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
save
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.
Hi Oscar, one question to ask ,
If I set failsafe on my transmitter for quad to power down the motors and drop , and I was to set up gps RTH as failsafe also ,
Question, what failsafe will the quad take orders from ?
Will it drop or RTH?
Thank you Oscar I’m learning a lot for your blog
Very new to the hobby
look at these as layers… TX, RX and FC, these are all layers.
The closest layer to your motors is the FC, so the quad will react to the FC failsafe layer first.
This is assuming you are using SBUS or CRSF, where the RX will send a “Failsafe flag” to the FC.
home arrow in Betaflight OSD says wrong direction and when turn on rescue going away from me——-why
not enough satellites? Or GPS module is interfered by VTX? Try further separation.
Hello Oscar! I have a question and think may know now but want to MAKE SURE…For the first trial with the rescue mode has me puzzled but I think that may be clear now as well…. Okay first time I tried it, it seemed to start to work, it went straight up I guess the the altitude have set but then dropped from the sky?! Now I think that is prob due to I turned GPS Rescue back off then tried to turn it back on, and after reading your article that seems to make it drop??…I think? as well as I “may” have disarmed it and rearmed it to try to get the “failsafe” rescue to kick in and prob re-set the “home” location?! Alright I am about to try it again now after doing some adjusting, BUT MY BIG question is “Which way should the arrow point for home” down?? For if I remember correctly I did watch someones video on this after my failure, and I believe and PLEASE TELL ME, when arrow is pointing downward is that pointing to “home” for I just flew it and seems that was direction it was when I was some distance away, and in the video I watched I DID notice that when rescue is activated the arrow JUMPS STRAIGHT UP on it’s return, so I still am confused?!! So which way should the arrow be pointing when I have it away from me and should be pointing “home”?? PLEASE let me know for need to test it again, but I almost lost it the first time just got lucky finding it somewhat. Thanks I greatly appreciate it!
If the arrow points up in OSD, means it’s flying away from home. If it points down, it means the quad is facing home.
please could you help I have put gps on my quad tested it in my garden with props off so got 8 sats come up when I flicked the switch the motors go very fast ,my question is why should it do this when it is not 100 m away ,should it have gone into failsafe and cut the motors ,I have set all the cli commands as you have and am running 3.5.1
Hi Oscar, would you know why I can get Rescue mode to work faultlessly when I activate it with a switch but when I try to activate it with failsafe either with Failsafe set to a switch or by turning off the transmitter it just disarms.
Rescue mode only works when the quad is further than 100m away (or any distance you set), within this distance you quad will just drop/disarm.
If this is not the case then you need to play with Insanity-Check’s options.
When testing GPS Rescue, make sure you land and disarm between tests. This is because the rescue altitude is set to the highest altitude you reach during flight or the minimum setting number (whichever is greater, ie. the quad will never descend when rescue is activated, it will only ascend or maintain altitude). If you do multiple rescue tests without disarming, then the minimum altitude can stack higher and higher depending on how high you are flying and each test the quad will climb a little bit higher due to the altitude error stacking.
Thanks for explaination!
What will drone doing when he returns to home, will it land automatically and disarm? For example if i have problems with radio.
No, it will not land but drop. Make sure to regain control.
Does anyone know whether this is possible using a FRSky GPS module? I have a feeling it’s not, and that the FrSKy only connects to the FrSky receiver not directly to the flight controller.
Hello Oscar. Thank you for the wonderful post.
Hi Oscar. Thank you so so much for this information. I have a question based on the last section of your blog. If I set Gps rescue to failsafe and I experience failsafe and lose video at the same time. My quad starts heading back and it reconnects to my quad, but I am flying blind. U said set the switch to failsafe as well. How do I set both up, failsafe and switch if I can only chose one mode. Please advice. Thank you. I have learnt a lot.
Setup GPS Rescue mode on a switch, so when failsafe happens, you should also flip the GPS Rescue mode switch.
Good information Oscar. I installed mine a couple of weeks ago (mini ublox M8N) strictly for lost quad location. I went out to check it out but due to a FC malfunction my quad went wildly out of control before i had a chance to ‘test’ the install. Long story short, got my GPS coordinates from my DVR, plugged them into my smartphone and it got me within 50 feet of my quad. :) With out the GPS i probably would have been hours trying to find the quad.
that’s good to hear bro!
I have experience the “drone falling out of the sky” issue. My question is: Why would sanity check make the quad behave properly when it doesn’t do that by arming through a switch. Have you test that? I have sanity check off because of this reason as of right now.
it’s really a hit and miss issue at the moment with Sanity Check. Make sure you understand the risk of turning it off. Sometimes it’s better to lose your quad than damaging something or someone more important.
Hi Oscar ! there’s one important detail in:
set gps_rescue_initial_alt = 50
where 50 is Alt in meters. this value means Absolute alt or above takeoff ?
because in my place Absolute hight ( ground level ) is about 180 meters so if I write 50 meters my drone becomes a suicide machine )))
It’s the height from ground :) so setting that to 50 would be 230m in your cause
Hi Oscar,
non-failsafe scenario question:
is it possible to take back the control if the mode was activated previously w. a switch?
If I turn the mode off w. the switch within the minimum range (before the quad “lands”) it falls from the sky.
BF3.4
thanks,
WP
Yea if it was activated with a switch, you can put it back in acro mode anytime using that switch. What’s your Sanity setting?
Thanks for this post! My next build will probably be a 6inch for mid/long range with gps, so this tutorial it’s perfect
When I first tested this (less than descent distance) it just disarmed in flight.Does any modification beed to be made to the sanity checks tonprevent this?
You can try
set gps_rescue_sanity_checks = RESCUE_SANITY_FS_ONLY
or even OFF, but that’s not recommended according to the wiki.
You need to be beyond the minimum range of 100m, maybe its set as part of descent distance, not sure on that. The disarm I believe is a safety measure so the drone doesn’t fly autopilot straight into you being so close to its home coordinates. Personally I would like to see a safety check added that if it is activated by switch within the 100m range, it simply does nothing but beeps an alarm onscreen “proximity” or something instead of dropping out of the sky.