getting wrong gains for dc motor pid

[PrathamMeena]

Hi, I'm using the autotune PID library for finding the gains of the dc motors of my differential drive. I am using a teensy 3.2 microcontroller, a sabertooth 2x12 motor driver, HC-05 Bluetooth module, two dc motors, and two external rotary/incremental encoders having 360ppr. I was unable to find any example to use the autotune library except for the library example so I used it as a reference and made the changes to suit my code. Here it is

#include <PID_v1.h> #include <PID_AutoTune_v0.h> #include <SoftwareSerial.h> #include <SabertoothSimplified.h> //library for sabertooth motordriver

SoftwareSerial SWSerial1(0,2); SabertoothSimplified ST1(SWSerial1);

int pinA1 = 11; int pinB1 = 12; int pinA2 = 7; int pinB2 = 8; int count1 = 0, count2 = 0; // encoder counts int prevCount1=0, prevCount2 = 0; // last count unsigned long prevTime1=0,prevTime2=0,prevTime3=0,prevTime4=0,prevTime5=0; double reqRPM1 = 150,reqRPM2 = 150,reqTheta = 0 ; // required RPM double actRPM1 =0,actRPM2= 0,motorInput2=0; // actual RPM byte ATuneModeRemember=2; double kp=0.43793,ki=0.06332,kd=0.75718; // parameters obtained from autotuner double aTuneStep=45, aTuneNoise=10, aTuneStartValue=55; unsigned int aTuneLookBack=1; unsigned long modelTime, serialTime; double kpmodel=1.5, taup=100, theta[50]; double outputStart=5; boolean tuning = false; //changed to false after tuning

PID myPID(&actRPM2, &motorInput2, &reqRPM2,kp,ki,kd, DIRECT); PID_ATune aTune(&actRPM2, &motorInput2);

boolean useSimulation = true; //set to false to connect to the real world

void Check2() // interrupt function to get encoder readings { if(digitalRead(pinB2) == digitalRead(pinA2)) count2--; else count2++; }

void setup() { myPID.SetMode(AUTOMATIC); aTune.SetControlType(1); ST1.motor(1,0); // running only one motor for now delay(1000);

// if(tuning) //commented this code otherwise the autotuner was not starting // { // tuning=false; // changeAutoTune(); //this functions sets output to atuneStartValue and was not letting //autotuner to start, had to comment this for it to run // tuning=true; // }

serialTime = 0; if(useSimulation) { for(byte i=0;i<50;i++) { theta[i]=outputStart; } modelTime = 0; } //encoder pins pinMode(pinA2,INPUT); pinMode(pinB2,INPUT); //interrupt attachInterrupt(digitalPinToInterrupt(pinA2),Check2,RISING); //keeping track of time from start prevTime1 = micros(); prevTime4 = micros(); prevTime5 = micros();

Serial.begin(9600); SWSerial1.begin(9600);//serial for sabertooth motor driver }

void loop() { unsigned long now = micros(); ST1.motor(1,0); // running only one motor

if((micros()-prevTime1)>10000) // run every 10 ms { if(tuning) { byte val = (aTune.Runtime()); if (val!=0) { tuning = false; } if(!tuning) { //we're done, set the tuning parameters kp = aTune.GetKp(); ki = aTune.GetKi(); kd = aTune.GetKd(); myPID.SetTunings(kp,ki,kd); AutoTuneHelper(false); } } else { myPID.Compute(); }

if(useSimulation) { theta[30]=motorInput2; if(now>=modelTime) { modelTime +=100; actRPM2 = getRPM2(); // instead of DoModel() in order to update input value I placed my // code to update input in this portion ST1.motor(2 ,motorInput2); // sending values to motor } }

if(micros()>serialTime) { SerialReceive(); SerialSend(); serialTime+=500; } prevTime1 = micros(); } }

int getRPM2() // calculating RPM { long pps2 = long(count2 - prevCount2); float ppr2 = 360; prevTime4 = micros() - prevTime5; double tt = prevTime4 / 6000.0 ; double actRPM2 = ((pps2*10000.0)/(tt*ppr2)); prevTime5 = micros(); // SWSerial2.print(" rpm2= " ); // SWSerial2.println(actRPM2); prevCount2 = count2; return actRPM2; }

void changeAutoTune() { if(!tuning) { //Set the output to the desired starting frequency. //removed one line of code that sets the output to aTuneStartValue aTune.SetNoiseBand(aTuneNoise); aTune.SetOutputStep(aTuneStep); aTune.SetLookbackSec((int)aTuneLookBack); AutoTuneHelper(true); tuning = true; } else { //cancel autotune aTune.Cancel(); tuning = false; AutoTuneHelper(false); Serial.print("Adad222"); } }

void AutoTuneHelper(boolean start) { if(start) ATuneModeRemember = myPID.GetMode(); else myPID.SetMode(ATuneModeRemember); }

void SerialSend() { Serial.print("setpoint: ");Serial.print(reqRPM2); Serial.print(" "); Serial.print("input: ");Serial.print(actRPM2); Serial.print(" "); Serial.print("output: ");Serial.print(motorInput2); Serial.print(" "); if(tuning){ Serial.println("tuning mode"); } else { Serial.print("kp: ");Serial.print(myPID.GetKp(),5);Serial.print(" "); Serial.print("ki: ");Serial.print(myPID.GetKi(),5);Serial.print(" "); Serial.print("kd: ");Serial.print(myPID.GetKd(),5);Serial.println(); } }

void SerialReceive() { if(Serial.available()) { char b = Serial.read(); Serial.flush(); if((b=='1' && !tuning) || (b!='1' && tuning))changeAutoTune(); } }

Even after I commented the changeAutoTune and AutoTuneHelper the autotuner was taking forever to end. So I looked at the library .cpp file and tweaked with LookBackSec, Noise, and some other values, getting no success. Finally, when I reduced the value of nLookBack in RunTime function to a value lower than 9 (worked good till 5 for me) the tuner came to an end after oscillating for a while. But the problem is the values that I am getting are too high that it makes the pid unstable.