labview™ for lego® mindstorms - tetrix® robotics
TRANSCRIPT
159
Harvester and Transporter Programming Guide (LabVIEW™ for LEGO® MINDSTORMS®)
Introduction:
Inthisguide,theRangerBotwillbeprogrammedtofollowaline,pickupanobjectusingtheharvester,andputtheobjectintothetransporter.Itwillalsocountthenumberofobjectscollected.ThisguideisforusewiththeLabVIEW™forLEGO®MINDSTORMS®programminglanguage.
Review:
•To reviewthebasicprinciplesofconnectingtotheNXTBrickandconfiguringLabVIEWforLEGOMINDSTORMSforusewithvarioussensorsandmotors,reviewtheProgrammingGuidesandTutorialVideosfromLessons2and3.
•ToreviewthebasicprinciplesofprogramminginLabVIEWforLEGOMINDSTORMS,reviewtheProgrammingGuidesandTutorialVideosfromtheLineFollowerProgrammingExtension.
•ThesematerialscontaindetailedinformationabouthowtousetheSchematicEditor,andhowtocreatethestructures,functions,constants,andwiresthatarepresentedinthisguide.
•ThisprogrammakesuseoftheScreen Update SubVI,providedontheTETRIX® Getting Started GuideDVD.ThisfunctionusestheNXTtodisplaycustomtextaswellaslightandultrasonicsensorreadings.
•Usethesestepstoaddthefunctiontotheprogram:
a.Withintheblockdiagram,right-clicktobringuptheFunctionspaletteandchooseSelect a VI.
b.ThennavigatetowheretheScreen Update SubVIissaved.
Note:IftheScreenUpdateSubVIhasnotbeensavedonthecomputerinaspecificlocationalready,downloaditfromtheDVDbynavigatingtotheResourcestabandselectingtheScreen Update SubVI Program (LabVIEW for LEGO MINDSTORMS)button.
c.OncetheScreenUpdateSubVIhasbeenlocated,openitandplaceitontheblockdiagram.
Getting Started:
1.Openanewprojectfileandgototheblockdiagram.
a.CreateanewRangerrobotprojectandnameitHarvester and Transporter.
b.UsingtheSchematicEditor,configuretherobottohaveaTETRIX180°ServoMotorattachedtoServoPort1.
c.CreateanewVI.
TETRIX®GettingStartedGuideExtensions
160
Initialize the Servo:
2.Thecodeinvolvesfirstinitializingtheservoposition,delayingforonesecond,andthenenteringthemaincodeWhileLoop.
a.Createthecodeshown,beginningwiththeMove Servos function,thenthe Wait for Time (sec)function.
b.NotethatthereisalargeWhileLoopenclosingtheremainderofthecode.CreatethisWhile Loopandensureitiswideenoughtocontainallthecodethatfollows.
Line Follower Code:
3.InsidetheWhileLoop,thecodedisplaysthecurrentballcountandthenperformsaline-followingfunctionwithaspeedthatvariesbasedontheproximitytotheultrasonicsensor.
a.Createthecodeshown,beginningwiththeScreen Update SubVI,thentheRead Touch (Count)functionandthentheDraw NumberfunctiontodisplaythecurrentballcountontotheNXTBrickdisplay.
b.Next,theultrasonicsensoriscomparedtoathresholdtodeterminethemotorspeedwhichissenttoeithertherightorleftmotor,dependingonwhetherthelightsensorreadingshowsthattherobotisontheline.
Harvester and Transporter Programming Guide (LabVIEW™ for LEGO® MINDSTORMS®)
ExtensionsTETRIX®GettingStartedGuide
161
Harvester and Transporter Programming Guide (LabVIEW™ for LEGO® MINDSTORMS®)
Harvest Ball When Detected Code:
4.Next,theproximitytoanobjectischeckedagain.Iftheobjectisveryclose,thentherobotentersharvestingmodebystopping,raisingtheservotocollectaball,andwaitingforaballtoenterthetransporter.
a.Createthecodeshown,beginningwiththethresholdcomparisonandtheCase structure.Then,usethe Align Text Centerfunctiontowrite“Found!”totheNXTdisplay,theMotor Move command,andtheWait for Time (sec)function.
b.Next,aForLoopisusedtoraisetheservofrom150to30unitsinstepsof1witha10-milliseconddelaybetweensteps.
Note:A +1(increment) functionisusedbecausethevalueoftheindexterminalstartsatzero.
c.Next,the Read Touch (count)functionisplacedinsidea While Loop,readingcontinuouslyuntiltheballcounthasincreasedovertheinitialreadingatthestartoftheWhileLoop.
5.Oncetheballcounthasincreased,therobotpauses,backsup,andthenlowersitsarm.
a.Createthecodeshown,beginningwiththeWait for Time (sec)function,followedbytheMove Motorsfunction,anotherWaitforTime(sec),andthenaMoveMotorstostopthemotors.
b.Next,aFor Loop isusedtolowertheservobackdownfrom30to150units,instepsof1witha10-milliseconddelaybetweensteps.
Note:A+1(increment)functionisusedbecausethevalueoftheindexterminalstartsatzero.
c.Then,aone-seconddelayexecutesbeforethelooprepeats.
TETRIX®GettingStartedGuideExtensions
162
Harvester and Transporter Programming Guide (LabVIEW™ for LEGO® MINDSTORMS®)
d.Noticethe Read NXT ButtonsfunctionwiredtotheconditionterminaloftheouterWhileLoop.ThisensuresthatthecoderunsuntiltheEnterbuttonoftheNXTispressed.
6.Finally,iftheCase structureconditionisFalse,indicatingthatnoobjectisdetected,thennocodeisexecutedbytheCasestructure,andtherobotwillcontinueitsline-followingbehavior.
ExtensionsTETRIX®GettingStartedGuide