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99 lines
6.2 KiB
Markdown
99 lines
6.2 KiB
Markdown
# Land Detector Configuration
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The land detector is a dynamic vehicle model representing key vehicle states from ground contact through to landed.
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This topic explains the main parameters you may wish to tune in order to improve landing behaviour.
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## Auto-Disarming
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The land-detector automatically disarms the vehicle on landing.
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You can set [COM_DISARM_LAND](../advanced_config/parameter_reference.md#COM_DISARM_LAND) to specify the number of seconds after landing that the system should disarm (or turn off auto-disarming by setting the parameter to -1).
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## Multicopter Configuration
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The complete set of relevant landing detector parameters are listed in the parameter reference with the prefix [LNDMC](../advanced_config/parameter_reference.md#land-detector) (these can be edited in QGroundControl via the [parameter editor](../advanced_config/parameters.md)).
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:::tip
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Information about how the parameters affect landing can be found below in [Land Detector States](#mc-land-detector-states).
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:::
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Other key parameters that you may need to tune in order to improve landing behaviour on particular airframes are:
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- [MPC_THR_HOVER](../advanced_config/parameter_reference.md#MPC_THR_HOVER) - the hover throttle of the system (default is 50%).
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It is important to set this correctly as it makes altitude control more accurate and ensures correct land detection.
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A racer or a big camera drone without payload mounted might need a much lower setting (e.g. 35%).
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::: info
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Incorrectly setting `MPC_THR_HOVER` may result in ground-contact or maybe-landed detection while still in air (in particular, while descending in [Position mode](../flight_modes_mc/position.md) or [Altitude mode](../flight_modes_mc/altitude.md)).
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This causes the vehicle to "twitch" (turn down the motors, and then immediately turn them back up).
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:::
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- [MPC_THR_MIN](../advanced_config/parameter_reference.md#MPC_THR_MIN) - the overall minimum throttle of the system.
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This should be set to enable a controlled descent.
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- [MPC_LAND_CRWL](../advanced_config/parameter_reference.md#MPC_LAND_CRWL) - the vertical speed applied in the last stage of autonomous landing if the system has a distance sensor and it is present and working. Has to be set larger than LNDMC_Z_VEL_MAX.
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### MC Land Detector States
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In order to detect landing, the multicopter first has to go through three different states, where each state contains the conditions from the previous states plus tighter constraints.
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If a condition cannot be reached because of missing sensors, then the condition is true by default.
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For instance, in [Acro mode](../flight_modes_mc/acro.md) and no sensor is active except for the gyro sensor, then the detection solely relies on thrust output and time.
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In order to proceed to the next state, each condition has to be true for a third of the configured total land detector trigger time [LNDMC_TRIG_TIME](../advanced_config/parameter_reference.md#LNDMC_TRIG_TIME).
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If the vehicle is equipped with a distance sensor, but the distance to ground is currently not measurable (usually because it is too large), the trigger time is increased by a factor of 3.
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If one condition fails, the land detector drops out of the current state immediately.
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#### Ground Contact
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Conditions for this state:
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- no vertical movement ([LNDMC_Z_VEL_MAX](../advanced_config/parameter_reference.md#LNDMC_Z_VEL_MAX))
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- no horizontal movement ([LNDMC_XY_VEL_MAX](../advanced_config/parameter_reference.md#LNDMC_XY_VEL_MAX))
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- lower thrust than [MPC_THR_MIN](../advanced_config/parameter_reference.md#MPC_THR_MIN) + (hover throttle - [MPC_THR_MIN](../advanced_config/parameter_reference.md#MPC_THR_MIN)) \* (0.3, unless a hover thrust estimate is available, then 0.6),
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- additional check if vehicle is currently in a height-rate controlled flight mode: the vehicle has to have the intent to descend (vertical velocity setpoint above LNDMC_Z_VEL_MAX).
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- additional check for vehicles with a distance sensor: current distance to ground is below 1m.
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If the vehicle is in position- or velocity-control and ground contact was detected,
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the position controller will set the thrust vector along the body x-y-axis to zero.
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#### Maybe Landed
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Conditions for this state:
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- all conditions of the [ground contact](#ground-contact) state are true
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- is not rotating ([LNDMC_ROT_MAX](../advanced_config/parameter_reference.md#LNDMC_ROT_MAX))
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- has low thrust `MPC_THR_MIN + (MPC_THR_HOVER - MPC_THR_MIN) * 0.1`
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- no freefall detected
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If the vehicle only has knowledge of thrust and angular rate,
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in order to proceed to the next state the vehicle has to have low thrust and no rotation for 8.0 seconds.
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If the vehicle is in position or velocity control and maybe landed was detected,
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the position controller will set the thrust vector to zero.
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#### Landed
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Conditions for this state:
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- all conditions of the [maybe landed](#maybe-landed) state are true
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## Fixed-wing Configuration
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Tuning parameters for fixed-wing land detection:
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- [LNDFW_AIRSPD_MAX](../advanced_config/parameter_reference.md#LNDFW_AIRSPD_MAX) - the maximum airspeed allowed for the system still to be considered landed.
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Has to be a tradeoff between airspeed sensing accuracy and triggering fast enough.
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Better airspeed sensors should allow lower values of this parameter.
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- [LNDFW_VEL_XY_MAX ](../advanced_config/parameter_reference.md#LNDFW_VEL_XY_MAX) - the maximum horizontal velocity for the system to be still be considered landed.
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- [LNDFW_VEL_Z_MAX](../advanced_config/parameter_reference.md#LNDFW_VEL_XY_MAX) - the maximum vertical velocity for the system to be still be considered landed.
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- [LNDFW_XYACC_MAX](../advanced_config/parameter_reference.md#LNDFW_XYACC_MAX) - the maximal horizontal acceleration for the system to still be considered landed.
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- [LNDFW_TRIG_TIME](../advanced_config/parameter_reference.md#LNDFW_TRIG_TIME) - Trigger time during which the conditions above have to be fulfilled to declare a landing.
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::: info
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When FW launch detection is enabled ([FW_LAUN_DETCN_ON](../advanced_config/parameter_reference.md#FW_LAUN_DETCN_ON)), the vehicle will stay in "landed" state until takeoff is detected (which is purely based on acceleration and not velocity).
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:::
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## VTOL Land Detector
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The VTOL land detector is 1:1 the same as the MC land detector if the system is in hover mode. In FW mode, land detection is disabled.
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