Control

Material taken from RobotSubsumption.pdf and SumoBot : Mini-Sumo Robotics

Remember Where Are We Going?

Sumo-Bot competitions

Controlling Robot Movement Based on Photo-Resistor Readings' -----[ Constants ]---------------------------------------LeftDark CON 108RightDark CON 114LeftWhite CON 20RightWhite CON 22' Average Scale factorLeftThreshold CON LeftWhite + LeftDark / 2 RightThreshold CON RightWhite + RightDark / 2 ' -----[ Variables ]----------------------------------------timeLeft VAR WordtimeRight VAR Word' -----[ Main Routine ]------------------------------------DO GOSUB Test_Photoresistors GOSUB NavigateLOOP

Code' -----[ Subroutine - Test_Photoresistors ]--------------Test_Photoresistors: HIGH 6 ' Left RC time measurement. PAUSE 3 RCTIME 6,1,timeLeft HIGH 3 ' Right RC time measurement. PAUSE 3 RCTIME 3,1,timeRightRETURN

Code' -----[ Subroutine - Navigate ]--------------------------Navigate: IF (timeLeft < LeftThreshold) AND (timeRight < RightThreshold)

THEN PULSOUT 13, 650 PULSOUT 12, 850 ELSEIF (timeLeft < LeftThreshold) THEN PULSOUT 13, 800 PULSOUT 12, 600 ELSEIF (timeRight < RightThreshold) THEN PULSOUT 13, 600 PULSOUT 12, 800 ELSE PULSOUT 13, 850 PULSOUT 12, 650 ENDIF PAUSE 20 RETURN

Finite State Machine (FSM) Representation

Read photo- resistors

backup turn right turn left go forward

both lowright low

left lowboth high

Controlling Robot Movement Based on Proximity

' {$STAMP BS2} ' {$PBASIC 2.5}' -----[ Variables ]-----------------------------------irDetectLeft VAR BitirDetectRight VAR BitpulseCount VAR Byte

Code

' -----[ Main Routine ]-----------------------------------DO GOSUB Read_IR IF (irDetectLeft = 0) AND (irDetectRight = 0) THEN GOSUB Forward_Pulse ELSEIF (irDetectLeft = 0) THEN GOSUB Turn_Left ELSEIF (irDetectRight = 0) THEN GOSUB Turn_Right ELSE GOSUB Forward_Pulse ENDIF LOOP

Code

' -----[ Subroutines ]-------------------------------------Read_IR: FREQOUT 8, 1, 38500 irDetectLeft = IN9 FREQOUT 2, 1, 38500 irDetectRight = IN0

Code

' -----[ Subroutines ]--------------------------------------Forward_Pulse: PULSOUT 13, 850 PULSOUT 12, 650 PAUSE 20RETURN

Turn_Left: PULSOUT 13, 650 PULSOUT 12, 650 PAUSE 20RETURN

Code' -----[ Subroutines ]--------------------------------------Turn_Right: PULSOUT 13, 850 PULSOUT 12, 850 PAUSE 20RETURN

Back_Up: PULSOUT 13, 650 PULSOUT 12, 850 PAUSE 20RETURN

Finite State Machine (FSM) Representation

Read IR Go forward turn left turn right go forward

Obj forwardObj right

Obj leftNo Obj

How to Put It Together?

Read IR Go forward turn left turn right go forward

Obj forwardObj right

Obj leftNo Obj

Read photo- resistors

backup turn right turn left go forward

both lowright low

left lowboth high

Possible Problems

Jerky or halting movement Chase object over boundary More?

Possible Solution

o Subsumption ArchitectureA programming process by which one behavior subsumes, or over-rides another based on an explicit priority that we have defined. First described by Dr. Rodney Brooks in "A robust layered control system for a mobile robot,” IEEE Journal of Robotics and Automation., RA-2, April, 14-23, 1986.

o FSM with exit conditionso Optimize PBasic control commands

FSM

read IRand set nextStatevariable

read Photoresistorsand set nextStatevariable

check nextStatevariable and branch

Go forward

Go backwards

turn teft

turn right

Alternative FSM

read Photoresistorsand set nextStatevariable

check nextStatevariable and branch

Read IR Go forward turn left turn right go forward

backup turn right turn left go forward

New PBasic Control Commands

BRANCH value, (Case_0, Case_1, Case_2)

is equivalent to:

Test_Value: IF (value = 0) THEN Case_0

' value = 0: go to label "Case_0" IF (value = 1) THEN Case_1

' value = 1: go to label "Case_1" IF (value = 2) THEN Case_2

' value = 2: go to label "Case_2"

New PBasic Control Commands

LOOKUP Index, (Value0, Value1, ...ValueN), Variable

Find the value at location Index and store it in Variable. If Index exceeds the highest index value of the items in the list, Variable is left unaffected.

LOOKDOWN Target, {ComparisonOp} [Value0, Value1, ...ValueN], Variable

Compare Target value to a list of values and store the index number of the first value that matches into Variable. If no value in the list matches, Variable is left unaffected. The optional ComparisonOp is used as criteria for the match; the default criteria is "equal to."

The ImplementationlineBits VAR NiblineLeft VAR lineBits.Bit1lineRight VAR lineBits.Bit0Main: GOSUB Read_Line_Sensors

BRANCH lineBits, [Search_For_Opponent, Spin_Left, Spin_Right, About_Face]

Read_Line_Sensors: HIGH LLineSnsIn HIGH RLineSnsIn PAUSE 10 RCTIME LLineSnsIn, 1, leftSense RCTIME RLineSnsIn, 1, rightSense ' convert readings to bits lineBits = %00 LOOKDOWN leftSense, >=[blackThresh, 0], lineLeft LOOKDOWN rightSense, >=[blackThresh, 0], lineRight RETURN

A Bit More ComplicatedSearch_For_Opponent: GOSUB Read_IR_Sensors ' If opponent is not in view, scan last known direction. Turn

toward ' opponent if seen by one "eye" -- if both, lunge forward BRANCH irBits, [Scan, Follow_Right, Follow_Left, Lunge]

Scan: BRANCH lastIR, [Move_Fwd, Scan_Right, Scan_Left]

Lunge: ' locked on -- go get him! FOR pulses = 1 TO 15 PULSOUT LMotor, LFwdFast PULSOUT RMotor, RFwdFast GOSUB Read_Line_Sensors IF (lineBits = %11) THEN Match_Over

' in sight and we're on the line NEXT GOTO Main