Well, one of the shittiest and most destructive things that could happen to a UAV happened to me today. Accidental low-battery LAND failsafe set my 3DR Y6 down... into a pool. I retrieved it immediately and disconnected the battery. Now I'll wait for a few days for it to dry out before doing some system tests, but I'm curious what your expectations for system function will be at this point. Crappy? I think so. It was smoking when i pulled it from the water. Oy. 

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Don't use any battery failsafe because of these reasons...

RTL: you might be under trees or there may be other rc aircraft in the area
Land: you might be over water or a person or a house

Instead just use a simple $5 lipo battery alarm set to alarm at 3.6v per cell.

Then if you get the alarm you can then switch to RTL,land, or manually land depending on
your situation.
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Incorrect.  All you need to do is change modes.  Any user input overrides automated mode changes.  You can switch it into anything you want after the failsafe kicks in.

In retrospect, I'm not entirely sure that the land failsafe had been triggered. Just a day before, I had checked the battery failsafe settings in APM Planner. The available range for critical voltage ranged from 0 to 66,000 something. I figured this was a bug, and manually entered a value of 9 into the settings.


Maybe 9V was too low, and i didn't have enough power to control the UAV? I don't recall what the amperage threshold I used was, but that may have been set too low also.  


Ok, that's another big problem.  Lets say that setting really is 9 volts.  That is flatline dead.  Way too late for a failsafe.  If you are using a 3S battery, that is only 3 volts per cell (dead).  It will fall out of sky long before you reach that point.

The failsafe voltage is properly presented in volts in the mission planner failsafe settings screen.  Again assuming you're using a 3S battery, something more like 10.6 or 10.7 would be appropriate.  For a 4S battery, more like 14.2.  But you would be best served looking at your log files to see where the voltage is with about 3 minutes of flying time left.  That way the failsafe has time to execute.

These things can happen and unfortunately are unpleasant.
But we must also pay close attention to the timer on your tx, you did set correctly?
ou should not rely solely on the battery failsafe, especially if it's no set to RTL, and f
lying above a pool with the battery failsafe set to LAND is not a very reasonable thing.
By relying on automatic failsafe and related thing you must first know them well.
If you're using now battery failsafe sets the value of not less than 10.5V for 3S Lipo, you need to consider that if the drone is far takes time to return to the home and land, and often this process can take minutes.
Imho the battery failsafe default must be "disabled", the users who must inquire about this feature and how to enable it and decide in what way, or the code should figure out how many LiPo cells you're using and set an appropriate voltage value for them.
My two cents...


By the way, I take full responsibility for the crash, and I'm grateful that the only damage that was done was to my UAV, and not to anyone else's person or property. It's a strong lesson to me, and hopefully to everyone else reading, that not knowing your device and it's settings inside and out puts people around you at risk. Learn from my mistake.


Be informed. Be thorough. Be patient. Be responsible.

Hi Ben, i'm not talking about responsibility, but knowledge of the vehicle and of the parameters.
I understand that many things can not be very intuitive, but a good starting point is read the wiki very well before you fly your own drone, whatever it is.
I've thousands flights with this system and I never went into the failsafe action for low battery, and always landed before it triggers.
The battery failsafe I see it as an emergency, not as an automatic on which to rely on.
Use a good LiPo and the tx timer set appropriately... good luck!

Cheers, Marco

Not a theory.   I fly mine into the battery failsafe almost every time, and I switch to a different mode, take over, and land it myself.  Never once has it gotten "suck" on the failsafe mode.

My concern with the Failsafe enable/disable options is within the Mission Planner.  I have requested a consideration to foolproof the placement of the disable/enable by placing them next to each failsafe.  I had a mishap last week because I thought I had the Low Voltage failsafe disabled while flying in a woods.  I had the Failsafe RTL activate at the low voltage setting.  I didn't have time for the mode to change because I was below the tree branches.  Even though I had 15 to 20 feet of clearance, it was not enough time to cancel the RTL mode (- I tried).  After the crash, I went to the advanced parameters and confirmed the RTL was enabled.

I always spend more time checking my multicopters and failsafe options than I seem to fly.  Do I need to confirm my  Mandatory - Failsafe selection by going to the Advanced Parameters every time? :)

The placement/layout of the enable/disable failsafe options are not organized in a foolproof manner.  They were better in previous versions.  - Refer to the WiKi.  It still shows an older version.  

Even though my concern is an enable/disable issue, I keep asking my self if the default would have been better if LAND was enabled.  I still would have preferred disabling the low voltage failsafe, but at least the LAND would have saved me $40 of damage.  Regarding a pool, I wouldn't want the LAND option either.  



I always complete my flights before the low voltage alarm goes off.  This was the first time it went off.  The quad was only five feet away from the launch pad so it makes me really disappointed that I didn't confirm my Low Voltage failsafe setting in the Advanced parameters.  

I've been away from the forum for many months, but I recall that the RTL won't be armed until the copter is 10M from it's origin.

That could, of course, have changed.


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