Overview / Guide PID set-up and Tuning

I am interested in the basics of what each of the 12 PID paramaters actualy controls and the relation of one to another.....

I have read and really have a pretty good grip on PID's, the adjustments and gain factors. 

Servo - roll, pitch, yaw.   Correct me if I'm wrong...PID tuning all coresponds to how the servo responds to where the NAV portion says that it should be.  ie NAV calls for a 45 deg RH bank roll PID is the control of how quickly/precisely a roll is exicuted.

NAV - all has to do with the navigation of the airplane and how navigational changes are made to guide the airplane to its next waypoint. 

That being said here is where my questions come in....Nav Roll - simple enough.  Nav Pitch AS, NAV Pitch Alt - obviously one is airspeed while the other is altitude. 

     1.  How does one corespond with the other?

     2.  Why is it that when I watch my flight log after flying a mission NAV Pitch stays above 0 at all times, the Servo Pitch follows NAV Pitch and my plane continues to climb through the entire mission as well.

     3.  Energy/Alt PID - information needed.

     4.  Other Mix's - P to T...I am guessing Pitch to Throttle?

          Pitch Comp - information needed.

          Rudder Mix - Rudder to Aileron Mix.

     5.  Throttle 0-100%

          Cruise - % of throttle while at Cruise

          Min/Max - self explanatory

          FS Value - Fail Safe Value

     6.  Xtrack Pids - information needed.

          Gain (cm) - is this similar to a "Target Point Distance"?

          Entry Angle - information needed.

     7.  Navigation Angles *100 - seems odd to me that for a 45 deg bank you have to put in 4500 (just a thought, maybe there are bigger reasons to this).

          Bank Max, Pitch Max, Pitch Min - all self explanatory.

     8.  Airspeed m/s

          Cruise * 100 - again, I don't get why it is multiplied by 100???

          FBW Min, FBW Max - self explanitory.

          Ratio - ratio of what to what????

 

I've looked and haven't found a thread anywhere that talks about all of this, if there is a link could someone please send it to me?

 

 

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Replies

  • Maybe this is what you are looking for? 

    http://code.google.com/p/ardupilot-mega/wiki/AdvancedConfig

  • Developer
    1) One is used if you have an airspeed sensor (Nav Pitch AS). The other is used if you don't
    2) You didn't provide enough info to hazard a guess, but you have something set up incorrectly
    3) If you have an airspeed sensor then pitch is used to control airspeed and throttle is used to control altitude. The throttle control loop actually looks at total energy instead of just altitude. It is a subtle but important difference.
    4) P to T, pitch to throttle - not needed for most airframes. Pitch Comp, roll to pitch feedforward - tune so that you don't climb or descend in turns. Rudder mix - Aileron to rudder mix (not the other way around)
    5) Is there a question here?
    6) Cross track gain is the amount to adjust the current heading based on distance of track line. Units are degrees (*100) per meter. Entry angle is a limit to how much cross track correction will be applied.
    7, 8) Jason answered.

    I will (hopefully) do one or more videos on tuning one day for the wiki, but it is quite a big topic. With an assistant, video, and telemetry I would estimate it takes me no less than an hour of flight time to tune a new airframe.
  • Developer

    "I don't get why it is multiplied by 100"

    A lot of the maths in APM use scaled integers to avoid floating point. The config tools are exposing you to that fact, maybe unnecessarily, but that's easier for the developers right now. I'm sure it will evolve over time. Just assume all angles and speeds are * 100, and lat/long is 10x7.

    I have a post on Crosstrack PIDS, with an interactive tool on setting them.

    AS ratio is tuning thing. More to do with getting the most accuracy out of your Pitot setup.

     

     

     

     

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