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PID-Internals

IO variables​

gyroADC/8192*2000 = deg/s

gyroADC/4 ~ deg/s

rcCommand - <-500 - 500> nominal, but is scaled with rcRate/100, max +-1250

inclination - in 0.1 degree, roll and pitch deviation from horizontal position max_angle_inclination - in 0.1 degree, default 50 degrees (500)

axisPID - output to mixer, will be added to throttle(<1000-2000>), output range is <minthrottle, maxthrottle> (default <1150 - 1850>)

PID controller 0, "MultiWii" (default)​

Leveling term​

error = constrain(2*rcCommand[axis], limit +- max_angle_inclination) - inclination[axis]
Pacc = constrain(P8[PIDLEVEL]/100 * error, limit +- 5 * D8[PIDLEVEL])
Iacc = intergrate(error, limit +-10000) * I8[PIDLEVEL] / 4096

Gyro term​

Pgyro = rcCommand[axis];
error = rcCommand[axis] * 10 * 8 / pidProfile->P8[axis] - gyroADC[axis] / 4; (conversion so that error is in deg/s ?)
Igyro = integrate(error, limit +-16000) / 10 / 8  * I8[axis] / 100 (conversion back to mixer units ?)

reset I term if

  • axis rotation rate > +-64deg/s
  • axis is YAW and rcCommand>+-100
Mode dependent mix(yaw is always from gyro)​
  • HORIZON - proportionally according to max deflection
  deflection = MAX(ABS(rcCommand[PITCH]), ABS(rcCommand[ROLL])) / 500 ; limit to 0.0 .. 1.0
  P = Pacc * (1-deflection) + Pgyro * deflection
  I = Iacc * (1-deflection) + Igyro * deflection
  • gyro
  P = Pgyro
  I = Igyro
  • ANGLE
  P = Pacc
  I = Iacc

Gyro stabilization​

P -=  gyroADC[axis] / 4 * dynP8 / 10 / 8
D = -mean(diff(gyroADC[axis] / 4), over 3 samples) * 3 * dynD8 / 32
[equivalent to :]
D = - (gyroADC[axis]/4 - (<3 loops old>gyroADC[axis]/4)) * dynD8 / 32

This can be seen as sum of

  • PI controller (handles rcCommand, HORIZON/ANGLE); Igyro is only output based on gyroADC
  • PD controller(parameters dynP8/dynD8) with zero setpoint acting on gyroADC