I see allot of posts  regarding the APMx in regards to a failsafe. Some Constructive, some not so Constructive....


That's why I was surprised to see that there isn't allot of info out about the failsafe testing mechanism that is in the latest Arducopter Firmware. I have not had my quad up and running for the last month or so, so I can't say when it first appeared... But it sure is a nice feature!

For those of use that aren't familiar with how the failsafe tech feature works, Ill give it a quick rundown.   

It is usually setup on your throttle channel (usually chan 3) and you setup your Transmitter to drop the throttle to a point below the normal range of operation when the signal is lost.

For instance when you calibrate your throttle, it will be something like 1100 on the low side, and 1800 on the high. For the failsafe to activate, the APMx expects to see a number far below that. 975 is the default preset, but you can adjust the threshold yourself if needed. The important thing is that it's well below the normal working range of your TX, so you can't accidentally trigger it.

There are a few different places you can observe this. Just open the mission planner, connect to your APMx and turn on your TX. (Please make sure the copter is not armed, and take precautions) I like to use the Status tab on the Home screen for the mission planner, but you can use the throttle calibration screen as well. Anywhere that you can see the values change when you move the sticks on your radio.

If you have everything on your Transmitter properly setup, then When you turn off your Transmitter, you should see that while the other channels stay within their normal ranges, chan 3 drops to a much lower value....(in my case 900)

Obviously there are more settings on the APMx and your Tx/Rx setup regarding the failsafe feature, but you get the idea.

Anyways When I was setting up the Firmware on my Quad, I found There was a failsafe test feature that I could use to verify that in fact the Failsafe would be triggered when the radio connection was lost. So for those that have not ran through the setup in awhile, check it out! It's a nice feature.

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Does this pre-empt auto flight? For example if a waypoint in your mission is outside radio range, does the mission stop? Or does failsafe only kick in if you are not in Auto mode?

This is copy and past from the wiki under failsafe:

There are two options for failsafe. If you are in Auto and prefer to continue your mission, the parameter THR_FS_ACTION should be set to 1. If you prefer to have the copter RTL even if it is flying under autopilot, set THR_FS_ACTION to 2.

I wasn't really sure how to go about setting this up on my TX and was a bit wary to try it in case it cause a major crash or total loss of control of the copter. So which TX are you using and can you please give a little more instruction how to set this up in the TX?

I'm not really an expert on this, But the first thing I would do is turn your TX on and connect to the APM Via USB. Click on the status tab and find the 4 channels controlled by your sticks. You should see the values changing as you move the corresponding controls. After that you can turn of your TX and see what happens...

If your watching on the status tab (or wherever) your going to see Channel 3 take a dive, hopefully to well below 975. (mine went to 900)

You may find the TX side of the failsafe is already working.....If it's not I would go through your TX settings and look for anything labeled failsafe.

I'm Running a Turnigy 9x Radio (which depending on the firmware has know failsafe issues)

Of course please make sure that your battery is not plugged in and/or the blades are off.

Actually converted my Er9x to Frsky, and the way they have it setup is that after Binding you can set all your controls to what you want them to go to in case of a Fail-safe issue, so you have to temporarily configure your TX to go down under 975, put the rest of the controls to middle. I was thinking that I could have just set the radio to switch into RTL via switch settings, but after thinking about it Id rather have the APM deal with Failsafe (which it already does) rather then trying to find another solution.

Thanks for this explaining. For a n00b like me, there has been always the question which part should handle failsave. FrSky and Modeswitch or FrSky/Throttle and APM. So i think your solution is more flexible, because you could change things in Mission Planner. The question i still have is timing. FrSky TX triggers to set default (middle) positions, throttle, gear, mode switch etc. So in theory, could there randomly be a short moment before the APM detacts the lower throttle value, after the mode switch triggers to its middle position?

I've just tested this a couple of days ago on my quad. I've set failsafe to RTL when throttle goes below 975. I was a little nervous when trying it out, but flew to about 100m height and 100m away from me and switched off my radio (Futabe 6EX) and low and behold it return to me and landed at my feet :) job done

It is nice to see it come home isn't it?

And yes, If your running telemetry you have more control with a craft in RTL and no transmitter to fight it, then with a failsafe effectively overriding anything you try to do. I'm not quit sure what you mean by there being a moment between. What ive seen is that once the transmitter goes offline it continues on auto until RTL kick's in and brings her home. I would have the frsky setup like u said in the middle with half throttle. I have mine set currently on a full one way ticket all the way home, without the option to regain control. It's normally set for you to be able to regain control when it comes back in range...but were so far removed from the craft that it could seem to use like were losing control rather then reaching the limits of our TX. Actually that's another reason why I have my laptop set to call out the modes when there switched.....It's nice to have audio confirmation on exactly what your UAV is doing!

you can verify that Failsafe is working correctly by using the .log files.

See my post titled:

Example of using .log text file to verify Failsafe Action which is saved in Mission Planner section of forum.


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