Battery Failsafe RTL

Hi all,
I had some Test and Tuning flights with my quadcopter. There was no Battery low from my Taranis, but from my Pixhawk. Pixhawk entered RTL mode and tried to land about 10m away from the initial arming point which was very near to a brand new car. I had no chance to do anything, every stick input was ingnored. Furthermore the descending speed was set to 0.3m/s but it was much faster. Quad landed hard and flipped over with spinning rotors what caused damages.

  • Is there no chance to takte over when in Battery Failsafe/RTL?
  • The parameters are set right but the Quad descends like a stone. It was a windy day, could that cause such a problem?
  • Any ideas to make Battery Failsafe more safe or gently?

Best regards,

I fly where there are so many trees. So disabled battery FS. Power module is setup correctly and the warning voltage is 3.5 The buzzer will sound and the external LED will flash Yellow.

You can get out of RTL by switching to Stabilize. However, during the landing phase (which is just plain old Land mode) you should have had roll and pitch control.

Since you stated you did not have any control I suspect that Pixhawk lost signal from your radio which triggered the Radio Failsafe.

Post the data flash log for that flight so we can try to figure out what actually happened.

And what do you do when the aircraft is too far away to hear the buzzer or to see the LED?

My Radio Telemetry (Flight Deck) at Taranis showed Battery Failsafe, RTL. I don’t think that it was signal lost, there was no alarm from Taranis and I was very near to my Quad. I’ll download the data flash log and post it. All what really worked was the emergency stop to stop the rotors spinning, but it was too late to rescue them :frowning:

I use Flight Deck and it audibly reports battery percentage and battery critical alerts. Is there any chance you have the sound miss configured in the radio?

No, not at all. My settings are to repeat critical alerts by every 5 seconds…

Sorry, I was very busy the last few days. Here the links to the TLOG and to the BIN.
Maybe someone of you gets an idea, why I could not control any axis during Batt. Failsafe RTL.

You said that your Quad descends like a stone。I think that was the main problem。When the battery voltage is too low,the propeller cannot Provide enough tension。
So maybe your battery warning voltage is too low。

I think this could be the reason. Batt Failsafe was set to 13,2V and 1000mAh reserved and I use a 4S1P 5000mAh.

I have problem to set up my failsafe battery
There is no option to choose
Someone can help me

Any resolution to this issue? No actions visible on the dropdown window for a battery failsafe.

13.2V on a 4S is seriously dead, except perhaps on really old or very low C-count batteries. Every battery is a bit different on the fall-off voltage. What I would recommend is start super conservative, say 14.4V or so, fly it until the FS kicks in. then recharge, and see how much of the mAh you put back. You can slowly lower the FS voltage until you are putting back 75% to 80% of the rated capacity.

Along this line - I would be really interested in seeing a somewhat smarter battery failsafe routine. We fly some long endurance quads using very low C-rated batteries, rated at 6C continuous and 10C burst. They have amazing energy density, but the voltage sags dramatically with current load, so if we use a battery failsafe voltage that is safe for hovering flight, it will be tripped really early during climbs. What I would like to see is a FS voltage level that is a function of the current load, such that lower voltages are OK if the load is high. Perhaps this would complicate things too much for the regular user. What I would probably do is set a failsafe voltage for hover (what we do now) and have an option to add a non-zero slope to account for voltage-sag under load. By default the slope would be zero, but advanced users could add a slope suitable for their system, at their own peril of course.

Hello. Are you solved this problem?

Autopilot estimates the ESR of the battery.

You can switch to using this sag corrected voltage for failsafes by setting BATT_FS_VOLTSRC to 1. Might be worth having a look at logs first to see how good a job its doing of correcting for sag first tho.

Thanks IamPete. I should have known that such a thing existed. Any idea how well it works, in particular for really low-C-rated (high ESR) packs?

Is the corrected voltage logged? If so, where can I find it in the logs? Thanks.

Edit - actually, that parameter doesn’t seem to exist in our 3.5.7-dev version. When did this first show up? I see a reference to 3.6.

I have never needed to play with it myself. its logged as VoltR in the current message. You can also see the calculated resistance as Res.

Looks like you might have to upgrade to latest to get the failsafe options and the logging tho.