Feature request: Universal Rx failsafe

Hi all, I don’t know if this is the place for feature requests, but here we go…

I’d like to request a feature where APM engages a failsafe if it hasn’t detected a change on a certain channel for more than 1 second (or whatever…)

The idea is this*:
I just finished a Pixhawk quad, and I’m using a Turnigy 9x transmitter. Stock module and Rx, but Er9x flashed.

I’d like to have an Rz failsafe, but the Turnigy doesn’t provide that option. The Rx just keeps outputting whatever the last signal was. This worries me, since the quad would then just fly away in whatever direction it was going until the battery died…

I don’t want to upgrade to FrSky, just for the failsafe feature… What I can do, however, is set up the transmitter such that one of the channels outputs a periodic signal, say 1000 ms one second, 2000ms the next, repeating forever.

Then if radio contact is lost, it can be detected by the flight controller, by the fact that a specific channel is no longer periodically switching.

It doesn’t need to be a separate channel, either. It could be implemented on the mode channel, or some switch channel. Say, channel 7 is setup as a switch (high/low). You could set high = 1800, low = 1200, and then put a periodic signal of about +/-100ms on top of that.

The output would be:
high: 1700-1900-1700-1900-1700-1900-etc…
low: 1100-1300-1100-1300-1100-1300-etc…

If the periodic oscillation stops at the Rx side, the flight controller can detect that radio contact has been lost, and engage failsafe mode.

Anyway, I this this type of failsafe detection would be a great feature to have in 3.2

*After googling, I was slightly disappointed to learn that I wasn’t the first to think of this… I found the same idea here: openrcforums.com/forum/viewtopic.php?f=35&t=1054

There must be a way to set your failsafe. What receiver specifically are you using?

I have worked with the stock turnigy 9x8c-v2 receiver (aka Flysky v2) in a homebrew project. It’s not programmable, upon losing signal it maintains output on all channels except channel three which ceases outputting pwm entirely.

Failsafe may be implemented by checking only channel three for PWM. I think this would require quite some changes to APM, and probably a bunch more failsafe options to need setting up.

I have upgraded to frsky for my good stuff, but the turnigy has solid performance for the price.

A dev should evaluate the feasibility of this.


Can you give me a telemetry log in which you toggle your transmitter on and off?

what are you talking about?
turnigy 9x v2 gives no output after few seconds that you powered the transmitter off.
you can test this by connecting a esc with motor directly to the turnigy receiver.
if you connect to apm i see now that it stays with last known signal frequency.
i’m still tring to understand how to solve the problem and few minutes ago i found this: copter.ardupilot.com/wiki/common … tmega32u2/

EDIT: i was not clear on my previous post. Anyway I found the solution, you can maintain your radio and still use the failsafe functionality.
it is all explained in this other thread:

Gaucho: Thanks for your info! Like you said, I was confused by mission planner’s Failsafe screen, which shows all signals remaining at their last known value after I shut off the transmitter. I hooked the receiver up to a scope, and it does indeed stop outputting PWM after signal loss.

I think this is an issue in the mission planner RC signal display. It’s really confusing to see the signal after the TX is switched off, especially on the F/S setup screen.

I set up radio failsafe according to (copter.ardupilot.com/wiki/throttle-failsafe/), and I confirmed that F/S is working correctly now (Switch to RTL mode on signal loss). Thanks!

(I was on vacation for the last month, so sorry for my late reply.)