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Improve documentation for motor failure injection and detection (#25756)
* failure_injection: improve previously vague motor faulure Reading it again I decided adding the sentance in 4d2170c13ea4d42c5b0b464dbbcbb68fb098cbcc is not clear enough. * docs/safety: add a motor failure detection paragraph The functionality is in my eyes pretty basic but so far completely undocumented so I went through the code and added a paragraph based on questions I received. * Subedit * Apply suggestion from @hamishwillee --------- Co-authored-by: Hamish Willee <hamishwillee@gmail.com>
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Matthias Grob
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@ -207,7 +207,7 @@ The relevant parameters shown below.
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### Position Loss Failsafe Action
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Multicopters will switch to [Altitude mode](../flight_modes_mc/altitude.md) if a height estimate is available, otherwise [Stabilized mode](../flight_modes_mc/manual_stabilized.md).
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Fixed-wing planes, and VTOLs not configured to land in hover ([NAV_FORCE_VT](../advanced_config/parameter_reference.md#NAV_FORCE_VT)), have a parameter ([FW_GPSF_LT](../advanced_config/parameter_reference.md#FW_GPSF_LT)) that defines how long they will loiter (circle with a constant roll angle ([FW_GPSF_R](../advanced_config/parameter_reference.md#FW_GPSF_R)) at the current altitude) after losing position before attempting to land.
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If VTOLs have are configured to switch to hover for landing ([NAV_FORCE_VT](../advanced_config/parameter_reference.md#NAV_FORCE_VT)) then they will first transition and then descend.
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@ -276,12 +276,12 @@ The relevant parameters are listed in the table below.
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## Failure Detector
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The failure detector allows a vehicle to take protective action(s) if it unexpectedly flips, or if it is notified by an external failure detection system.
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The failure detector allows a vehicle to take protective actions if it unexpectedly flips, detects a motor failure, or if it is notified by an external failure detection system.
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During **flight**, the failure detector can be used to trigger [flight termination](../advanced_config/flight_termination.md) if failure conditions are met, which may then launch a [parachute](../peripherals/parachute.md) or perform some other action.
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::: info
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Failure detection during flight is deactivated by default (enable by setting the parameter: [CBRK_FLIGHTTERM=0](#CBRK_FLIGHTTERM)).
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Acting on a detected failure during flight is deactivated by default (enable by setting the parameter: [CBRK_FLIGHTTERM=0](#CBRK_FLIGHTTERM)).
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:::
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During **takeoff** the failure detector [attitude trigger](#attitude-trigger) invokes the [disarm action](#act_disarm) if the vehicle flips (disarm kills the motors but, unlike flight termination, will not launch a parachute or perform other failure actions).
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@ -303,6 +303,26 @@ The relevant parameters are shown below:
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| <a id="FD_FAIL_P_TTRI"></a>[FD_FAIL_P_TTRI](../advanced_config/parameter_reference.md#FD_FAIL_P_TTRI) | Time to exceed [FD_FAIL_P](#FD_FAIL_P) for failure detection (default 0.3s). |
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| <a id="FD_FAIL_R_TTRI"></a>[FD_FAIL_R_TTRI](../advanced_config/parameter_reference.md#FD_FAIL_R_TTRI) | Time to exceed [FD_FAIL_R](#FD_FAIL_R) for failure detection (default 0.3s). |
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### Motor Failure Trigger
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The failure detector can be configured to detect a motor failure while armed (and trigger an associated action) in the following conditions:
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- A 300 ms timeout occurs in telemetry from an ESC that was previously available.
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- The input current in the telemetry of an ESC which was previously positive gets too low for more than [`FD_ACT_MOT_TOUT`](FD_ACT_MOT_TOUT) ms.
