2.7 KiB
Copter Loiter Brake
This script implements an emergency change to BRAKE mode in copter if you are in LOITER mode and break a terrain altitude limit. The script is useful when flying in LOITER mode in steep terrain.
Parameters
The script adds the following parameters to control it's behaviour.
TERR_BRK_ENABLE
This must be set to 1 to enable the script.
TERR_BRK_ALT
This is the terrain altitude threshold for engaging BRAKE mode. The onboard terrain system must be enabled with TERRAIN_ENABLE=1 and terrain must have either been preloaded to the vehicle (see https://terrain.ardupilot.org ) or be available from the ground station over MAVLink.
Make sure you set sufficient margin to cope with obstacles such as trees or any local towers or other obstacles.
TERR_BRK_HDIST
This is the distance from home for the BRAKE checking to be enabled. The default of 100 meters is good for most operations. This threshold allows you to take over in LOITER mode for low altitude operations and takeoff/landing when close to home.
TERR_BRK_SPD
This is a speed threshold BRAKE checking to be enabled. If both the horizontal speed and the descent rate are below this threshold then BRAKE will not be engaged. This defaults to zero which means no speed checking is performed.
You should set this to a small value if you want to be able to recover from BRAKE mode by climbing straight up in LOITER mode. A value of 0.5 m/s is recommended. The value needed will be dependent on the amount of noise there is in your velocity measurement and how gusty the wind is, but 0.5 should work in most applications.
If you set this value then to recover in LOITER mode you should raise the throttle stick to demand climb before you switch back to LOITER mode. The positive climb rate means BRAKE will not re-engage.
Operation
Install the lua script in the APM/SCRIPTS directory on the flight controllers microSD card. Review the above parameter descriptions and decide on the right parameter values for your vehicle and operations.
Make sure TERRAIN_ENABLE is 1 and you should preload terrain data for the flight area from https://terrain.ardupilot.org
It is strongly recommended that you set TERRAIN_SPACING=30 and preload the SRTM1 terrain data for 30m horizontal resolution of terrain data.
When the system engages you will see a message like this "Terrain 29.2m - BRAKE" where in this example you are 29.2m above the terrain.
To recover you could use GUIDED mode, or RTL (make sure you have set RTL_ALT_TYPE to terrain) or if you have set TERR_BRK_SPD to a positive value then you could raise the throttle stick and switch back to LOITER mode.
If the system is continually giving false positives then set TERR_BRK_ENABLE to zero to disable.