pretty quickly Stable zone
13. 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
14. Omni-Directional Drive Swedish Wheel Rotation around wheel axle Rotation around the rollers Rotation around contact point Uranus, CMU
16. 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
18. Brushed DC Motor Directly driven by DC current Self-commutating Speed regulated by voltage Needs gear-box to generate useful speed/torque
19. Stepper Motor Requires dedicated circuitry to generate activation sequence Speed of sequence controls motor speed Motor stops at precise increments
20. Brushless DC Motor Commutation done electronically Requires speed controller More efficient then brushed DC Motor
21. Encoders Required to estimate axis position Optical encoders Differential Quadrature Absolute Hall-Effect
22. 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
30. Homework Chapter 3 Required for next week’s exercise 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: calculate the speed of your robot’s motors so that it can follow a desired trajectory
31. 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
