Mastering Feed-Forward Tuning for RC Helicopters

Feed-Forward (FF) is a critical, yet often misunderstood, component of modern flight controllers like Rotorflight. While your P-gain handles error correction and your I-term ensures long-term heading hold, Feed-Forward acts as a predictive mechanism. It effectively "tells" the helicopter what the pilot wants to do before the error actually manifests, leading to a more responsive and "locked-in" flight experience.

Unlike PID gains which react to the difference between your stick position and the actual helicopter attitude, Feed-Forward injects a control signal based directly on your stick input. It anticipates the movement, effectively bypassing the delay caused by waiting for an error to develop.

As you observed, increasing Feed-Forward can sometimes lead to a "loose" feel if misconfigured, which seems contradictory to the "locked-in" goal.

• When balanced correctly: FF provides crispness to start and stop maneuvers instantly.
• When too high: It can introduce overshoot, making the heli feel twitchy or causing it to "bounce" upon sudden stick releases.
• The objective: Use FF to achieve the desired response speed, then use PID gains to maintain the final position accuracy.

To tune Feed-Forward effectively, isolate it from your PID loops as much as possible.

1. Baseline PID: Ensure your P-gains and I-terms are already stable and performing well.
2. Small Increments: Increase your FF values in small steps (e.g., 5-10 point increments).
3. The "Stop" Test: Perform rapid, aggressive stops during pirouettes or rolls.
4. Monitor Overshoot: Watch for any tendency of the nose to "rebound" past your intended stop point. If you see this, your FF is likely too high.

Use these specific maneuvers to flesh out whether your current Feed-Forward settings are optimized:

• High-Speed Aggressive Stops: Execute a fast yaw rotation and abruptly return the stick to center. An ideal FF setup will result in a crisp, immediate stop without hesitation or oscillation.
• "Snap" Rolls or Flips: These maneuvers test the predictive capacity of your cyclic and rudder FF. If the heli feels sluggish initiating these, increase FF.
• Rapid Direction Changes: Quickly flicking the sticks from full-left to full-right tests the responsiveness of your flight controller's predictive engine.

Summary Checklist

Note: Always ensure your mechanical linkages are tight and free of slop before making significant changes to FF, as mechanical play can mimic the "bouncy" feel of excessive Feed-Forward.

A Sample Tuning session with Gemini:

When chasing the absolute most "locked-in" feel Rotorflight can offer, Feed-Forward (FF) serves as the primary predictive engine. At a setting of 120, you are sitting in a territory where the flight controller is already injecting a substantial amount of predictive command directly from your stick inputs. Whether 120 is high or low depends entirely on your mechanical setup, servo speed, and blade weight, but it provides a very strong baseline to build upon using your three available banks.

Evaluating 120 FF on Cyclic

A setting of 120 on cyclic means the system is aggressively pushing your servos to match stick velocity.

• If it's too high: You will likely feel a slight "bounce," overshoot, or a loose, disconnected feeling upon quick stick releases.
• If it's too low: The helicopter will feel lazy, mushy, or sluggish on the initial transition of a roll or flip, forcing the P-gain to work harder to catch up.
• The Goal: Maximize FF to the point just before overshoot occurs, letting the PID loop handle precision holding power.

Strategy for Using Your 3 Banks

Since Rotorflight allows you to configure multiple banks, you can use them to safely A/B test different FF values in flight without messing up your proven base tune.

Testing Maneuvers to Differentiate the Banks

To determine which bank gives you the truest "locked-in" feel, fly the same maneuvers across all three banks:

1. Abrupt Stops in Fast Rolls: Initiate a fast roll and snap the stick back to center. Pay close attention to whether the helicopter stops dead on a dime or bounces past your intended stopping point.
2. Rapid Reversals (Pumps / Tick-Tocks): Check the initial "pop" when changing directions. If a bank feels sluggish on the first microsecond of the direction change, its FF is too low.
3. Large Loop / Big Air Carves: Evaluate tracking under high aerodynamic loads to ensure the high FF isn't making the cyclic feel overly twitchy or hyper-sensitive to minor thumb corrections.

Recommendation: Set up Bank 2 and Bank 3 with these tiered adjustments, fly them back-to-back on the same battery, and see which one eliminates any lingering loose sensations while maintaining that crisp start/stop behavior.

Post-test analysis session with Gemini:

Finding that a +/- 10 adjustment across banks 1, 2, and 3 (testing 110, 120, and 130) felt inconclusive indicates that your baseline is already very close to the sweet spot for those specific maneuvers. However, because you skipped high-demand yaw-interactive maneuvers like reversing piro maneuvers, piroflips, and fast tail whips, you missed the exact stress tests that expose the limits of Feed-Forward (FF).

Should You Use Larger Increments?

No, avoid jumping by larger increments (like +/- 20 or 30) for now.

• Cyclic FF is highly sensitive; large jumps can suddenly push your helicopter past the threshold into severe overshoot, making it feel loose, bouncy, or unpredictable.
• A 10-point window is the ideal resolution for fine-tuning a "locked-in" feel. If 110 to 130 felt too similar, it means the delta isn't wide enough *yet* for your current maneuver set, or the maneuvers tested weren't demanding enough on the predictive mixing.

Recommended Action Plan

Instead of changing your gain values immediately, keep your current banks (110, 120, 130) and complete the evaluation using the missing maneuvers:

1. Run the Piro-Set: Take those same three banks through reversing piro maneuvers, piroflips, and fast tail whips.
2. Watch the Axis Interaction: Piroflips and fast piro maneuvers demand rapid, simultaneous mixing of cyclic and collective/rudder. This is where a subtle difference in FF will suddenly become obvious as "crispness" vs "mushiness."
3. Re-evaluate: If the piro-set *still* feels entirely inconclusive across 110, 120, and 130, only then consider expanding your range slightly (e.g., testing 100 on Bank 2 and 140 on Bank 3) to create a more pronounced difference.

Pro-Tip: When you test the piroflips, pay close attention to the entry and exit of the reversal. If the helicopter feels like it's "lagging" behind your sticks as you invert the rotation, your FF is too low. If it kicks or overshoots the stop of a piroflip, your FF is too high.