GPS Rescue mode in Betaflight is similar to “Return to Home”. When you lose video or radio signal, the quad is supposed to return to you using GPS.
Don’t expect it to work like your DJI drone, because it doesn’t, yet. The quad doesn’t go back to exactly where it was launched, but close enough so you can get your signals back and allot you to regain control. It’s a useful feature to have in Betaflight if you fly long range, and it might save your drone one day :)
Check out my other Betaflight Tutorials.
Requirement for GPS Rescue Mode
- Flash your FC to Betaflight 3.5 or newer
- Tutorial: Setup a GPS module on your FC
- Enable Accellerometer (so it can detect the angle of the quad)
This is the GPS module i use, product page – http://bit.ly/2KZcdR7
Barometer is not required, but recommended. It’s used to calculate the altitude of the quad. If you don’t have this, altitude can be calculated with data from the GPS module, but not as accurate as having a barometer. The Kakute F7 FC has barometer built-in.
Compass is not required and not used in Rescue Mode.
GPS Rescue Mode Configuration
Once you have setup GPS module, all that left is just software configuration.
You have to tweak the settings to make it work for your particular setup and environment. Make sure to check out the Betaflight wiki to fully understand what the parameters do: https://github.com/betaflight/betaflight/wiki/GPS-rescue-mode
In CLI, type in “get gps”, and you will get the list of GPS related parameters. Here I will show you the settings I changed in my quad.
set gps_rescue_min_dth = 100
Minimum distance to home – How far the quad has to be from home before it will activate Rescue mode. Default is 100 meters, but you can reduce it as little as 50 meters. This is to prevent activating Rescue mode when the quad is too close and endangering yourself by flying your quad accidentally to your face :)
set gps_rescue_min_sats = 6
Your quad won’t arm if the GPS has fewer locked on satellites than this parameter, so you might want to set it lower or even zero if you don’t want to wait before every flight. When you want to use GPS, then you just need to wait until it sees enough GPS before taking off :) (you can put that in OSD)
Note that if you take off before the GPS sees enough satellites, it won’t know where home is. Recommended number of Sats: 6 to 8.
set gps_rescue_angle = 45
It’s in degree. You might want to use a higher angle than the default 30, in case the quad isn’t strong enough to fight head wind. However if the angle is too steep it might struggle to stay in the air so it really depends on the power of your quad. You need to enable Accellerometer and need to be calibrated/trimmed properly for this to work accurately. If your ACC is faulty, rescue mode might not work correctly for you. Verify by flying in Angle mode. If so replace FC.
set gps_rescue_descent_distance = 200
It’s in meters, at what distance from home our drone starts to descent. Enter a distance which you think you should get your signals back reliably.
set gps_rescue_initial_alt = 50
It’s in meters, at what height the drone returns home. It should be high enough to avoid trees, buildings and power lines. But not too high so you can still see and hear it line of sight, and not wasting too much battery just climbing.
set gps_rescue_ground_speed = 1000
It’s in cm/s, at what speed the quad travels back. I find the default 2000cm/s a bit too fast so I set it to half that speed, 1000cm/s is about 36Km/hr.
set gps_rescue_sanity_checks = RESCUE_SANITY_FS_ONLY
Some people have unexplained disarm during rescue mode. This might be caused by this sanity check when it’s turned on. According to the wiki it’s not recommended to be turned off, otherwise if the quad hits something it won’t disarm and just keep spinning the motors.
The wiki also recommends setting it to “FS_Only” (Failsafe Only) if you are having trouble with the option “On”, which turns it off when it’s activated by a switch but only turns on when it’s in failsafe.
It’s really a hit and miss issue at the moment, and some people decided to just turn it off completely. But beware of the risk by doing so.
Activating GPS Rescue Feature
There are two ways to activate GPS Rescue mode, either by Failsafe, or a switch on your transmitter. I recommend setting it up on a switch first for testing before using it for failsafe.
Go to the Betaflight Modes tab and add a switch/AUX channel for GPS Rescue Mode.
Testing GPS Rescue Mode
Remove all props, verify that the GPS Rescue mode can actually get activated by the switch, and you can switch back to acro mode.
Keep in mind that the settings depend on your model and the environment so make sure to test it fully. Do this in an open field without any obstacles and people.
These GPS related elements in your OSD will help you understand what your quad is doing.
Make sure you have enough locked satellites in the OSD before testing.
Remember don’t disarm and re-arm your quad during flight, before arming resets the home location.
Fly in a straight line, past your descent distance and a bit more. For example, if your descent distance setting is 200 meters, fly 300-400 meters away.
Pay attention to the home arrow in Betaflight OSD, make sure it’s pointing towards home. If it’s pointing other direction then there is probably something wrong, and do not activate GPS Rescue mode. Otherwise your quad would return someone else’s home!
Using GPS_Rescue for Failsafe
Once you know it’s working reliably, you can set it up for failsafe. In CLI type
set failsafe_procedure = GPS-RESCUE
Note that your quad will enter rescue mode if RC signal is lost, and it will go back to acro mode when RC signal is restored. At this point it’s possible that your video signal is still lost and you are flying blind!
So it’s important to assign rescue mode to a switch. When failsafe happens, put your switch to rescue mode as well. Only put your switch back to acro mode when you are ready to take over control.
What Happens when Rescue Mode is Activated?
The quad climbs or drops to a certain altitude, then it yaws around and starts going toward the direction of launch point. When it reaches the “descent distance” from home, it will start to descent. It’s not as advanced as DJI drones, it will just descent and crash unless you take control.