PX4 parameters Foxborne reads
Check how a vehicle was set to react to a lost link, a lost offboard stream or lost GNSS. These are the eight PX4 parameters Foxborne reads from every flight log, with PX4 v1.16 defaults and ranges.
On this page15
Foxborne reads eight failsafe parameters from each flight log it imports and compares them run to run. They set how long PX4 waits after losing the ground link, the offboard stream or GNSS, and what it does next. The vehicle's page shows the latest values and the changes between runs.
The PX4 facts on this page come from the PX4 v1.16.0 parameter definitions. The descriptions and value labels in the second column are the console's own.
At a glance#
| Parameter | Console description | PX4 type | PX4 default | PX4 range |
|---|---|---|---|---|
COM_DL_LOSS_T | Seconds without a ground heartbeat before the data link failsafe | int32 | 10 s | 5 to 300 s |
NAV_DLL_ACT | Data link loss action | enum | 0, Disabled | 0, 1, 2, 3, 5, 6 |
COM_FAIL_ACT_T | No description shown | float | 5.0 s | 0.0 to 25.0 s |
COM_OF_LOSS_T | Seconds without offboard setpoints before the offboard failsafe | float | 1.0 s | 0 to 60 s |
COM_OBL_RC_ACT | Offboard loss action | enum | 0, Position mode | 0 to 7 |
COM_POS_FS_EPH | Horizontal accuracy that invalidates position, metres | float | 5.0 m | -1 to 400 m |
SYS_HAS_NUM_GNSS | GNSS receivers expected | See below | See below | See below |
COM_GNSSLOSS_ACT | GNSS loss action | enum | 0, Warning | 0 to 3 |
Value labels#
The console shows an action parameter as its number and label, such as 1 (Hold). PX4 names three of these values Hold mode, Return mode and Land mode; the console drops the word "mode" from them.
| Value | NAV_DLL_ACT | COM_OBL_RC_ACT | COM_GNSSLOSS_ACT |
|---|---|---|---|
| 0 | Disabled | Position mode | Warning |
| 1 | Hold | Altitude mode | Return |
| 2 | Return | Stabilized | Land |
| 3 | Land | Return | Terminate |
| 4 | Not defined | Land | Not defined |
| 5 | Terminate | Hold | Not defined |
| 6 | Disarm | Terminate | Not defined |
| 7 | Not defined | Disarm | Not defined |
Parameter details#
COM_DL_LOSS_T#
- PX4 description
- GCS connection loss time threshold
- Default and range
- 10 s, from 5 to 300 s in steps of 1 s
PX4 starts this timer from the last telemetry_status report that still carried a ground station heartbeat, not from the heartbeat itself (Commander.cpp, dataLinkCheck()). In INC-0143, UGV-02 held 11.88 s after the last ground heartbeat reached it, and 10.007 s after that last report.
NAV_DLL_ACT#
- PX4 description
- Set GCS connection loss failsafe mode
- Default and values
- 0 (Disabled). Also 1 Hold, 2 Return, 3 Land, 5 Terminate, 6 Disarm.
PX4 enters the ground connection loss failsafe only after the COM_DL_LOSS_T timeout, then runs the action this parameter selects. In INC-0143, NAV_DLL_ACT 1 selected Hold.
COM_FAIL_ACT_T#
- PX4 description
- Delay between failsafe condition triggered and failsafe reaction
- Console description
- None shown
- Default and range
- 5.0 s, from 0.0 to 25.0 s. A value of 0 disables the delay.
Before a delayed failsafe action, PX4 waits this long in Hold mode, and the pilot can switch modes meanwhile. PX4 applies no delay when the action is Warn, Hold, Disarm or Terminate (framework.cpp). That is why the INC-0143 event page lists it as 5 s (not applied to Hold).
COM_OF_LOSS_T#
- PX4 description
- Offboard connection loss timeout
- Default and range
- 1.0 s, from 0 to 60 s in steps of 0.01 s
After this timeout, PX4 runs the offboard loss action set by COM_OBL_RC_ACT.
COM_OBL_RC_ACT#
- PX4 description
- Set offboard loss failsafe mode
- Default and values
- 0 (Position mode). Also 1 Altitude mode, 2 Stabilized, 3 Return, 4 Land, 5 Hold, 6 Terminate, 7 Disarm.
