Hello everyone. I hope you are all well.

We took our octocopter out for it's first flight test today after having done some modifications since it's maiden flight.. We have gone from 4S batteries to 6S, installed an AttoPilot 180A current/voltage sensor (thanks to Bill for helping with that), flashed a new firmware onto the Frsky system so we can run combined ppm, and a few other little things.
We reset the APM 2.5 in order to clear the old settings and start fresh. Went through all the various initial flight calibrations etc. 
We used the auto-trim mode and straight out of the box the octo was flying pretty well in stabilize mode. We then went into Loiter mode and that's when we came across a big and very frightening issue..

As soon as we went into Loiter mode the octo veered briefly to the right before heading back to the left quite rapidly. We went back into stabilize mode straight away as in was in danger of crashing.
We tested loiter mode a few more times to try to get an idea of exactly what the octo was trying to do / where it was trying to fly through. One flight we were game enough to leave in in loiter mode for approximately 5-10secs and we noticed it started to circle in an anti-clockwise direction. At that point it clicked it may be the "toilet bowl" effect I have read a little about?

We ran through another manual compass calibration and tried loiter mode again with the same results, the octo wanting to fly away on its own.

After weeks of trying to convince my business partner to stick with the APM 2.5 and allow enough time to tune it correctly, the issues with loiter mode today may be the factor that has him replace it with a Naza which I do not want to do. So I would love some help in order to resolve the issue. We are running the latest firmware 3.0.1.

Does the position of the GPS unit affect loiter mode at all? Where we have the GPS unit at the moment, it is not blocked directly above by the batteries but they are above and to either side of it. Would this be causing any problems? Should we relocate the GPS unit and raise it?  If so would anyone happen to know where we something to raise it and secure it with, similar to the Naza systems GPS?

I have attached logs for the flights. We are getting great flight times although we are not carrying any gimbal or camera weight yet. Our last flight was 20mins off 2 x 8000min batteries, and that was general flying not just hovering, so we are really happy with the flight time and the APM performance in general.

Any suggestions / help to resolve to loiter problem would be fantastic. I am happy to go through any steps needed to fix it.

Thanks very much,

2013-08-28 14-35 37.log

2013-08-28 14-36 38.log

2013-08-28 14-37 39.log

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  • I'm probably very late here, but I had similar problems and fixed them by enabling the "COMPASS_LEARN" feature, which calibrates the compass by using GPS data. Give it a try if you haven't yet.

  • My first attempt would be to raise the GPS above everything else including propellers, then do compassmot and check that the value reported is under 30%, if not either relocate apm or try with external compass.

  • Developer

    Compass interference is more sensitive in AC 3.x. The best option and especially with a powerful machine you have is to use an external magnetometer. The newer APM2.6 does not even have a compass on board but relies on an external compass. The new GPS unit has a built in compass, which is supplied with the APM2.6.

    You can make your loiter much better with a software solution by doing a compassmot, and gives you an idea on the level of interference.

    see http://copter.ardupilot.com/wiki/ac_compasssetupupadvanced/

    for adding an external compass

    see http://copter.ardupilot.com/wiki/common-external-magnetometer-for-i...

    You can install this part http://store.3drobotics.com/products/hmc5883l-triple-axis-magnetometer

    or the combined GPS/COMPASS

    see http://store.3drobotics.com/products/3dr-gps-ublox-with-compass

     (note: remember you need to break the trace for the ext compass to work, and you need to mount the ext compass ot combined GPS/compass as far away from the PDB as possible ie.5-10cm)

    The end benefit is loiter is much better in AC 3.x, slight upgrades with a measurable outcome.

    PS: you should have your GPS elevated above any transmitting antenna on your platform, to reduce stray signals interfering with the sensitivity of the GPS receiver)

  • And the final flight log attached. Cheers.

    2013-08-28 14-42 40.log

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