Identifying Blackbox Trace Behavior

D-Term Tuning Trace Identification:

Condition Description Trace Behavior
D-term too high The D-term is overly dampening the response, causing excessive correction and oscillations. - The Gyro [axis] trace will show high-frequency oscillations as the D-term overreacts to small changes.
- The PID D [axis] trace will have sharp oscillations or spikes.
- The craft may feel "twitchy" or jittery in flight, especially after sharp inputs.
D-term too low The D-term isn't adequately smoothing out rapid changes, leading to instability. - The Gyro [axis] trace will overshoot the Setpoint [axis], and the system may feel loose or underdamped.
- The PID D [axis] trace will have minimal correction, often remaining flat during fast maneuvers.
Oscillations in D-term Oscillations in the D-term indicate that the D-term value is too high. - You'll see excessive oscillations in the PID D [axis] trace as it tries to overcompensate.
- The Gyro [axis] trace may also reflect these oscillations, especially after aggressive inputs.
D-term interacting with P-term When the P-term is high, the D-term may try to overcorrect, leading to additional oscillations. - You'll see the PID D [axis] trace spike as it works to smooth out the aggressive P-term corrections.
- Gyro [axis] may have small oscillations, showing that D-term is compensating too aggressively.
D-term behavior during snap maneuvers During a snap maneuver, the D-term should help prevent overshoot and control bounce-back. - After a snap input, the Gyro [axis] may briefly overshoot the Setpoint [axis], but the D-term should quickly correct the motion.
- Watch for bounce-back after the snap; if it's too strong, the D-term may need adjustment.

P-Term Tuning Trace Identification:

Condition Description Trace Behavior
P-term too high The system is overly aggressive in correcting errors, causing oscillations. - The Gyro [axis] trace will oscillate excessively around the Setpoint [axis].
- You'll see quick oscillations of the Gyro [axis] as the P-term overcorrects.
- The first leg of the Gyro [axis] trace will follow the Setpoint [axis] more closely.
- This behavior is often seen in sharp peaks and valleys in the gyro signal.
P-term too low The system responds sluggishly to errors, leading to a slow correction. - The Gyro [axis] trace will lag behind the Setpoint [axis], indicating under-correction.
- The response will appear more smoothed out but with larger deviations from the setpoint.
- The craft may feel "loose" or slow to respond in flight.
P-term oscillations Oscillations in the P-term indicate excessive or aggressive corrections. - The Gyro [axis] trace will show repeated oscillations around the Setpoint [axis].
- PID P [axis] will also reflect these high-frequency oscillations.
- You may see more pronounced oscillations after quick control inputs.
P-term and D-term interaction When the P-term is high, the D-term may overcompensate by trying to smooth out the response, leading to oscillations. - PID D [axis] will show high-frequency oscillations as the D-term reacts to aggressive P-term corrections.
- Gyro [axis] may exhibit small, quick oscillations or appear jittery around the Setpoint [axis].

I-Term Tuning Trace Identification:

Condition Description Trace Behavior
I-term too high The I-term builds up too much over time, leading to slow oscillations and a delayed response to long-term errors. - You'll see slow oscillations in the Gyro [axis] trace, even when the setpoint is constant.
- The PID I [axis] trace will grow larger and then slowly decay, indicating excessive I-term accumulation.
I-term too low Long-term errors (such as drift) are not corrected effectively. - The Gyro [axis] will gradually drift away from the Setpoint [axis] without returning.
- The PID I [axis] trace will remain relatively flat or small, indicating a weak correction over time.
I-term oscillations Oscillations in the I-term reflect overaccumulation of error, often leading to sluggish corrections. - Slow oscillations can be seen in the Gyro [axis] trace as the I-term overcorrects for accumulated error.
- PID I [axis] will have long, undulating waves as it tries to overcorrect.
- This is more apparent in situations where the craft holds a constant attitude for a longer time.
I-term and D-term interaction Overdamping or slow response caused by a high D-term suppressing the I-term's ability to correct long-term errors. - You may notice the Gyro [axis] trace lagging after quick changes but stabilizing very slowly.
- PID D [axis] and PID I [axis] traces might appear to conflict, with the D-term suppressing small adjustments from the I-term.
I-term and P-term interaction When the P-term is too high or low, the I-term may struggle to correct drift or accumulate too much error over time. - If P-term is too high, PID I [axis] might accumulate more error, resulting in slow oscillations.
- If P-term is too low, PID I [axis] will have to compensate more, causing the Gyro [axis] to drift more significantly before it stabilizes.

Integrated Guidelines:

  • I-term too high: Can dampen the affects of P-term changes. So for example if you run a high I-Term of say "120" and try to run profiles showing the differences between P=60, P=80, P=100 - then the traces may not noticeably differ.
  • Feed Forward too high: Can dampen the affects of P-term changes. So for example if you run a high Feed Forward of say "80" and try to run profiles showing the differences between P=60, P=80, P=100 - then the traces may not noticeably differ.
  • D-term too high: You originally pointed out that oscillations in the PID D [axis] trace are a sign of the D-term being too high. This is a good indicator that over-damping is occurring, which causes unwanted oscillations.
  • D-term too low: If the Gyro [axis] overshoots the Setpoint [axis] frequently, the D-term is likely too low, which means the system is not dampening the corrections sufficiently.
  • D-term interaction with P-term: An essential guideline here is how the D-term works to smooth out aggressive P-term corrections. This relationship can lead to additional oscillations if not tuned correctly.
  • D-term behavior during snap maneuvers: A critical moment to observe D-term performance is during rapid input changes like snap maneuvers, where bounce-back can indicate insufficient D damping.
  • P-term(low)/D-term(high): Get high PID Error [axis], I-term accumulates (assists the P-term). This is an I-term induced bounce-back.
  • P-term(high)/D-term(low): Overshoot of Setpoint [axis] (sometimes constant overshooting - as in an oscillation). You will hear an audible "trill" and can be seen in t he 'PID Sum [axis]' trace.
  • Feed Forward too low: P-term/D-term have proper ratio but "Gyro [axis]" is lagging (out-of-phase) from "Setpoint [axis]"

Visual Examples:

  • P-Term too low seen in "Gyro [yaw]" (light purple trace) lagging (not following the shape of Setpoint) from "Setpoint [yaw]" (light yellow trace):


  • D-Term too high causing oscillations (left). D-Term adjusted (lowered) to reduce oscillations (right):


  • More image examples to come later..