Lab8:Self-balancingSegway ImperialCollegeLondon

V1.0-PYKCheung,14March2018 Lab8- 1

DysonSchoolofDesignEngineering

ImperialCollegeLondon

DE2.3Electronics2

LabExperiment8:PuttingEverythingTogether

(webpage:http://www.ee.ic.ac.uk/pcheung/teaching/DE2_EE/)

INTRODUCTION

ThislabinstructionisintendedtohelpyoutoputeverythingthatyouhavelearnedtogethertocompletetheTeamproject.Itcontainsvarioustipsandguidelines,snippetsofPythoncode,pseudo-codeofthetop-levelprogram,relatedtothedifferenttasksthatyourteamisexpectedtoachieve.

TIPS1:FROMIDLETORUNNING

RunninganembeddedprogrammeonthePyBenchboardcancauseproblembecauseassoonasyoupresstheRESETbutton,youusuallystarttheprogramme(whichprogrammeyourundependsontheDIPswitchsetting).ItisoftenhelpfuliftheSegwayisinanidlemode,andonlyrunyourprogrammewhenyoupresstheUSERbutton.

HereweusetheOLEDdisplaytotelluswhattheSegwayisdoing.RememberthatdrawinganythingontheOLEDisVERYSLOW.Therefore,onlydothatoutsidethemainprogramloop.Wealsoincludetheprintstatementstohelpdebugging.ThesewillshowuponthePuttyortheTerminalwindowonyourlaptop.

TIPS2:MODIFYTHEMAIN.PYFILE

Sofar,thewayIhaveorganizedthePybenchsystemontheSegwayistorunPybenchdriverpybench_main.py,withtheDIPswitchesaresetto00,runaself-testprogramifSW=01or10,andfinallyrunuser.pyifSW=11.Tomakethingseasierfortheteamproject,Irecommendthatyoumodifytheprogrammain.pysothatyourunthevariousmilestonesdependingontheDIPswitchsettingasshownbelow.

Lab8:Self-balancingSegway ImperialCollegeLondon

V1.0-PYKCheung,14March2018 Lab8- 2

TIPS3:PSEUDO-CODEFORMILESTONE3

I assume that by now, you should have completedmilestones 1 and 2. Formilestone 3, your goal is to useyour improved beat-detection routine to synchronousmusicwith dancingmoveswith the stabilizer (i.e. no self-balancing). You should store thedancemove ina text file(ASCIIformat),readthisfileatthestartoftheprogramandstorethemovesinanarrayBEFOREthemainprogramloop.This is because readingASCII characters froma text file isvery slow. It is farbetter to store information inmemory(i.e.anarray)andaccessthisarrayinsidetheprogramloop.

Furthermore,ifyouhavenotlearnedPythonKeywordsTryand Finally, you should. Here is the pseudo-code forMilestone3.

TIPS4:PITCHANGLEESTIMATION

BynowyoushouldbefamiliarwithusingtheIMUtoestimatethepitchangleusingComplementaryFilter.Hereisafunctionthatestimatethepitchangle,justtohelpyoualongabitquicker.dtisdeltatime,thetime since the last reading in the program loop. You finddtwith tic andpyb.millis() orpyb.micros().Don’tforgettoadjustdttosecondsinyourequation.

TIPS5:PIDCONTROLLER

ThebasicPIDcontrollerequationisstraigthforward:

IrecommendyoutocreateaPIDcontrollerfunction(orifyouaregoodinPythoncoding,createaclass)thatdothefollowing:

Inputtofunction:pitchangle,(rateofchangeofpitch(pitch_dot),target(orset-point),cumulativepitcherror(integralterm).

Outputofthefunction:PWMdrivevaluelimitedto±100.

Youshouldalsolimittheset-pointtoasmallvalue,suchas±3degrees(say).

Finally,youwillfindthattheIMUmayNOTreturnapitchangleofzerowhenitisupright.ThisisbecausethecentreofgravityoftheSegwaymaynotbedeadcentre.Thisdependsonthepositionofthebatteryandotherfactors.Youthereforemayneedtotakethisintoaccount.

𝑤(𝑡) = 𝐾(𝑒(𝑡) + 𝐾+�̇�(𝑡) + 𝐾- . 𝑒(𝜏)𝑑𝜏

Lab8:Self-balancingSegway ImperialCollegeLondon

V1.0-PYKCheung,14March2018 Lab8- 3

Thepseudo-codeforthecontrollerfunctionis:

TIPS6:TUNINGTHEPIDCONTROLLER

Finally, youwould need to tune the PID controller. Oneway to do this is tomodify the programandchangethethreegainvalues:Kp,KiandKdinthePythoncode.Amuchbetterwaytodothis(thankstoBen Greenberg last year) is the use the potentiometer on the Pybench board together with the USRswitchtoadjustthesegainvalueslive!Hereisthecodetodothat:

Onceyouhave tuned thePIDcontroller, youcan replace thepot.read() statementwith the tunedgainvalue.Thentostarttheprogram,youjustpresstheUSRswitchfewtimesandtheself-balancingprogramwillrun.

Lab8:Self-balancingSegway ImperialCollegeLondon

V1.0-PYKCheung,14March2018 Lab8- 4

TIPS7:PSEUDO-CODEFORSELF-BALANCING,DANCINGSEGWAY

Nowputallthesetogether,hereisthepseudo-codeofapossiblefinalprogramtodobothself-balancinganddancingtomusic:

Notethat thisprogram loophas twotimescales: thecontrolleruses tic1, inmicroseconds. Thepollingloopchecksfor5msecelapsetime.Thismeansthecontrolloopisrunningatround200Hz.

Thebeatdetectionusestic2inmilliseconds.Theloopisdetectingbeatsatmuchlowerfrequency.