PX4 enters the offboard loss failsafe only after the COM_OF_LOSS_T timeout.
COM_POS_FS_EPH#
- PX4 description
- Horizontal position error threshold for hovering systems
- Default and range
- 5.0 m, from -1 to 400 m. A value of -1 disables it.
PX4 uses it only for multicopters and VTOLs in hover mode. Once a position is valid, PX4 invalidates it only when the horizontal error exceeds 2.5 times this value: 12.5 m at the default. It validates the position again once the error drops below the value itself.
The example dataset lists it for the Q4 quadcopters only.
SYS_HAS_NUM_GNSS#
The console describes it as GNSS receivers expected, and every run in the example dataset logged 1. This page states no PX4 default or range for it. COM_GNSSLOSS_ACT depends on it, as the next section shows.
COM_GNSSLOSS_ACT#
- PX4 description
- GNSS loss failsafe mode
- Default and values
- 0 (Warning). Also 1 Return, 2 Land, 3 Terminate.
PX4 triggers it when the active GNSS count drops below SYS_HAS_NUM_GNSS, and never when SYS_HAS_NUM_GNSS is 0. With SYS_HAS_NUM_GNSS at 2, two receivers that report positions inconsistent with their reported accuracy also trigger it; with any other value, that case only warns. Any value above Warning also blocks arming.
Values in the example dataset#
| Parameter | Q4 recon quads | T4 tracked UGVs | Runs that differ |
|---|---|---|---|
COM_DL_LOSS_T | 10 | 10 | R-0921 on UGV-06: 5 |
NAV_DLL_ACT | 2 (Return) | 1 (Hold) | R-0917 on UGV-05: 0 (Disabled) |
COM_FAIL_ACT_T | 5 | 5 | None |
COM_OF_LOSS_T | 1 | 1 | None |
COM_OBL_RC_ACT | 5 (Hold) | 5 (Hold) | None |
COM_POS_FS_EPH | 5 | Not listed | None |
SYS_HAS_NUM_GNSS | 1 | 1 | None |
COM_GNSSLOSS_ACT | 0 (Warning) | 0 (Warning) | None |
Where the console shows them#
| Where | What it shows |
|---|---|
| Vehicle page, Failsafe parameters | The values from the latest run with a flight log, such as From R-0924, 22 Sep: name, console description and value. With no flight log it reads No flight log yet and Import a flight log to read its parameters. |
| Vehicle page, Changes between runs | A drawer opened by the change count in the Failsafe parameters header, such as 1 change between runs. Each run compared with the next older one, leaving out rejected and quarantined runs. Every change, newest first, 10 to a page, each linked to its run. |
| Event page, Context, Flight controller | One chip per parameter, such as COM_DL_LOSS_T 10. |
| Event page, Failsafe decision, Parameters in effect | The parameters behind a failsafe. INC-0143 lists COM_DL_LOSS_T 10 s, NAV_DLL_ACT 1 (Hold) and COM_FAIL_ACT_T 5 s (not applied to Hold). |
Reports quote them where they explain a finding. The INC-0142 report states that the 6.96 s receive gap was shorter than COM_DL_LOSS_T (10 s), so no failsafe was expected or recorded.
Example drift#
UGV-05 logged NAV_DLL_ACT 1 (Hold) in R-0900 on 11 Sep, 0 (Disabled) in R-0917 on 19 Sep, then 1 (Hold) again in R-0924 on 22 Sep. Its vehicle page shows 2 changes between runs, and the drawer lists them:
NAV_DLL_ACT 0 (Disabled) to 1 (Hold) in R-0924, 22 Sep
NAV_DLL_ACT 1 (Hold) to 0 (Disabled) in R-0917, 19 SepR-0917 is the berm line link test behind INC-0137. Each drift entry links to the run that logged the new value.
Related#
- Vehicles and parameter drift walks through the vehicle page.
- failsafe_entered reports each failsafe PX4 entered, with its cause.
- telemetry_gap explains why a receive gap on the ground can pass with no failsafe.
- PX4 ULog describes the flight log these values come from.