Mini 2 flyaway

[maccboy]

Hi

I've had my Mini 2 for a few years - so I know what I'm doing!
I put it up yesterday and got a warning about a battery issue. When I tried to land it, it just drifted away. The joysticks had no effect and the drone just kept drifting in the wind. I was hoping that someone here could find out what the cause was, because I'm rather worried about flying it again, in case the same thing happens.
I've attached the TXT file.
Cheers. Andy.

 

[slup]

No... this wasn't a flyaway at all.

Instead it probably was a flight conducted with a battery that had been laying for a long time & self discharged.

The flight started with the battery at 52% (but that was totally wrong as the BMS in the battery hadn't counted in the self discharge)

This was the messages you got... note that the first battery power related message comes in already 4s into the flight.



Looking at the battery voltages per cell clearly shows the mismatch between the percentage & the voltages... have placed the chartmarker at 32,8s... there the BMS think's the percentage is 49%, but both cells are already below 3V.

At about 70s into the flight the BMS realizes that the percentage calculation is wrong... & the percentage drops fast down to 0%.

At 80s the forced low battery voltage auto landing kicks in...



That the AC didn't responded to the stick commands was due to the low battery voltage... already at 4s into the flight you got a "Battery power restricted. Aircraft performance decreased to ensure flight safety" message, so your Mini 2 was powerless & couldn't fight the rather strong wind & drifted instead.

Here the wind speeds...



So this was a clear blow away coming in as a side effect from flying with a bad battery.

 

[AeroJ]

You can upload that at Phantomhelp.com if you'd like to go through it yourself, but the TLDR is as follows:

1. Flight started in GPS mode with 17 satellites, and normal GPS mode. That is enough to take off with, but not enough to be sure GPS positioning will hold if some drop out...

2. 2.6 seconds in your battery sagged to fairly worrying levels, and was flagged by the software as suspect.

3. 4 seconds in, and that battery is now down to 3.08v per cell (almost minimum), and power is restricted to UAV.

4. After 10 seconds the battery recovered (somewhat) just in time for a Weak Satellite positioning warning !

5. 13 seconds, and the battery returns to worrying sag level.

6. By 1m 18 seconds your satellite positioning had stabilised but battery was now at critical level.

7. From 1:20 it commences forced landing due to impending battery fail.

8. 1:54 UAV is force landed, with battery pack unbalanced and 1 cell at critical level even unloaded.

So you went drifty in very high wind when you lost GPS positioning (even though it says it returned), and your battery pretty much died almost as soon as you left the ground, putting the aircraft in restricted speed mode, further affecting your ability to fight wind, which probably overpowered your UAV giving the appearance of drift.

I would monitor that pack very carefully on the recharge and be prepared to bin it if the imbalance remains, it swells or changes shape in any way at all, or has difficulty charging.

 

[maccboy]

Thanks for your replies. That's really interesting. Is there any way to make sure this doesn't happen again? Do I need to condition the batteries somehow, or discharge them and start again? Thanks again.

 

[slup]

Thanks for your replies. That's really interesting. Is there any way to make sure this doesn't happen again? Do I need to condition the batteries somehow, or discharge them and start again? Thanks again.

Never ever start a flight with a battery partly charged that also have been laying around for a long time, always charge your batteries before you fly.

 

[AeroJ]

Is there any way to make sure this doesn't happen again?

Yep, don't leave batteries lying doing nothing for months at a time. Charge them periodically, and run them through a cycle or 2 to keep them in decent condition.

Also, when you first take off, just hover a few feet above the ground for 1 minute while you wait for any warning messages and can monitor live battery voltage to make sure it is a) balanced and b) not dropping wildly.