Pixhawk Issue

A 3DR developer recently tuned my Pixhawk, it flies great, but when he did he also setup my battery failsafe.  Shortly afterwards I was hovering approximately 5 meters away and about 6 feet when the Pixhawk started beeping continuously and started to climb.  Stick inputs had no effect until I switched from Stabilize to Loiter then I was able to gain control for a couple of seconds but then it started beeping again and started to climb so I switched it to AltHold lowered the throttle and let it drop giving it throttle to arrest the decent just before hitting the ground.

The battery was still about 15.2 volts but I thought it might have been related to the battery failsafe since it was set to RTL maybe it was trying to RTL  So I disabled the RTL in battery failsafe and it flew fine with no incidence.  I flew it today and it did the same thing, this time when it started beeping I immediately dropped the throttle and got it on the ground but when it touched down the motor increased and it would not immediately disarm.

Here's the video of the second crash landing, you can here the beeping start about 25 seconds into the video:


The battery was at 15.45 volts and the battery failsafe is disabled.  It also had a flashing yellow LED.  How can I trouble shoot this to determine the cause of this?  How do you download the logs?   I'd share what firmware I'm using but I don't even know how to do that?

Any help would e greatly appreciated.

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  • A couple of things (based on experience.....or lack thereof);

    1) Check the milliamp hours set in your battery monitor, not sure, but I think it will also battery failsafe if you have used available mAh and you have set your battery failsafe. Like if you set it at 5000mAh and then trow on a 10,000 mAh battery, you're stuffed.

    2) Again, could be wrong, but when in failsafe, you have to switch to something else and THEN back to loiter. Once in loiter and you failsafe again, switch to manual and then back to loiter...you may have to do it a number of times.

    3) loiter landings suck. You'll flip it when you try to disarm. drop throttle, let sticks go and switch to manual as soon as you land.

  • Ok, I reviewed the log it matches the flight you were taking.  The battery failsafe was disabled so all you get is the beeping and light noise.  This happens because the battery voltage dropped below 14.2 volts for more than 4 seconds.

    Since failsafe was disabled nothing happens and you land like normal in Loiter mode.  When the copter is about on the ground I see a large Pitch and Roll from you on the stick.  This causes the copter to tip over on its back.

    Other than that it looks like a normal flight.

    PS I would not fly that close to my house in anything other than Alt Hold or Stabilize mode.  I have had several incidents where the GPS drifted because of my house causing the copter to fly off in a strange direction trying to correct for the GPS.

    Did not see that with your flight.

    • Thanks Michael.  

      • Without looking at the logs... I suspect the reason it would not disarm, is because you didn't drop the throttle all the way down, and let the motors go to idle, then disarm. In the video, I don't hear it go to idle speed.

        • That might be the case.  In my haste to get it on the ground, which probably wasn't necessary either since I had disable battery failsafe and it was just letting me know that the voltage had dropped below 14.2V, I probably didn't immediately get the throttle to zero.

          When landing in Loiter the motors always speed up on touchdown and it takes a lot longer to disarm.  I read one of your posts where you mentioned you land in alt_hold, I thought that was odd but I like it much better.


  • I regret using the term fly away in the title of this thread.  It certainly wasn't my intention to debate the issue, I'd just like to know if someone could review the log file and let me know what caused the alarm and what if any parameters I should change to prevent this from happening again.

    • I had a look but nothing is standing out to me, but I only have APM Planner here - I will look with Mission Planner when I get home.

      • Thanks Andy.

        • Chuck -- Just a thought here if no one has mentioned it to you.  Battery voltage with no load and battery voltage under load are not the same.  Your battery probably dropped below your FS trigger setting while under load (flying).  If you measured it or checked it in MP after landing and disconnecting it, it would have shown a higher voltage.  Can be misleading until you understand this.  

          Just trying to be helpful . . .

        • Battery failsafe. You have it set to 14.2v, which is reasonable for a 4s battery and your voltage in flight dropped below this. Your starting volts was 15.5 - which is not a full charge and then the battery drops rapildy to about 14.25 volts where it bounces along until the FS triggers. If the battery was fully charged then junk it and get a new one.

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