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Introduction to Robot Design:

Introduction to Robot Design:. Locomotion and Manipulation. Gui Cavalcanti 5/12/2011. Overview. Locomotion Types of locomotion Stability Locomotion design Models Types of control Gaits Manipulation Compliance Forward kinematics Inverse kinematics. Types of Locomotion. Air Planes

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Introduction to Robot Design:

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  1. Introduction to Robot Design: Locomotion and Manipulation GuiCavalcanti 5/12/2011

  2. Overview • Locomotion • Types of locomotion • Stability • Locomotion design • Models • Types of control • Gaits • Manipulation • Compliance • Forward kinematics • Inverse kinematics

  3. Types of Locomotion • Air • Planes • Helicopters • Ornithopters • Ground • Wheels • Tracks • Legs • Water • Propellers • Fins • Buoyancy Control • Space • Rockets • Inertial Orientation

  4. Stability What makes a hot air balloon stable?

  5. Stability Center of Lift Center of Mass

  6. Stability Lift can be modeled as an always-upward force centered at the COL Mass can be modeled as an always-downward force centered at the COM

  7. Passive Stability

  8. Air Locomotion

  9. Air Locomotion • Planes • Wings are shaped to use forward velocity to generate lift • Control surfaces on wings control orientation changes • Helicopters • Spinning wings (the rotor) are shaped to use rotational velocity to generate lift independent of forward velocity • Many configurations of additional rotors and control of existing rotor blade orientation provide orientation changes • Ornithopters • Flapping, passively-compliant wings deform into airfoils to produce forward velocity and lift at each wingstroke • Shaped tails or differences in wing amplitude control orientation changes

  10. Planes • Design space: • Many existing, robust easy-to-modify RC plane kits to choose from. • Designing one from scratch is still a guess-and-try science • Bare minimum for robot control: Attitude sensing, inertial measurement, flap control • Existing robots: • Global Hawk, Reaper, Predator Predator UAV Global Hawk RC Plane Kit

  11. Plane Stability Center of Lift Center of Drag Center of Mass

  12. Plane Instability

  13. Plane Instability • Center of Drag close to or in front of Center of Lift • Plane always wants to flip end over end • Innate tendency makes the plane incredibly maneuverable • Only computerized control can keep it level • All new fighter planes are robot planes

  14. Helicopters • Design space: • Many existing RC helicopter kits, VERY DIFFICULT to make autonomous. Quadrotors are the way to go. • Designing a classic helicopter from scratch is incredibly difficult, quadrotor much less so • Bare minimum for robot control: Attitude sensing, inertial measurement, fine motor control • Existing robots: • Firescout, Draganflyer, Parrot AR.Drone Parrot AR.Drone Fire Scout Draganflyer III

  15. Helicopter Stability

  16. Helicopter Stability • It seems stable, but… • Huge amount of lift is required to keep a mass in the air • When that lift is redirected, mass both: • Drops • Moves sideways very quickly • Helicopters need to constantly vary throttle to stay level while maneuvering

  17. Ornithopters • Design space: • Mechanical design hasn’t even been nailed down yet (though RC toys exist), good luck making a robot out of one. On the other hand, you could get a thesis out of it… • Bare minimum for robot control: …? • Existing robots: • MIT Robot Locomotion Group Ornithopter Project, FestoOrnithopter FestoOrnithopter SkybirdOrnithopter

  18. Ground Locomotion

  19. Ground Locomotion • Wheels • One or more wheels are used to roll over terrain. Multiple wheels, body configurations and suspension used to cover broken terrain. • Turning wheels in place or spinning wheels in opposite directions used to control orientation • Tracks • Tracks composed of multiple links wrapped around pulleys and form one continuous mobile surface • Spinning tracks in opposite directions used to control orientation • Legs • One or more legs are used to step over terrain. Multiple legs and control styles are used to cover broken terrain. • Stepping in an appropriate pattern used to control orientation

  20. Wheels • Design space: • Tons and tons and tons and tons of wheeled robot kits. Lots of fun design space – 95% of kits can’t make it over any terrain, though. • Designing a wheeled vehicle is incredibly easy, and designing one for rough terrain is both fun and relatively simple. • Bare minimum for robot control: None. • Existing robots: • NASA rovers, Crusher, DARPA Grand Challenge cars, 80% of hobby robot kits Crusher Spirit Rover 3pi

  21. Design Exercise! • How do you design a wheeled vehicle to traverse a bump as large as its wheels?

  22. Tracked • Design space: • Very few tracked robot kits, but it is possible to make your own using simple components. • Designing a real tracked vehicle requires a lot of time and manufacturing, but can be done. Taking some shortcuts can simplify the process. • Bare minimum for robot control: None. • Existing robots: • Ripsaw, Packbot, MAARS, Talon, many Battlebots Ripsaw Packbot MAARS

  23. Design Exercise! • What happens to a tracked vehicle trying to traverse the same bump from the previous question?

  24. Design Question? • Why would you pick tracks over wheels, or vice versa?

  25. Ripsaw

  26. Packbot

  27. Legs • Design space: • Small is easy, big is hard. There are tons of little robot kits, but they’ll all cost a lot of money since they use so many motors. • Designing a 6-legged walker is challenging and pays off; designing a 4-legged walker is hard but can be done; designing a 2-legged walker is a total pain to get right. • Bare minimum for robot control: All joint positions, to an exacting degree. • Existing robots: • BigDog, Asimo, Phoenix Hexapod, Bioloid, many legged hobby robotics kits Asimo BigDog Phoenix Bioloid

  28. Legged Locomotion Topics • Polygon of Support and Center of Pressure • Dynamic and Static Balance • Force control and position control • Spring-Loaded Inverted Pendulum (SLIP) • Gaits

  29. Polygon of Support/Center of Pressure • Polygon of Support: • The stable shape defined by the outer edges of a body’s contact with the ground • Center of Pressure: • The center of force from the ground, pushing up on a body

  30. Dynamic Balance/Static Balance • Static Balance: • Keeping your center of mass projected onto your polygon of support, and your center of pressure as aligned with your center of mass projection as possible. • Dynamic Balance: • Relying on multiple footfalls or a dynamically changing center of pressure to maintain balance.

  31. Force Control/Position Control • Position control: • Control of trajectories and exact positions at all times, with forces and velocities resulting from desired positions • Force control: • Control of force at all times, with positions and velocities resulting from desired forces • What do we do as human beings?

  32. Inverted Pendulums

  33. Gaits • Gait: • What legs you put down in what order

  34. Gaits

  35. Design Challenge! • Design a gait for a four-legged animal and execute it. • Design a gait for a six-legged animal and execute it. • Fastest team to run the length of the building outside wins. • Rules: • Team must stay a cohesive, connected whole throughout the entire run • Footfall patterns must be repeated throughout the run. No changing gaits on the fly! • Teams get three attempts per animal type

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