Strange behaviour for failsafe short.- dropping back to manual.


I am setting up a new instillation of the Arduplane and trying to configure failsafe short.

I have set up and observed the channel 3 behaviour in the failsafe screen.

I have ‘taught’ the RX that the throttle can go to about 980ms and when I turn the TX off the channel 3 display confirms this, however it goes into ‘circle’ for about 1 sec and then back to manual until the long failsafe kicks in then RTL.


The thing that seems really odd, if I use the trim to get the throttle below the trigger (I have set 1000) then all works OK but if the same throttle setting is achieved by switching off the above occurs.

I am using an Aurora9 and have tried the RX in both its available modes.


Just to confirm. The channel 3 output IS going below the trigger but Short failsafe only activates if I test this with throttle trim.


It is not just a incorrect report as there is no corrective servo action from the plane if moved.


Please help. I dont want to fly until its sorted.

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Just configured a ‘work around’ and set a RX failsafe on channel 8 in the RTL PWM range. It works but I thought the condition of all other channels would be ignored if channel 3 dropped below the trigger (with throttle failsafe active)?


Worryingly, I got to the edge of the TX range today in auto (much less than I expected at 600mts). Telemetry showed the throttle channel dropping to 900 and the mode channel going to FBW-B even though I had set a RX failsafe of RTL on the channel. It should not have mattered as 900 on the throttle channel should have forced a failsafe circ>RTL but it did not.

Fortunately it was only in FBW-B for a few seconds before TX reception was regained.

This is not good at all. Throttle failsafe is not behaving as advertised and I was lucky to get away with it.


Would be good to get a developer comment please.


Further update on failsafe issues.


The graph below was taken from yesterdays flight when there was poor 2.4GHZ reception.

Ch3 clearly drops below 1000ms, my set point. If I understand this correctly TFS should be triggered, however the APM went into FBW-B, presumably because Ch8 defaulted to 1498, which I had set as FBW-B.





So whats going on?

I have been simulating long range this morning be putting the TX (aurora 9) into low power mode and shutting it in a cupboard. I have seen numerous occurrences of the above.

If I just turn off the TX all behaves as it should, Circ then RTL. As a side issue, I had set Ch8 RX failsafe to 1300 (RTL)which is does if I turn off the TX but it seems my RX likes to put out 1498 on Ch8 when its trying to decide if the signal is lost, so I have swapped around the flight modes to make this RTL. BUT, unless I’ve misunderstood all this, all other channels are irrelevant if Ch3 is below the trigger and has been set up correctly?


In the mean time, further long range simulations have now ended up in ‘safe’ modes.


Apologies if Im doing something wrong but I have now spent a long time studying this.



What are the short and long failsafe actions configured to in the parameters page of mp?

There was another post on someone having a similar issue only reverting to manual but they didnt have the intermittant 1500 while thinking.

Short – Circle.


The other 3DR one – not configured.


Its not dropping into manual anymore because I have set a RX failsafe on CH8, now RTL. But am I right in thinking that it SHOULD be irrelevant if CH3 has dropped below preset trigger?

Will look for the other post


Of course I could disable the APM failsafe and just have the RX failsafe set the required mode but that would not allow long/short options.

What are most people doing?


Not sure. I had a little failsafe issue myself. Trying to understand the most foolproof method and use it. I have reconfigured my modes also. I am thinking that tx/rx should be set to failsafe throttle pulse at its lowest point. Useable throttle range well above that with mp failsafe active and threshold well below min useable throttle just like it says in Wiki. My question is when setting up mp flight modes, should your manual mode be set to high pulse and flight mode 6? Or, should that be left unused for something the apm uses like auto switch to manual for internal apm failure? If you can config your transmitter to failsafe to a mode, which should it be?
Scott, I have all 6 modes set up on the TX so all modes are assigned. I dont think you can change the manual one from 1750+ (but you may be able to have another mode manual). Im not sure what you mean about the APM failing and switching to manual. Does it do that?

I have just been trying to get the TX/RX on the limit of reception (on the ground) and then replaying the tlog to see what PWM the channels (particularly Ch8) go to. Of course they SHOULD go to the set failsafe but there seems to be a grey area.
Suggest you try the same. It seems switching off the TX is not quite the same as being on the range limit.

I am still pretty new to all this so please bear with me.  The Wiki says:

"Note that Flight Mode 6 cannot be changed from Manual. It's "hardware manual", which means that it's controlled by the failsafe circuit on the APM board to always be able to return you to RC control as a safety measure." 

I may have read too much into that.  Lots of failsafes here.  Tx, throttle activated and gcs.  It also says the failsafe only:

  • Detect complete loss of RC signal (if the RC receiver is able to generate a predictable signal-loss behavior) and initiate a defined auto-mode response, such as returning to home. Some RC equipment can do this, and some can't (see below for details on how to use it if yours supports this function). 
  • Detect loss of telemetry for more than 20 sec and switch to return to launch (RTL) mode (GCS Failsafe).


Will it hurt anything if the manual mode in my transmitter is set to flight mode 6 (high end of the pulse)?

If my transmitter's failsafe function includes switch position, what flight mode should I have it failsafe to?  If it failsafes to Manual mode, will it still RTL if that is the designated failsafe action short/long in MP?


Thanks for your patience


Scott, I guess you must decide which mode you would like to be in if there is a TX problem. Personally I would like the plane to come home and circle above me while I try to sort it out and if I cant, then its not a long walk to collect the bits.

I see on the MP mode setup screen that the lower one (6?) is greyed out and fixed to manual but you can have any (all?) of the others also set to manual. I guess if the RX response is unpredictable then filling the other mode spaces with the one you want will increase your chances of getting what you want.


As far as APM failure is concerned, it would require some level of functionality to output raw servo PWM. You got me thinking about this so I have just tried to simulate an APM glitch by pressing the reset button while in various modes. The system gives you control over the servos (most of them-more about this) after about 3 seconds, and then returns the original mode after about 10sec, however Im not sure how it would cope in the air with zeroing the gyros.


This has reminded me to start another topic. Having 2 aileron channels so that you can have differential is not working properly. After the APM resets I didn’t get the 2nd aileron back until about 12sec had passed.


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