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The "too low" condition is defined by:
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```text
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{esc current} < {parameter FD_ACT_MOT_C2T} * {motor command between 0 and 1}
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```
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| Parameter | Description |
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| -------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| <a id="FD_ACT_EN"></a>[FD_ACT_EN](../advanced_config/parameter_reference.md#FD_ACT_EN) | Enable/disable the motor failure trigger completely. |
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| <a id="FD_ACT_MOT_THR"></a>[FD_ACT_MOT_THR](../advanced_config/parameter_reference.md#FD_ACT_MOT_THR) | Minimum normalized [0,1] motor command below which motor under current is ignored. |
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| <a id="FD_ACT_MOT_C2T"></a>[FD_ACT_MOT_C2T](../advanced_config/parameter_reference.md#FD_ACT_MOT_C2T) | Scale between normalized [0,1] motor command and expected minimally reported currrent when the rotor is healthy. |
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| <a id="FD_ACT_MOT_TOUT"></a>[FD_ACT_MOT_TOUT](../advanced_config/parameter_reference.md#FD_ACT_MOT_TOUT) | Time in miliseconds for which the under current detection condition needs to stay true. |
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| <a id="CA_FAILURE_MODE"></a>[CA_FAILURE_MODE](../advanced_config/parameter_reference.md#CA_FAILURE_MODE) | Configure to not only warn about a motor failure but remove the first motor that detects a failure from the allocation effectiveness which turns off the motor and tries to operate the vehicle without it until disarming the next time. |
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### External Automatic Trigger System (ATS)
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The [failure detector](#failure-detector), if [enabled](#CBRK_FLIGHTTERM), can also be triggered by an external ATS system.
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@ -19,7 +19,7 @@ At time of writing (PX4 v1.14):
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## Failure System Command
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Failures can be injected using the [failure system command](../modules/modules_command.md#failure) from any PX4 console/shell, specifying both the target and type of the failure.
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Failures can be injected using the [failure system command](../modules/modules_command.md#failure) from any PX4 [console/shell](../debug/consoles.md) (such as the [QGC MAVLink Console](../debug/mavlink_shell.md#qgroundcontrol-mavlink-console) or SITL _pxh shell_), specifying both the target and type of the failure.
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### Syntax
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@ -61,12 +61,19 @@ where:
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- _instance number_ (optional): Instance number of affected sensor.
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0 (default) indicates all sensors of specified type.
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### Example
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## MAVSDK Failure Plugin
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The [MAVSDK failure plugin](https://mavsdk.mavlink.io/main/en/cpp/api_reference/classmavsdk_1_1_failure.html) can be used to programmatically inject failures.
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It is used in [PX4 Integration Testing](../test_and_ci/integration_testing_mavsdk.md) to simulate failure cases (for example, see [PX4-Autopilot/test/mavsdk_tests/autopilot_tester.cpp](https://github.com/PX4/PX4-Autopilot/blob/main/test/mavsdk_tests/autopilot_tester.cpp)).
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The plugin API is a direct mapping of the failure command shown above, with a few additional error signals related to the connection.
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## Example: RC signal
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To simulate losing RC signal without having to turn off your RC controller:
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1. Enable the parameter [SYS_FAILURE_EN](../advanced_config/parameter_reference.md#SYS_FAILURE_EN). And specifically to turn off motors also [CA_FAILURE_MODE](../advanced_config/parameter_reference.md#CA_FAILURE_MODE).
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1. Enter the following commands on the MAVLink console or SITL _pxh shell_:
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1. Enable the [SYS_FAILURE_EN](../advanced_config/parameter_reference.md#SYS_FAILURE_EN) parameter.
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2. Enter the following commands on the MAVLink console or SITL _pxh shell_:
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```sh
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# Fail RC (turn publishing off)
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@ -76,9 +83,18 @@ To simulate losing RC signal without having to turn off your RC controller:
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failure rc_signal ok
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```
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## MAVSDK Failure Plugin
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## Example: Motor
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The [MAVSDK failure plugin](https://mavsdk.mavlink.io/main/en/cpp/api_reference/classmavsdk_1_1_failure.html) can be used to programmatically inject failures.
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It is used in [PX4 Integration Testing](../test_and_ci/integration_testing_mavsdk.md) to simulate failure cases (for example, see [PX4-Autopilot/test/mavsdk_tests/autopilot_tester.cpp](https://github.com/PX4/PX4-Autopilot/blob/main/test/mavsdk_tests/autopilot_tester.cpp)).
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To stop a motor mid-flight without the system anticipating it or excluding it from allocation effectiveness:
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The plugin API is a direct mapping of the failure command shown above, with a few additional error signals related to the connection.
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1. Enable the [SYS_FAILURE_EN](../advanced_config/parameter_reference.md#SYS_FAILURE_EN) parameter.
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2. Enable [CA_FAILURE_MODE](../advanced_config/parameter_reference.md#CA_FAILURE_MODE) parameter to allow turning off motors.
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3. Enter the following commands on the MAVLink console or SITL _pxh shell_:
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```sh
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# Turn off first motor
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failure motor off -i 1
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# Turn it back on
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failure motor ok -i 1
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```
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