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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 noiseØinfrared
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
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