I too am trying to get to the bottom of a failsafe issue. A couple of weeks ago I deliberately switched of my TX to see if the failsafe would work. Unfortunately my quad just fell out of the sky and did not ReturnToBase which was the failsafe flight mode setting. My setup is slightly different in that I am using a Revo and not a CC3D. I am using a FrSky X4R-SB receiver which is connected to the main port of the Revo and configured for S.Bus.
I've tried to set up the failsafe settings on my X4R-SB using both the Taranis TX and also using the F/S on the RX. In both cases, I've set throttle, yaw, pitch and roll to neutral positions, and my flight mode switch to 6 which is the ReturnToBase flight mode. In both cases, when I switch of the TX, all remote control inputs go to their maximum values, in my case 1811. For the flight mode this is OK because it is position 6, ReturnToBase, so should hopefully do this on loss of signal from the transmitter. However, that didn't appear to be the case a couple of weeks back.
I should add to this that the ReturnToBase does actually work OK. When I switch my TX to position 6 (ReturnToBase flight mode) my quadcopter does return to where it took off, a set hight above ground level.
I've also tried setting the RX to no pulses on loss of signal (not sure what this means for S.Bus), but again, no different from before when the TX is switched off.
Another test I carried out a short while ago was to disconnect the S.Bus line from the Revo when the TX is on. The effect was the same, all channels on the 'Remote Control Input' tab go to maximum (i.e. 1811) despite the failsafe setting on the 'Failsafe Settings' tab being neutral, apart from the throttle which is set to -100%. Even changing the failsafe flight mode to a value other than position 6 does not seem to get reflected when S.Bus is disconnected.
Firstly, I am not convinced my RX is doing what it is supposed to on S.Bus when supposidely configured to send failsafe channel values to the Revo. I need to hook up a logic analyser to explore this further.
Secondly, I am not convinced the failsafe is working on the Revo for the S.Bus input. Probably failsafe on Revo does work OK for other receiver configuration modes such PWM and PPM, but I haven't tried, but I am assuming others have and use without problem.
I am using a version of 'next' that I compile the beginning of April. Looking to recompile and try with a later version of 'next' once the compile issue has been resolved, reported in a different thread.
Is anyone else using S.Bus and failsafe without issue? If so, any clues as to what I may be doing wrong?