Sudden sharp voltage drop off mid flight

Hi all

We have a DJI s1000 Octocopter with a genuine cube orange, Mauch PL-200 sensor and Tattu 22000mAh 6S battery

I have just began flying it and getting a feel for such a large craft, and doing some gentle tuning, though ive input PIDs from another pixhawk s1000 and it flys not too bad as is.

the first long flight i conducted went very well, the voltage display was logical and i tuned and flew down to 10% soc, admittedly i had began landing at around 15% but decided my landing spot was less than ideal so moved on to a better spot.

the second flight, again everything was great and i spent a good amount of time flying figure 8s and moving up and down in altitude, until at around 30% i suddenly got a battery critical and bad battery error. the craft began increasing in altitude due to smart RTL but given the stark nature of the warnings i took back control and brought it down fairly quickly, bounced on the gear and broke a couple props but other than that no major damage. it didn’t seem to fly very well on the way down.

im pretty new to ardupilot/pixhawk and drones of this caliber and am hoping you more skilled people can help me nail down just what went wrong. ive attached both flight files and i note that for the same battery % the voltage is different. for the crash flight, were i watching the volts and not the % i would have seen the issue before the warnings kicked in but hindsight is 20/20.

the battery was pretty warm but i am unsure if this is due to the flight issue or the much higher drain than it should have seen

Logs available here - https://file.io/cOtErL0CLQox

Cheers!

i figured it out but will leave this here incase it helps others

the percentage remaining resets to 100% each time arming occurs despite the state of the battery. i will set up appropriate safety limits and fly with an eye on voltage not percentage.

For 6S lipo set these:

BATT_ARM_VOLT,22.10
BATT_CRT_VOLT,21.00
BATT_LOW_VOLT,21.60
MOT_BAT_VOLT_MAX,25.20
MOT_BAT_VOLT_MIN,19.80
BATT_FS_CRT_ACT,1
BATT_FS_LOW_ACT,2
It’s all in the Initial Parameters section of MissionPlanner.

Probably a good idea to set FENCE_ENABLE,1 and check the other Fence params
Also consider setting and testing your RTL params and the Land params
LAND_ALT_LOW,700
LAND_SPEED,40
LAND_SPEED_HIGH,140
(just my own here, test and set your values)

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The capacity reset happens not on every arming, but on every power up. These are different. In your case, you probably shut down the copter after each landing, and if such, this is the expected behaviour. However, multiple flights without disconnecting the power from the flight controller will not reset the current drawn.

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