Loiter Not Work

Hey folks,

I have an APM2.5 running on a SK450 with whatever the latest version of arducopter firmware is. Using a ublox gps and 900mhz radio telemetry modules with 2.4 for rc control.

In stabilize mode the quad works great. I fly up to about 5m altitude switch on loiter and then it behaves erratically, flies sideways, down tips and crashes. Done this twice.

I though loiter was meant to 'lock' the quad in position and only move with inputs from me.

Anyone got any ideas - i think the hardware - escs, motors, all the acceloromters, gyros, gps etc seem to be working fine in stabliize - so it must be something else?

Thanks so much for any help.

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  • There is something significantly more going on here than vibrations. I have vibrations only slightly lower than yours on one of my SK-450's that has 160+ autonomous hours of flight on it, without a single incident. Can you post both the dataflash log and the mission planner log? There also seems to be something happening on your vibration logs that is causing significant disruptions in operation, specifically at the points we see ERR:GPS-2 and ERR: GPS-0. Note how the logs do not show any vibrations for nearly 30 seconds after these points. Without logs, it's not entirely possible to see what's going on. It could even be a 3.3v regulator problem. If your altitude is swinging massively on the ground, do yourself a favor. Unplug your GPS, make sure your compass is still plugged in though, and boot the APM. I wouldn't recommend flying like this, just boot it. Set it on the floor and arm it. KEEP IT IN MANUAL MODE and immediately disarm it, do not fly. This will set the home altitude. Pick it up and place it on a table, and watch the altitude for any harsh fluctuations. You should see the altitude move to around the height of the table. Post that log here :) 

    Another thing to try is to plug your APM into your computer VIA USB, do not plug in the main flight batteries, and go to terminal in the Mission Planner. Then, go to tests and test the IMU with the copter sitting still. If you can post either a screen capture of that or copy it into a text file, that would be massively helpful.

    • Hi Austin, I was thinking those pauses where there is very little vibration recorded is when I had landed the quad on the ground – before taking off for hover again?

      • Upon reviewing your logs, I think it's most likely you landed during those periods ;) That still does not explain your GPS errors.


        If you look at the reported barometer altitude in the dataflash logs, something is incredibly off. Note that the GPS altitude, while not used in the current firmware (that I know of) holds nice consistent altitude readings while your barometer reads massive jumps ranging from -750 to +1250. The blue line represents the composite altitude going into the IMU controller that's suppose to compensate for drift and make sure the IMU isn't off from the actual altitude by large values. Out of curiosity, do you have your barometer protected from sunlight? I cannot think of any way this behavior could happen under normal circumstances. Also, can you enable all the logging functions? I can't see the calculated INS altitude ;P I think something is wrong with your barometer on a hardware level. Run tests on the barometer and, just to make sure, the IMU in the terminal, that should give some clarity as to what exactly is going on with your board. Keep us updated!

        • Hello again,

          I have put the APM in its black enclosure, it has black foam over the barometer and is nice and sealed up. I attempted to graph the same variables you graphed above for comparison (attached below). It appears that the altitude is now working correctly?


          Why is the GPS altitude so high whilst the relative and barometer altitudes are virtually identical? Wouldn't the relative be based on GPS+barometer? I think mabye the GPS altitude is above sea level whilst the relative altitude is above ground level (takeoff spot)?

          Attached below is also the log file from the most recent flight, once the barometer was shielded. If you could be so kind and have a look, is there any other variables that i need to fix before attempting altitude hold then loiter?

          Thanks so much.

          barometer shielded.jpg

          2014-04-19 13-28-48.log

          • UPDATE: Today i tested altitude hold mode and i love it! I am impressed with the way it works. However when i fly a bit more aggressively it will sometimes loose height as if it is not aggressively enough trying to maintain its altitude, also sometimes the quad will climb a couple of meters very slowly. I am sure there is a parameter for this altitude aggressiveness - if someone can point me in the right direction - also how much should i change it by/whats the scale?

            Almost ready to try loiter next, once someone more experienced than myself has had a look at the logs and decided there is nothing else that needs fixing...!

            Thanks so much folks.

        • Ahha! Perhaps its my barometer then. I mentioned my concerns for prop wash at the start - It is not protected from sunlight at the moment - but i have an enclosure it will be going into ASAP.

          I read up here: http://diydrones.com/profiles/blogs/important-note-for-apm-2-5-user...

          He describes when the barometer is not shielded, when he switched it over to altitude hold mode it shot up into the sky - thats exactly what mine did!

          So i will put it in an enclosure and try altitude hold again. As loiter uses altitude hold  this could be the problem with loiter aswell?

          Also, you mentioned that the GPS altitude was nice and steady so any ideas what all those GPS errors are?

          Thanks, so much - i will post back ASAP with the next flight.

          • do you have a legit apm? I've got the rctimer version, and their setup guide explicitly tells you to glue a piece of black foam over the barometer (haha)

            very last picture in the first post: http://www.rcgroups.com/forums/showthread.php?t=1897295#post25070306 

            RC Groups
            RC Groups - the most active Radio Control model community: electric and fuel rc airplanes,rc helis,rc boats and rc cars. Features discussion forums,…
  • You need to make the throttle is between 40-60%, or throttle is at middle to get altitude hold and loiter

  • Watch Randy's excellent Arducopter 3.0 Pre-arm, maiden flight and compasmot vidoes and do everything in them to get started.




    The HDOP value is available in mission planner if you have the telemetry radio connected.

    • Thanks, i will check through those steps, and get a log from the IMU and post back with it asap.

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