After nearly two years of putting around with no nasty surprises my heavy Hex, "The Witch" has been behaving badly and yesterday gave me a fright.

A couple of weeks ago I moved up to 3.1 from 3.0.1 and in test flights noticed that there seems to be some sort of coupling going on between yaw commands and pitch/roll, because whenever the ship is in Loiter mode and holding position and even a gentle smallish (20-30 degree) Yaw input is commanded there is significant lateral movement. I posted a question about this on the new Arducopter forum and have gotten zero support there, so yesterday I decided to make a video of the behavior and to post it here. There's still no video because of the below event, but I would sure appreciate some help with that.

So, as I was preparing to launch yesterday with the intention of making that video, here's what happened (clip is in HD on Youtube).

I was peering down at the indicator lights while arming to make sure I had solid blue (I now hate even more not being able to see those lights at a safe distance). That was a nasty scare (see Oliver jump!)  when the Witch abruptly spooled up under my face, with no input from me and zero control. Neither the spool-up nor the shutdown was commanded by my Tx. Flight Mode was Stabilize.

As is seen from the log (attached, and a screen shot at end of video) the Hex thought it was landing. The only failsafe set to "Land" was GPS loss. One other failsafe was enabled, Throttle (to RTL). Geofence was also enabled with 100 meter distances and RTL action."Check on Arming" was disabled.

Location of incident was our AMA field, very GPS friendly with no history at all of glitches, multipathing, etc., as it's far from buildings etc.

Firmware was 3.0.1, I had dialed back to that from 3.1 a couple of days ago while hunting for the source of the Yaw problem (it made no difference). APM 2.6 with Ublox GPS and compass both on stalks, excellent vibration numbers, never crashed, no question of inadequate power.

Log file attached.

I'm hearing that this may not be the only incident of its kind recently. I'm pretty unhappy about it, and until I at least find out the cause I consider flying this ship, in which I have a lot of time and money invested, rather risky. I'm hoping for practical advice here to prevent a recurrence. Meanwhile I'm bumping the firmware back up to 3.1 and disabling all the failsafes and Geofence. 

Thanks for looking!


2014-01-04 18-11 6.log

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  • I agree with those who posted about LEDs. I use VERY bright LEDs purchased from ebay. They are using the LED feature as R.L. suggests. One Red and one Blue. They are like head lights they are so bright and easily light up areas on my home walls over 7' away at night. You don't want to look directly into them. They are great at the angle on my quad and perfect for indicating status from a good distance.

    I like the motor spin - Very Much! I am able to give a verbal to others around what my actions are. The buzzer sounds to alert that actions are beginning. The motors spin Very Slow with the exterior indicator LEDs are on. EVERYONE now knows not to just wander through. This works even for the Deaf just not the ....

  • Might I suggest adding external blue and red LEDs as described somewhere in the Wiki? I had the same difficulties of having to poke my nose in too close to see GPS and arming status. Very uncomfortable feeling. Ordered some extremely bright blue and red LEDs from and now I can see those things in sunlight from 50 feet away. Between the LEDs and resistors it cost less than $1 each. You can use just plain Radio Shack LEDs, but I wanted something very bright (and didn't exceed the APM's current limits).

  • Hi All,

    In response to Andke, Oliver is meticulous in following instructions, loading firmware and executing tuning and calibration procedures and he is safety conscious to a fault. He also flies 450 sized helicopters.

    Prior to 3.1 you actually needed to stand in proximity of your copter to be able to establish GPS lock among other things.

    Even with 3.1 unless you have your failsafes set up to not allow takeoff without GPS lock it is still very difficult to know the APM's status without observing it directly.

    Unless you have telemetry of course, but only a small percentage of our flyers have and use telemetry so it is not a normal or reasonable presumption of it's presence and Oliver does not have it.

    I do think that your responses have exposed an Achilles heel for our failsafe system and I think that the appraisal that tuning out the motor spin feature with sub trim is not the proper way to do so was correct.

    There are arguments on both sides regarding the value of motor spin on armed and the fact is that different copters idle spin is drastically different from copter to copter (really slow to non-existent on some and entirely too fast on others).

    From looking at Olivers logs it can be readily gathered that for whatever reason a failsafe was generated and that his preset "Land" failsafe was executed and that already being on the ground it displayed some bizzare behavior attempting to do so.

    If you look closely at the copter trying to spin up you will notice on his hex 3 motors spinning up (every other one) and the others not.

    Clearly it was attempting a yaw (presumably to align it's land direction) and it actually seems to have used the internal on the ground turn off the motors feature (which is part of the Land mode) to turn off the motors completely. (This is done by determining that the copter has not moved more than 20 centimeters vertically in (I believe) 2 seconds.

    So in the end the I have landed autoturn off saved the day.

    It would probably be better if we also had a (I have not taken off yet) flag as well that was cleared immediately after take off.

    That would probably solve this sort of problem.

  • For those too lazy or computer-challenged to view the video of this incident, the text in my earlier post apparently does not make it clear enough, in spite of identifying the firmware version,  that this incident is not the now normal light motor-turning-on-arming feature (which I have disabled via my Tx sub-trim in any event - a horrible feature, IMHO),

  • The really scary part, is to see how people ignore release notes, and uncritically load any software offered.
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