ADVANCEDEV3PROGRAMMINGLESSON

UsingtheGyroSensorandDealingwithDrift

BySanjayandArvindSeshan

1. LearnwhattheGyroSensordoes

2. Learnabout2commonproblemswithusingthegyrosensor(driftandlag)

3. Learnwhat“drift”means

4. Learnhowtocorrectfordriftwithagyro“calibration”technique

5. Understandwhyitisimportanttoconsidermultiplesolutionstoaproblemsuchasgyrodrift

Prerequisites:Datawires,Loops,Logic&ComparisonBlocks

Update:Please read the“Gyro SensorRevisited”lesson forimportantupdates (8/6/2017)after you completethis lesson.

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LessonObjectives

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ì Gyrosensordetectsrotationalmotion

ì Thesensormeasurestherateofrotationindegreespersecond(rate)

ì Italsokeepstrackofthetotalrotationalangleandthereforeletsyoumeasurehowfaryourrobothasturned(angle)

ì Theaccuracyofthesensoris±3degreesfor90degreeturn

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WhatistheGyroSensor?

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ì Thereare2commonGyroissues– driftandlagì Drift– readingskeepchangingevenwhentherobotisstillì Lag– readingsaredelayed

ì Inthislesson,wefocusonthefirstproblem:drift.ì WewillcoverlagintheGyroTurnlesson

ì Solutiontodrift:gyrocalibrationì Thesourceofthedriftproblemisthatthegyromust“learn”whatis

still.ì Foracolorsensor,youhaveto“teach”therobotwhatisblackand

whiteì Foryourgyro,youneedtocalibratethesensortounderstandwhatis

“still”

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GyroSensorProblems

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• Thegyroauto-calibrateswhentherobotisturnedonorthegyrowireisconnected.Iftherobotismovingduringcalibration,thegyro“learns”thewrongvaluefor“still”– thiscausesdrift!

• Unfortunately,thereisnogyrocalibrationblock.Thereafewwaystomakethesensorrecalibrate.

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GyroCalibrationtoSolveProblem1:Lag

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• Thebelowarecriticalnotesforusingthegyrocorrectly!!!!!

• THEROBOTMUSTBESTILLWHENYOURUNANYOFTHESECALIBRATIONPROGRAMS!!!!

• JUSTLIKETHECOLORCALIBRATION,YOUSHOULDN’TRUNTHISEVERYTIMEYOUNEEDTOREADTHEGYRO.YOUSHOULDCALIBRATEINASEPARATEPROGRAMJUSTBEFOREYOURUNYOURPROGRAMORONCEATTHEBEGINNINGOFYOURPROGRAM.

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IMPORTANTNOTES

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Calibration:Strategy1

Thegyrorecalibrateswhenitswitchesmodes.So,a“rate”readingfollowedbyan“angle”readingcalibratesthegyro.

Second,addawaitblocktogivethesensorabitoftimetofullyreset.Ourmeasurementsshowthat0.1secondsissufficient.

Notethatintherestofyourprogram,youshouldonlyusethe“angle”modesofthegyro.Usingthe“rate”or“rateandangle”modewillcausethegyrotorecalibrate.

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Calibration:Strategy2

Thisversionofthecalibrationleavesthegyroinrate+anglemode.Thisisusefulifyouusetherateoutput.

Thedownsideofthisversionisthatittakeslonger(about3seconds).Also,youcannotusegyroresetanymore!

Notethatintherestofyourprogram,youshouldonlyusethe“rate+angle”modesofthegyro.Usingthe"angle"or“rate”modewillcausethegyrotorecalibrate.Also,***DONOT***usethegyroreset-thisforcesthegyrointoanglemodewhichwillcausealong3secondrecalibration.

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ì Having afixed timewait forthegyro tocalibratemay not always work.

ì Thegyro returns “Not aNumber”(NaN)until it has actually resetandNaNs arenot >,=,or<any number.This is because they arenot numbers

ì Theonlywayyoucanknowwhenitisfullyresetistomakesureyouaregettingbackarealnumber,insteadofaNot-a-Numbervalueì STEP1:Recalibratethegyroì STEP2:startaloopì STEP3:readangleì STEP4:check angle>=0ì STEP5:check angle<0ì STEP6:ORoutputs ofsteps 4&5ì STEP7:If theoutputofstep 6is true,exitloop

ì Atthis point,thesensor drift should begone.

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Strategy3:Pseudocode

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Strategy3Solution

Notethatintherestofyourprogram,youshouldonlyusethe“angle”modesofthegyro.Usingthe“rate”or“rateandangle”modewillcausethegyrotorecalibrate.

Thisversionofthecalibrationleavesthegyroinanglemode.Thisisprobablythemostcommonwaytousethegyro.Thiscodetakesabout0.1sectorun.

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Strategy4Solution

Notethatintherestofyourprogram,youshouldonlyusethe“rate+angle”modesofthegyro.Usingthe"angle"or“rate”modewillcausethegyrotorecalibrate.Also,***DONOT***usethegyroreset-thisforcesthegyrointoanglemodewhichwillcausealong3secondrecalibration.

Thisversionofthecalibrationleavesthegyroinrate+anglemode.Thisisusefulifyouusetherateoutput.

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DiscussionGuide

1. What are2commonproblems when programming withthegyro?Ans.Gryo drift andGyro lag

2. What does Gyro drift mean?Ans.TheGyro readings keep changing even when therobotis still

3. Canyou move your robotwhen you calibrateyour gyro?Ans.No!!Keep therobotstill.

4. Doyou need tocalibrateyour gryo before every move?Ans.No.Oncebefore you run your entire program

5. Why might it beimportant toconsider multiplesolutions toaproblem?Ans.Inrobotics,there aremultiplewaystosolveaproblem andthere might betradeoffs between thesolutions (e.g.how longthecodetakes torun thecode,canyou useboth rateandanglereadings?)

Update:Please read the“Gyro SensorRevisited”lesson forimportant updates (8/6/2017)

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ì ThistutorialwaswrittenbySanjaySeshan andArvindSeshanandusescodesharedbyHoosierGirlz(http://www.fllhoosiergirlz.com)

ì Morelessonsatwww.ev3lessons.com

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Credits

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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