Power Quad Build - Loiter Issues



APM 2.6 running Firmware Version 3.0.1

Motors: T-Motor MT3520-11 400KV

Props: 13 x 4.7 APC Slow Fly

ESCs: Pheonix Edge Lite 50AMP

Radio: Spektrum DX8



As you can see in the video above, everything runs smoothly in Stabilize Mode. We get no "wobbles" when dropping altitude quickly and the copter responds to the operator instructions as expected (forward, backward, left, right, yaw left, yaw right) however as soon as loiter mode is engaged, we end up with a spastic quad.


If anyone can help us identify the issues that are going on here we would greatly appreciate it. Please find the log files for this flight as well as the parameter set attached to this post.


Thanks in advance for all the help!

2013-10-24 11-33 24.log

2013-10-24 11-33 24.log.gpx


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  • So after further testing today, with hardly any wind we have discovered that the Loiter Mode is quite stable but as soon as we get some wind, it goes to hell. Also, when flying the copter laterally in Loiter, we are losing altitude. We have put black electric tape over the APM since someone had suggested that we keep light from getting to the Barometer but we are not sure that has helped at all. Please see this video to see what we are talking about:


    Anyone have any suggestions as to how to stabilize the quad while it is in Loiter Mode? Seems that we have most of our problems in wind with regards to instability and we have no idea why we are losing so much altitude while moving latterly (especially in the wind). Attached are the log files and the .kml.


    Thanks in advance for all the help!


    2013-10-25 15-17 26.log

    2013-10-25 15-17 26.log.gpx

    2013-10-25 15-17 26.kmz

  • I posed a couple aof weeks ago a very similar situation which resulted in the crash and destruction of my 3DR quad. I notice since then that this is about the fifth or sixth post on the same basic issue - the quad going nuts when switching mode. For me it was when it started its' descent on RTL.

    I had a similar but not catastrophic event on landing about a week earlier.

    This all happened after installing 3.0.1 firmware

    I had flown this copter successfully for about 8 months successfully without incedent.

    Could there be a firmware issue?


  • From the log file, I can see two modes - stabilize and loiter.

    • One clear signal is the APM drop the satellite count from nice 14 to 8 all of a sudden when the mode to Loiter is engaged and takes a few seconds to regain back the sat count - Hdop (effectiveness of position hold for GPS) rises to above 4 (very bad - should be below 2 for decent GPS hold). Since loiter relies on GPS mainly, lack of GPS leads to the resulting performance. This could have been due to on-board interference (possible).


              There is a sudden altitude drop (source code uses accelerometer + GPS velocity for position accuracy - computing speed in x,y directions), as I understand.

    • There is a sudden change in input throttle (i.e. you may have brought down throttle stick OR you engaged throttle cut switch on your Txm resulting in sudden drop of output throttle (i.e. reaction of copter's altitude). It just did what was told to do or maybe loss of Txm (however, no error was found in the log - so seems Ok).


    Btw, off topic but curious to know the net weight, battery used and flight time :) ?

    @I have edited the above after initial post.

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