understanding altitude hold algorithem

This forum is dedicated to software development related to MultiWii.
It is not the right place to submit a setup problem.
Software download

understanding altitude hold algorithem

Postby Jazon » Sat Jan 07, 2017 7:15 pm

Hi there, i want to understnd the algorithem of altitude hold of multiwii 2.4.

this part of code is for altitude hold
Code: Select all
#if BARO
uint8_t getEstimatedAltitude(){
  int32_t  BaroAlt;
  static float baroGroundTemperatureScale,logBaroGroundPressureSum;
  static float vel = 0.0f;
  static uint16_t previousT;
  uint16_t currentT = micros();
  uint16_t dTime;

  dTime = currentT - previousT;
  if (dTime < UPDATE_INTERVAL) return 0;
  previousT = currentT;

  if(calibratingB > 0) {
    logBaroGroundPressureSum = log(baroPressureSum);
    baroGroundTemperatureScale = ((int32_t)baroTemperature + 27315) * (2 * 29.271267f); // 2 *  is included here => no need for * 2  on BaroAlt in additional LPF
    calibratingB--;
  }

  // baroGroundPressureSum is not supposed to be 0 here
  // see: https://code.google.com/p/ardupilot-mega/source/browse/libraries/AP_Baro/AP_Baro.cpp
  BaroAlt = ( logBaroGroundPressureSum - log(baroPressureSum) ) * baroGroundTemperatureScale;
 
  alt.EstAlt = (alt.EstAlt * 6 + BaroAlt ) >> 3; // additional LPF to reduce baro noise (faster by 30 µs)
  #if (defined(VARIOMETER) && (VARIOMETER != 2)) || !defined(SUPPRESS_BARO_ALTHOLD)
    //P
    int16_t error16 = constrain(AltHold - alt.EstAlt, -300, 300);
    applyDeadband(error16, 10); //remove small P parametr to reduce noise near zero position
    BaroPID = constrain((conf.pid[PIDALT].P8 * error16 >>7), -150, +150);

    //I
    errorAltitudeI += conf.pid[PIDALT].I8 * error16 >>6;
    errorAltitudeI = constrain(errorAltitudeI,-30000,30000);
    BaroPID += errorAltitudeI>>9; //I in range +/-60
 
    applyDeadband(accZ, ACC_Z_DEADBAND);

    static int32_t lastBaroAlt;
    // could only overflow with a difference of 320m, which is highly improbable here
    int16_t baroVel = mul((alt.EstAlt - lastBaroAlt) , (1000000 / UPDATE_INTERVAL));

    lastBaroAlt = alt.EstAlt;

    baroVel = constrain(baroVel, -300, 300); // constrain baro velocity +/- 300cm/s
    applyDeadband(baroVel, 10); // to reduce noise near zero

    // Integrator - velocity, cm/sec
    vel += accZ * ACC_VelScale * dTime;

    // apply Complimentary Filter to keep the calculated velocity based on baro velocity (i.e. near real velocity).
    // By using CF it's possible to correct the drift of integrated accZ (velocity) without loosing the phase, i.e without delay
    vel = vel * 0.985f + baroVel * 0.015f;

    //D
    alt.vario = vel;
    applyDeadband(alt.vario, 5);
    BaroPID -= constrain(conf.pid[PIDALT].D8 * alt.vario >>4, -150, 150);
  #endif
  return 1;
}



so there is 2 PID .
the first ther is only P and I. the output will feed the seconde PID, which based only in D term from velocity and the output will feed motors right.

please can anyone confirm me this
Jazon
 
Posts: 10
Joined: Mon Oct 24, 2016 3:21 pm

Return to Software development

Who is online

Users browsing this forum: No registered users and 3 guests

cron