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Hamish Willee
2026-04-02 16:44:52 +11:00
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docs/en/advanced_config/barometer_thrust_compensation.md
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@@ -6,7 +6,7 @@ The direction and magnitude depend on sensor placement relative to the propeller
PX4 can compensate for this error by applying a correction proportional to the vertical thrust setpoint:
```
```txt
corrected_baro_alt = raw_baro_alt + SENS_BARO_PCOEF * |thrust_z|
```
@@ -39,19 +39,19 @@ The estimator refines the parameter over subsequent flights — each flight corr
2. Fly normally for at least 60 seconds with some altitude variation.
3. On disarm, the estimated `SENS_BARO_PCOEF` is saved automatically if the estimator converged.
4. Check convergence after flight:
- In the console: `baro_thrust_estimator status`
- In the console: `baro_thrust_estimator status`.
- In a log: look at the `baro_thrust_estimate` topic — `converged` should be true.
The estimator uses several convergence gates before saving:
| Gate | Threshold | Purpose |
|------|-----------|---------|
| Minimum flight time | 30 s | Allow RLS to settle |
| K variance (P[0][0]) | < 3.0 | Parameter estimate is precise |
| Prediction error | Low absolute or relative | Model fits the data |
| Thrust excitation | std > 0.05 | Enough signal to identify K |
| K stability | Stable for 10 s | Estimate is not drifting |
| Hold time | 10 s | Convergence is sustained |
| Gate | Threshold | Purpose |
| -------------------- | ------------------------ | ----------------------------- |
| Minimum flight time | 30 s | Allow RLS to settle |
| K variance (P[0][0]) | < 3.0 | Parameter estimate is precise |
| Prediction error | Low absolute or relative | Model fits the data |
| Thrust excitation | std > 0.05 | Enough signal to identify K |
| K stability | Stable for 10 s | Estimate is not drifting |
| Hold time | 10 s | Convergence is sustained |
::: tip
Altitude changes during hover provide the thrust excitation the estimator needs.
@@ -60,11 +60,11 @@ Constant-thrust hover with no altitude variation will not converge.
### Parameters
| Parameter | Default | Description |
|-----------|---------|-------------|
| [SENS_BARO_PCOEF](../advanced_config/parameter_reference.md#SENS_BARO_PCOEF) | 0.0 | Baro altitude correction per unit vertical thrust \[m\]. Identified by the estimator or set manually. |
| [SENS_BAR_AUTOCAL](../advanced_config/parameter_reference.md#SENS_BAR_AUTOCAL) | 1 | Bitmask: bit 0 = GNSS altitude offset, bit 1 = online thrust compensation. Set to 3 for both. |
| [SENS_BAR_CF_BW](../advanced_config/parameter_reference.md#SENS_BAR_CF_BW) | 0.1 | CF crossover frequency \[Hz\]. Lower = more conservative, higher = faster identification but noisier. |
| Parameter | Default | Description |
| ------------------------------------------------------------------------------ | ------- | ----------------------------------------------------------------------------------------------------- |
| [SENS_BARO_PCOEF](../advanced_config/parameter_reference.md#SENS_BARO_PCOEF) | 0.0 | Baro altitude correction per unit vertical thrust \[m\]. Identified by the estimator or set manually. |
| [SENS_BAR_AUTOCAL](../advanced_config/parameter_reference.md#SENS_BAR_AUTOCAL) | 1 | Bitmask: bit 0 = GNSS altitude offset, bit 1 = online thrust compensation. Set to 3 for both. |
| [SENS_BAR_CF_BW](../advanced_config/parameter_reference.md#SENS_BAR_CF_BW) | 0.1 | CF crossover frequency \[Hz\]. Lower = more conservative, higher = faster identification but noisier. |
### Soft Guards
@@ -91,19 +91,19 @@ If you prefer not to use the online estimator, you can identify `SENS_BARO_PCOEF
The script automatically selects an analysis mode based on available data:
| Mode | Data Required | Output |
|------|--------------|--------|
| Estimator review | Online estimator logged | K convergence, residual analysis |
| Full validation | Estimator + range sensor | Cross-validation of online vs offline K |
| Standalone calibration | Range sensor only | Recommended PCOEF from least-squares fit |
| Mode | Data Required | Output |
| ---------------------- | ------------------------ | ---------------------------------------- |
| Estimator review | Online estimator logged | K convergence, residual analysis |
| Full validation | Estimator + range sensor | Cross-validation of online vs offline K |
| Standalone calibration | Range sensor only | Recommended PCOEF from least-squares fit |
## Interpreting Results
| Metric | Good | Marginal | Poor |
|--------|------|----------|------|
| Metric | Good | Marginal | Poor |
| ------------------------ | ----- | --------- | ----- |
| Thrust correlation \|r\| | > 0.6 | 0.3 - 0.6 | < 0.3 |
| Model R^2 | > 0.3 | 0.1 - 0.3 | < 0.1 |
| Compensated \|r\| | < 0.2 | 0.2 - 0.4 | > 0.4 |
| Model R^2 | > 0.3 | 0.1 - 0.3 | < 0.1 |
| Compensated \|r\| | < 0.2 | 0.2 - 0.4 | > 0.4 |
- **Low R^2**: Thrust is not the dominant baro error source. Check for thermal drift, ground effect, or sensor placement issues.
- **Online/offline K disagreement > 2 m**: The estimator may need more excitation. Fly longer or with more altitude variation.
docs/en/sensor/barometer.md
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@@ -76,5 +76,6 @@ Notes:
## See Also
- [Barometer Thrust Compensation](../advanced_config/barometer_thrust_compensation.md) — compensating for propwash-induced barometer error
- [Baro driver source code](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers/barometer)
- [Modules Reference: Baro (Driver)](../modules/modules_driver_baro.md) documentation.