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