Document all failsafes about px4-user_guide

[hamishwillee]

Thanks @MaEtUgR Yes, I'll close this. Thanks for the tip re "fixes". I knew there was some magic, but hadn't realised exactly what it was!

[hamishwillee]

Also include this info (from @barzanisar )

You can also directly configure the most common failsafe actions e.g. what to do in case of low battery, RC loss, Data link loss (between vehicle and QGC) and geofence breach in the QGC's Vehicle Setup > Safety. Additionally, the Safety tab provides the commonly used Return to Home and Land Mode Settings which are also important for mission mode. Configuring these settings is an easier alternative to changing the corresponding parameters in the Parameters tab.

[hamishwillee]

See mavlink/qgc-user-guide#138 for Battery clarification discussion

[hamishwillee]

There is a question in mavlink/qgc-user-guide#138

Critical and emergency battery thresholds parameters state "This threshold commonly will trigger RTL." It would be clearer if it states that it will follow the failsafe selected in the Safety setup. Or am I wrong and there is some override of the desired failsafe, and it goes to RTL in certain instances?

The way this works is that there are 2 battery thresholds (docs indicate "the common action at threshold" as shown):

• BAT_EMERGEN_THR - Landing
• BAT_CRIT_THR - RTL

However the actual action is defined in COM_LOW_BAT_ACT and defaults to warning - you get a warning at both thresholds. You can also select RTL or Land (which will obviously be invoked whichever threshold is reached first). Last of all you can select to RTL for critical and Land for emergency.

The problem is that the docs indicate that you will commonly see the last option, while the actual response defaults to just warning on both thresholds.

@MaEtUgR IMO EITHER the default action should change to 3 OR the text for the BAT_EMERGEN_THR and BAT_CRIT_THR should change from "This threshold commonly will trigger RTL" to "This threshold will trigger warning, RTL or Land, depending on the value of COM_LOW_BAT_ACT."

[hamishwillee]

This will be fixed by #212

[MaEtUgR]

@hamishwillee I think the default is to do no action because if someone builds a prototype vehicle, it doesn't fly properly in every mode yet and/or the battery parameters aren't configured correctly it could automatically do something unsafe (I've experienced this case before). Hence it was probably decided to be better if the vehicle fully obeys on remote input by default.

As you suggest I think the documentation should say it warns and can be configured to react automatically.

[MaEtUgR]

@hamishwillee Are all the listed conecrns now fixed with #212 ?
Then we could close this issue...

EDIT:
Hint: If you write e.g. "fixes #205" in the initial description of your pull request then the issue gets closed automatically as soon as the pr is merged, see https://help.github.com/articles/closing-issues-using-keywords/