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May 10, 2000 1
Multi-Robot Interactions6.836 Embodied Intelligence
Karen Zee Eugene Shih Allen Miu
May 10, 2000 2
Introduction
Project Goals Multi-robot
interactions Behavior-based
approach Following
Constraints Autonomous No global control
May 10, 2000 3
Outline
Project considerations Robot Anatomy Software Architecture Refinement of the Robot Demonstration Conclusion
May 10, 2000 4
Project considerations
Goal requirements Desired behaviorswMobilewRecover from collisionsw Find and follow
Practical constraints Time Cost Availability of parts Preserve our own sanity
May 10, 2000 5
Robot Anatomy
Bump sensors
Ranging sensor
Tracking sensors
Microcontroller
Beaconemitter
May 10, 2000 6
The Robot Brain
Minimum requirements Enough analog and digital inputs for
interfacing sensors Enough outputs to drive motors and generate
signals Low power Small footprint
Many choices available, we considered: Compaq Robot Controller Card LEGO Mindstorms RCX MIT Handy Board
May 10, 2000 7
Drive train
Two wheel differential drive with a passive castor wheel
DC motor @ 19000 rpm Gear ratio = 375:1 Max speed about a foot per second
May 10, 2000 8
Bump Sensors
Goals Detect collision and the direction of the
collision Absorb impact for the robot
May 10, 2000 9
Tracking Sensors
Goals Detect the presence of another robot Estimate orientation relative to the other robot
to get into a following formation Once in formation, help maintain alignment
Considerations Minimize interference between robots Resilient to ambient noiseinfrared
May 10, 2000 10
Tracking Sensors
Approaches Non-modulated Signal
Strength TriangulationwSuffers from a flat
response curve Beacon Direction
Sensing
May 10, 2000 11
Infrared Experiment
May 10, 2000 12
Other anatomical features
Hardware modulation/demodulation Robustness achieved through modulationw 40 kHz and 125 kHz dual modulation scheme
Reflective infrared ranging sensor Used to maintain distance
Break-beam sensors Used for shaft encoding
May 10, 2000 13
Software Architecture
May 10, 2000 14
Software Architecture (details)
Four primary behaviors Other interesting AFSMs Maintain course Maintain speed
Collision handling
Follow
Seek
Wander
May 10, 2000 15
Refinement of a Robot
Using more and better emitters Adding side panels Orientation of infrared sensors
May 10, 2000 16
Building a Better Follower
Rear-wheel drive makes following difficult Front-wheel drive Better following behavior but harder to follow
May 10, 2000 17
Demonstration
VIDEO(Our Oscar Submission)
May 10, 2000 18
Conclusion
Multi-robot interactions can be achieved using behavior-based techniques
Embodiment of robot strongly impacts following behavior
May 10, 2000 19
Interesting Behaviors
Deadlock Livelock (a.k.a. corners are bad) Fortunately, we have a real world
May 10, 2000 20
Circuit Implementation: Receiving
40 kHz and 125 Hz signals are received by infrared sensor
Sensors filter and demodulate 40 kHz Tone decoders demodulate the 125 Hz
May 10, 2000 21
Circuit Implementation: Transmitting
Generate 40 kHz and 125 Hz signals using two astable multivibrators using inverter pair
May 10, 2000 22
Software Architecture
collisionhandling
follow
seek
wander
s
s
s
shaftencoding
HL motorcontrol
LL motorcontrol
maintaincourse
maintainspeed s
s
s