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71 lines
3.3 KiB
Markdown
71 lines
3.3 KiB
Markdown
# Simulate Failsafes
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[Failsafes](../config/safety.md) define the safe limits/conditions under which you can safely use PX4, and the action that will be performed if a failsafe is triggered (for example, landing, holding position, or returning to a specified point).
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In SITL some failsafes are disabled by default to enable easier simulation usage.
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This topic explains how you can test safety-critical behavior in SITL simulation before attempting it in the real world.
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::: info
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You can also test failsafes using [HITL simulation](../simulation/hitl.md).
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HITL uses the normal configuration parameters of your flight controller.
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:::
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## Data Link Loss
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The _Data Link Loss_ failsafe (unavailability of external data via MAVLink) is enabled by default.
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This makes the simulation only usable with a connected GCS, SDK, or other MAVLink application.
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Set the parameter [NAV_DLL_ACT](../advanced_config/parameter_reference.md#NAV_DLL_ACT) to the desired failsafe action to change the behavior.
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For example, set to `0` to disable it.
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::: info
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All parameters in SITL including this one get reset when you do `make clean`.
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:::
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## RC Link Loss
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The _RC Link Loss_ failsafe (unavailability of data from a remote control) is enabled by default.
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This makes the simulation only usable with either an active MAVLink or remote control connection.
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Set the parameter [NAV_RCL_ACT](../advanced_config/parameter_reference.md#NAV_RCL_ACT) to the desired failsafe action to change the behavior.
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For example, set to `0` to disable it.
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::: info
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All parameters in SITL including this one get reset when you do `make clean`.
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:::
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## Low Battery
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The simulated battery is implemented to never run out of energy, and by default only depletes to 50% of its capacity and hence reported voltage.
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This enables testing of battery indication in GCS UIs without triggering low battery reactions that might interrupt other testing.
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To change this minimal battery percentage value use the parameter [SIM_BAT_MIN_PCT](../advanced_config/parameter_reference.md#SIM_BAT_MIN_PCT).
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To control how fast the battery depletes to the minimal value use the parameter [SIM_BAT_DRAIN](../advanced_config/parameter_reference.md#SIM_BAT_DRAIN).
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:::tip
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By changing [SIM_BAT_MIN_PCT](../advanced_config/parameter_reference.md#SIM_BAT_MIN_PCT) in flight, you can also test regaining capacity to simulate inaccurate battery state estimation or in-air charging technology.
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:::
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It is also possible to disable the simulated battery using [SIM_BAT_ENABLE](../advanced_config/parameter_reference.md#SIM_BAT_ENABLE) in order to, for example, provide an external battery simulation via MAVLink.
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## Sensor/System Failure
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[Failure injection](../debug/failure_injection.md) can be used to simulate different types of failures in many sensors and systems.
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For example, this can be used to simulate absent or intermittent GPS, RC signal that has stopped or got stuck on a particular value, failure of the avoidance system, and much more.
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For example, to simulate GPS failure:
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1. Enable the parameter [SYS_FAILURE_EN](../advanced_config/parameter_reference.md#SYS_FAILURE_EN).
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1. Enter the following commands on the SITL instance _pxh shell_:
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```sh
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# Turn (all) GPS off
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failure gps off
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# Turn (all) GPS on
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failure gps ok
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```
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See [System Failure Injection](../debug/failure_injection.md) for a list of supported target sensors and failure modes.
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