polar drift geomagnetic reversal phone localizationtaylorm/16_483f/16.483_6.pdf · •polar drift...
TRANSCRIPT
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• Polar Drift
• Geomagnetic reversal
• Phone Localization
en.wikipedia.org
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• Polar Drift
• Geomagnetic reversal• Chrons are randomly distributed,
most 200k-300k years avg of 450k
• Most reversals 1,000-10,000 years
• Latest: 780,000 years ago
• Phone Localization
Geomagnetic polarity during the last 5M. Dark = periods where the polarity matches today's polarityLight = reversed
en.wikipedia.org
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• Polar Drift
• Geomagnetic reversal
• Phone Localization
http://www.zdnet.com/article/how-google-and-everyone-else-gets-wi-fi-location-data/https://www.quora.com/How-does-WiFi-improve-the-GPS-location
GPS + Cell Towers + Access Point signal strength triangulation
Past: Google Street ViewCurrent: Crowdsourcing!Devices send back location + public SSID & MAC
Note: “GPS acquiring satellites message”
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From last year’s midterm (~12 minutes)
[2 points] To calculate odometry, data from wheel encoders is:• integrated• differentiated • generated• discombobulated
[5 points] In 1-2 sentences, explain the basic principle behind range sensors.
[5 points] Suppose you could operate determine your robot’s position with an external motion tracking system, a GPS unit, or using odometry. In at most 3 sentences, describe the pros and cons of each method.
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Locomotion: Chapter 1
• Enabling robots to move
• Many bio-inspired methods:
– Walk, jump, run, slide, skate, swim, fly, roll
– Exception: Powered wheel
• Human invention
• What’s the benefit?
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Power vs. Attainable Speed
• # of actuators
• Structural complexity
• Control expense
• Efficiency
– Terrain
• Motion of the masses
• Losses
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Key Issues for Locomotion
• Stability
– number and geometry of contact points
– center of gravity
– static/dynamic stability
– inclination of terrain
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Key Issues for Locomotion
• Characteristics of contact
– contact point/path size and shape
– angle of contact
– friction
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Key Issues for Locomotion
• Type of environment
– structure
– medium
• water
• air
• soft or hard ground
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Legged Mobile Robots
• Characterized by a series of point contacts between the robot and the ground.
Adaptability and maneuverability in rough terrain
Power and mechanical complexity
High degrees of freedom
Control system complexity
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Leg Configurations
• What is a DOF?
• Minimum DOF required to move a leg forward?
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Leg Configurations
• A minimum of two DOF is required to move a leg forward
– a lift and a swing motion
• Three DOF for each leg in most cases
• Fourth DOF for the ankle joint
– might improve walking
– additional joint (DOF) increase complexity of design and locomotion control
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“Often clever mechanical design can perform the same operations as complex active control circuitry”
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Examples of 3 DOF Legs
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DARPA Robotics Challenge (2015)
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Legged Robot Control
• Gait control: Leg coordination for locomotion
• The gait is the sequence of lift and release events for the individual legs.
• For a robot with k legs, the total number of distinct event sequences N is:
N = (2k-1)!
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Legged Robot Control
• 2 legs: N = 6
– DD, UD, DD
– DD, DU, DD
– DD, UU, DD
– UD, DU, UD, DU
– UD, UU, UD
– DU, UU, DU
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Legged Robot Control
• 2 legs: N = 6
– DD, UD, DD
– DD, DU, DD
– DD, UU, DD
– UD, DU, UD, DU
– UD, UU, UD
– DU, UU, DU
• 6 legs: N = 11! =39,916,800
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Gaits
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Stotting (also pronking or pronging)
• Quadrupeds, particularly gazelles, where they spring into the air by lifting all four feet off the ground simultaneously
• Some evidence: honest signal to predators that prey animal is not worth pursuing
• Stot is a common Scotsand Geordie verb meaning “bounce” or “walk with a bounce”
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Legged Robot Control
• Cost of transportation:
– How much energy a robot uses to travel a certain distance
– Usually normalized by the robot weight
– Measured in J/N-m
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Cost of Transportation
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Legged Robot Control
• Design to better exploit the dynamics– Natural oscillations of pendula and springs– Dynamics of a double pendulum– Springs can be used to store energy– Passive dynamic walkers
• http://www.youtube.com/watch?v=WOPED7I5Lac
• # of legs?– http://www.wimp.com/thelittledog/
• Model inaccuracies– http://www.youtube.com/user/altiodaltiod?feature=watch
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Wheeled Mobile Robots
• Most popular locomotion mechanism
• Highly efficient
• Simple mechanical implementation
• Balancing is not usually a problem
• Suspension system needed to allow all wheels to maintain ground contact on uneven terrain
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Wheeled Mobile Robots
• Focus is on
– Traction
– Stability
– Maneuverability
– Control
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Wheel Designs
a) Standard wheels
– 2 DOF
b) Castor wheels
– 2 DOF
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Wheel Designs
c) Swedish (Omni) wheels
– 3 DOF
d) Ball or spherical wheel
– 3 DOF
– Think mouse ball
– Suspension issue
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Wheeled Mobile Robots
• Stability of a vehicle is guaranteed with 3 wheel – center of gravity: within the triangle formed by ground
contact points of wheels
• Stability is improved by 4 and more wheels• Bigger wheels allow to overcome higher obstacles
– But require higher torque or reductions in the gear box
• Most arrangements are non-holonomic– require high control effort
• Combining actuation and steering on one wheel makes design complex and adds additional errors for odometry
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Static Stability with Two Wheels
• Achieved by ensuring center of mass is below wheel axis
• Or using fancy balancing
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Motion Control
• Kinematic/dynamic model of the robot
• Model the interaction between wheel and ground
• Definition of required motion
– Speed control
– Position control
• Control law that satisfies the requirements