ROTORFLIGHT - Guide to Blackbox PID Trace Analysis

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Visual Identifiers:

• At the end of a pirouette, the tail comes to a lazy stop (need to increase P-term).
• At the end of a pirouette, the tail comes to a slow, lazy stop (need to increase P-term).
• At the end of a pirouette, the tail bounces several times (need to adjust the D-term → try both higher & lower values).
• At the end of a pirouette, the tail bounces once (try adjusting the feed forward).
• The tail lazily starts the pirouette from the moment you issue a hard abrupt rudder command (need to increase P-term).
• The tail lets go when doing hard pitch-pumps or tictocs (need to increase I-term).
• The tail is oscillating at hover (need to decrease P-term).

Goals of your PID tune:

• Find P-term/D-term balance that makes the tail responsive to your inputs while locking in the arrest when you stop while avoiding 'bounce back' (post rotation).
• Not rely on RotorFlight's "CW Yaw Stop Gain" or "CCW Yaw Stop Gain" settings (this may be a band-aid?).
• No oscillations in tail while hovering or after a pirouette manuever.
• Hard stop when stops pirouetting.
• Visually, your expectation should be that once you start a rudder command, that the tail should follow quickly and as synchronized as much as possible to your stick movements.
• Conversely, when you abruptly release the rudder stick, the tail should stop immediately and with authority, and without a bounce.
• Audibly, you will hear your tail blades thrusting air on a hard stop. They will also generate a "wavering" sound if they are oscillating.

The PID Tuning Plan:

1. Finding the P:D ratio.
2. Increase I-Term until it feels, "Locked In".
3. Adjust the Feed Forward.
4. Refine and increase the P:D ratio.

Procedure:

• In Rotorflight → Profiles → Profile 2: Increase P-Term by +10 per profile like so (Example uses value of "50"):
  • Profile 1: P-Term (P) = 50
  • Profile 2: P-Term (P) = 60
  • Profile 3: P-Term (P) = 70
• Assign a 3-6 position switch to switch through the profiles above midflight to examine the tails behavior.
• Spool up, switch to "idle-1", and maintain a hover @ 5ft AGL.
• Snap the rudder stick to full left pirouetting 360 degrees and immediately stop.
• Fall back into your original hover position if you have drifted away from it.
• Flip the "Profile" switch to the next profile and repeat above steps.
  NOTE: if you notice any severe oscillations, put the switch back to the previous profile/position
• Land, plug-in RotorFlight, D/L the Blackbox logs (and clear/delete) and view in Explorer.

• P=50 (Manuf value)
  
• I=50 (Manuf value)
  
• D=10 (Manuf value)
  
• F=0 (Manuf Value)
  

• Felt "mushy" at 1st.
• There was a bounce back at the "stop" - just once. It was a moderately slow bounce back (not a high frequency/fast type).
• I was expecting D=40 or higher was going to have a substantially positive different feel from this tune but it did not.
• Was expecting oscillations on next value test (D=70).

• P=50 (Manuf default)
• I=50 (Manuf default)
• D=40 (Current view)
• F=0 (Manuf default)

• Feels worst than D=10 (above). I was expecting D=80 might even start to oscillate from being too high.
• The bounce back was getting worst.
• You can see the "PID [yaw]" are starting to react.

• P=50 (Manuf default)
• I=50 (Manuf default)
• D=70 (Current view)
• F=0 (Manuf default)

• After feeling this tune, I realized that the D=40 was not as bad and that the 1st one (D=10) was the best. I retested this and found it was true.
• The bounce back is extreme. Very long/elongated bounce - very lazy bounce too.
• You can see the "PID Error [yaw]" is getting more pronounced (especially when comparing to D=10).

• P=50 (Manuf default)
• I=50 (Manuf default)
• D=15 (Current view)
• F=0 (Manuf default)

• None

• P=50 (Manuf. default)
• I=50 (Manuf. default)
• D=5 (Current view)
• F=0 (Manuf. default)

• None

• P=50 (Manuf. default)
• I=50 (Manuf. default)
• D=0 (Current view)
• F=0 (Manuf. default)

• None

• P=50 (Manuf. default)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=30 (Current view)

• Felt similar but maybe a little worst. Have to check other FF values.

• P=50 (Manuf. default)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=60 (Current view)

• Flight-wise, it was loose and lazy.. worst than before. However, if we review the Blackbox logs, the Feedforward (orange) actually does follow the setpoint a lot closer than all the others.

• P=50 (Manuf. default)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=90 (Current view)

• Felt very loose and lazy of all of them. Going to go back to FF=0.
• Here we see the Feedforward go off the charts.

• P=50 (Current view)
• I=50 (Manuf default)
• D=15 (RCFP selected)
• F=0 (Manuf default)

• TBA

• P=65 (Current view)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=0 (Manuf. default)

• Felt good. Decent stopping power on rudder. Feel like it could be a bit better.

• P=80 (Current view)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=0 (Manuf. default)

• Felt much better. Amazed that it had the stopping power it had even without changing "CW Yaw Stop Gain" or "CCW Yaw Stop Gain".
• Noticing a little high speed oscillation @ hover/stable flight.
• Notice how the "Gyro [yaw]" values are getting closer to the "Setpoint [yaw]" values.

• P=95 (Current view)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=0 (Manuf. default)

• None

• P=110 (Current view)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=0 (Manuf. default)

• Feels the best out of this session. Strongest hold. Quick.. Snappy hold.
• "Gyro [yaw]" in graph slightly out-of-phase from "Setpoint [yaw]" suggests adding "Feed Forward".

• P=120 (Current view)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=0 (Manuf. default)

• Feels very good, strong. Wondering if it's overdriving the servo. Next tune is even higher.
• Note the oscillaton in "PID P [yaw]" while the heli is rotating. This oscillation is causing the "Gyro [yaw]" to dip and oscillate.

• P=130 (Current view)
• I=50 (Manuf. default)
• D=15 (RCFP selected)
• F=0 (Manuf. default)

• Also feels good. Strong. Might be overdriving tail servo. "Gyro [yaw]" shows a single "bounce back tail" (wher P=120 and P=110 does not).

• The testing for Feed Forward values got me thinking that FF may have to be brought up _and_then_ tune for "D". I'll revisit this possibility later.
• P=130 felt the best in terms of overall performance. Stops like a rock! However, there is a little chatter (micro oscillations) associated with it.
• It seems once I hit P=110 (which includes P=120 and P=130) that all of them felt very very similar.
• "PID Error [yaw]" was ever so slightly less than the group of P=110, P=120 and P=130.
• It almost feels worth keeping P=130 and tuning out the "jitters" or "chatter" with D-term.
• As I write this, I have only tuned D for governor, P/D/FF for rudder and OMG the tail already locks so hard even with hard punchouts and not adjusting "I" at all!