5" freestyle: PID retune after frame swap

The previous frame had developed a hairline crack in one of the arm standoffs — visible when flexing, not visible at rest. I’d been getting mid-throttle oscillations for two sessions and initially blamed the tune. It was the frame.

New frame is 4mm arm carbon vs. 3mm on the old one. Stiffer, heavier by 18g. The PIDs from before were useless.

Starting point: Betaflight’s built-in auto-tune. Let it run three battery packs. The result was overtuned for freestyle but gave me a baseline for the noise floor.

# Betaflight 4.5 — post-autotune starting values
set p_pitch = 52
set i_pitch = 62
set d_pitch = 38
set f_pitch = 140

set p_roll = 50
set i_roll = 60
set d_roll = 36
set f_roll = 135

From there, I reduced D on both axes by 6 points (noise on the blackbox trace was low, didn’t need the damping), bumped F up to 160 to get sharper stick response, and dropped master multiplier from 1.0 to 0.85. The result feels cleaner than the old frame ever did.

Two sessions in, no oscillations. Blackbox shows a tidy step response. I’ll leave it here unless something changes.

The lesson from the crack: check arm flex on any crash that lands arm-first. A cracked arm will tune-hunt you for weeks before it shows itself.