Falling out of the sky during loiter

Just did some flight testing in windy weather. After some THR_ACCEL tuning, the copter is quite stable, even under these conditions. Finally tried a loiter in 75m AGL. Wind speed seems to be arround 40 km/h today in this altitude, but the copter hovers very stable with quite some pitch down into the wind.

Suddenly, I see the copter falling, rotating around all axes. I switch to stabilize, fortunately the was quite some air below the copter and I was able to recover. Thereafter, the copter was flying like nothing happened...

Some setup details

 - Arducopter 3.0.1

 - Quad, 6s, props 14x8", about 2,5 kg

 - APM 2.5 powered via separate UBEC (5,0V) on the input side

 - PID tuning completed - very decent flight caracteristics, no tendencies into oscillation even in today's windy conditions

 - compassmot done with current sensor (with great succes - copter loitering very well without any toilet bowling).

I have absolutely no idea what happened. The Tlog reveals, there is no reboot or GPS glitch. The copter is just suddenly starting to roll, pitch and yaw without any input telling him to do so. Any help appreciated...

Regards,

  Holger

2013-07-31 14-04-20.tlog

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Replies

  • 6S and 14 inch props makes me think pancake 24-coil motors. If you couple them with Simonized ESCs you can get into trouble easily.

    I have a Hexa with 24-coil pancakes (AX-4008Q) and a Quad with 12-coil (RcTimer 5010), both with SimonK ESCs. While the Quad flies smooth and tame, the Hex gave me alot of trouble. The motors start desynch-ing and vibrating so bad that not only made me unable to go from 2.8.1 to 2.9.1, but had two hardware failures involving a flyaway prop and a motor shaking itself loose from the screws.

    Some of the desynch went away after I removed the Back-EMF capacitors from the ESCs, but it's still visible when for instance I throttle up hard to end a fast descent. A couple of friends got rid of the issue by switching to K-Force SiLabs-based ESCs running BL_HELI and I've purchased one myself for some bench testing.

  • I just started to experience how to fly quadcopter... During the 2nd flight i had similar issue... mine was falling from 30m and it recovered just 2 meters above the ground.

    And today i crashed 2 times when copter decided to make a flip just few meters above the ground. There was no place to recover from that. :(

  • Developer

    If you have a dataflash log that would be better for this sort of think 'cuz we can compare the NTUN messages Desired roll and Desired Pitch vs the ATT message's actual roll and actual pitch.  There's another wiki here which goes through the most common causes of problems.

  • Scary!

     

    Vibes maybe? Which version of APM is it - 2.5?

This reply was deleted.

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