Wednesday, July 30, 2014

FailSafe Setup

I used this document and this video for my FrSky X8R RX radio.

We want no RX pulses to be sent to the FlightController (FC) when the radio signal from the Taranis TX is lost. It's Option #2 in X8R manual-sheet. This way there is no confusion between RX and FC, and FC takes-over (as it should).

MissionPlanner / Initial Setup / Mandatory Hardware / FailSafe

Fail-Safe Options:
  • Battery
    • LowBattery: 0.0v (changes to 6.0v)
    • ReservedMah: 0.0
    • Disabled (Battery Monitoring)
  • Radio
    • Enabled always RTL
    • FS Pwm: 975
  • CGS
    • Disabled (unchecked)

Since my Nova quad has no Power Module, it's my understanding that Low_Battery and Reserved_Mah options are not really being used. Better to disable so that random/floating values don't cause a problem. The Nova's Low-Battery-Alarm (tone and flashing lights) appears to be hardware-based on PowerBoard and permanently fixed around 10.6 volts.

APM2 uses CH-3 to trigger FailSafe. Notice that when radio gets turned off, CH-3 Throttle goes to 900 pwm. Otherwise (when radio is on) it reads like all the others (990-2015). 975 is a good value because it is 15 lower than 990 and 75 higher than 900 (it's recommended that the separation ranges be 10 or more).

Do the test like in the video, and verify that it completes the test and "lands". My FC is inside quad so PROPS MUST BE REMOVED. This also appears to be a good place to test radio operation and stick throws to previously calibrated limits, Also, be sure stick movement is proportional (or linear) through entire range. You should also be able to see if something needs to be reversed (although "Holding by Landing Gear" test below is even better to test for need of channel reversals).

I can't really think of any reason to get back inside at this point. I removed rubber-bands and installed top cover screws and the propellers. Applied a little strip of clear packing-tape to prevent the puck cover from popping-off during flight or hard landing.

With props installed, I did a little "Holding by Landing Gear" test. It was just me carefully holding it by landing gear (use a helper if available). Make sure it pitches, rolls, and yaws in proper directions. Pulsing the throttle a little ... make sure all controls work and tugs Nova in proper directions. I found that Elevator was backwards. Reversed it in Taranis (the Mixer programming). I have updated my older post below about radio setup.

Current Fail-Safe (FS) Parameters:

My current ones running ArduCopter v3.1.2 with no PowerModule but I am using real-time DroidPlanner GCS, and FrSky Taranis/X8R.



  1. Excellent blog thanks mate. I have just received my CX-20 (bought it for my Father as I own a Walkera !R X350 Pro). I was checking the failsafe and noticed that if I was in 'loiter' then the failsafe would enter into RTL mode, however if I was in 'stabilse' it would not go into RTL but land. I can't see any settings on how to change this, any chance you can help please?

    1. That might be normal when testing on bench (like in video linked above).

  2. Ok great, I won't panic then. Sounds like it's time to be brave and go for a test flight. Cheers :)

  3. Areo scout, let us know how the test flight went. Thanks.


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