multi-robot interactions - higher...

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