Summary¶

libdrone uses two Betaflight PID profiles and three rate profiles to cover its operating scenarios. Profile 1 is the standard chase/mapping configuration. Profile 2 is the low-speed EASA A2 compliance configuration, capping effective airspeed to ≤4.8 m/s for urban and skatepark operations. Rate profiles store stick sensitivity settings independently of PID gains — one per prop set. The TX16S switch SC selects between profiles in flight; switching is instant with no reboot required.

Concept¶

PID profiles vs rate profiles¶

Betaflight separates two independently switchable configuration sets:

PID profiles (up to 3) store all PID gains, filter settings, and throttle limiting. Switching profiles changes how aggressively the drone responds and what its maximum speed is. libdrone uses: - Profile 1: standard operation — full speed, standard PID gains - Profile 2: A2 compliance — throttle scale 55%, same PID gains

Rate profiles (up to 3) store stick sensitivity (rates, expo, RC smoothing). They are independent of PID profiles. libdrone uses: - Rate 1: HQ 6×3×3 propeller set (higher pitch — slightly different feel) - Rate 2: HQ 6×2.5×3 propeller set (lower pitch — adjusted for efficiency)

Switching between prop sets requires switching both the physical props and the rate profile. Betaflight does not know which props are installed — the pilot is responsible for matching the rate profile to the prop set.

Low-speed compliance (Profile 2)¶

EASA Open A2 operational category requires that the drone cannot exceed certain speeds in the operating area. Betaflight's THROTTLE_LIMIT_TYPE SCALE with THROTTLE_LIMIT_PERCENT 55 scales the full throttle range down to 55% of its mechanical maximum. The drone can still reach 100% of the throttle range on the sticks, but the actual motor output is capped.

After applying Profile 2, the calibration procedure is: fly a straight line at full stick throttle in calm conditions, check GPS speed in OSD, adjust throttle_limit_percent until peak GPS speed is consistently at or below 4.8 m/s. This value is not universal — it varies with battery state of charge, payload weight, and atmospheric conditions. Calibrate on the day of the operation.

Flight mode switches¶

The TX16S switch assignments:

Reference¶

Profile 2 — low-speed compliance overlay¶

Apply on top of the base configuration. Paste in CLI:

``` profile 2

set throttle_limit_type = SCALE set throttle_limit_percent = 55

save ```

Calibration target: GPS speed ≤ 4.8 m/s at full throttle in Profile 2. Adjust throttle_limit_percent in 5% steps until calibrated.

Rate profile starting values (both prop sets)¶

```

Rate profile 1 — HQ 6×3×3 (higher pitch)¶

rateprofile 1 set roll_rc_rate = 90 set pitch_rc_rate = 90 set yaw_rc_rate = 80 set roll_expo = 15 set pitch_expo = 15 set yaw_expo = 10

Rate profile 2 — HQ 6×2.5×3 (lower pitch)¶

rateprofile 2 set roll_rc_rate = 85 set pitch_rc_rate = 85 set yaw_rc_rate = 80 set roll_expo = 15 set pitch_expo = 15 set yaw_expo = 10 ```

Procedure¶

Switching profiles in flight¶

1. Profile is selected by the SD switch position (Profile 2 = Low Speed).
2. In the air, the switch can be flipped at any time. The new PID profile takes effect immediately — there is no glitch or reboot.
3. Verify the correct profile is active before arming: OSD should show the profile number if configured as an OSD element, or check by briefly going to full throttle and observing whether speed is limited.

Calibrating Profile 2 for the day¶

1. Select Profile 2 (SD switch down).
2. Fly outdoors in calm conditions. Make a straight horizontal pass at full throttle away from the pilot.
3. Note peak GPS speed from OSD or post-flight Blackbox.
4. If peak speed > 4.8 m/s: reduce throttle_limit_percent by 5.
5. If peak speed < 3.5 m/s: increase throttle_limit_percent by 5.
6. Repeat until peak speed is 3.8–4.5 m/s (buffer below 4.8 m/s limit).
7. Save the calibrated value in Profile 2. Document the value with the payload weight used for calibration.

Rationale¶

Why throttle scale rather than speed limiting via GPS¶

Betaflight does not implement GPS-based speed limiting in standard operation — GPS speed feedback would require an outer control loop running at GPS update rate (10 Hz), which is incompatible with the tight PID loop timing. Throttle scale is a simple, reliable, zero-latency mechanical cap that guarantees the motor output cannot exceed the calibrated level regardless of GPS or FC state. It is not as elegant as closed-loop speed limiting, but it is fail-safe: if GPS is lost, the throttle cap remains active.

Connections¶

requires: - betaflight-setup related: - betaflight-gps-rescue - lipo-batteries - pid-proportional-term - a2-throttle-compliance leads_to: - betaflight-gps-rescue - a2-throttle-compliance