Hi Folks, I'm really struggling with an altitude problem on my quad. I've tried every tweak Google and other postings could bring up.  The problems is this:

1) In Alt_Hold or Loiter mode the quad will gradually rise, or more often than not it will sink slowly towards the ground.

2) All the Altitude readings look good, in fact the DAlt readings make it look to me like the quad is simply doing that it thinks it's being asked to do.  But I'm not the one asking. My throttle is mid!  Input levels are the same, but DAlt is graduallys saying "descend".

Nothing I do changes this behavior.  I sometimes randomly get good performance for up to 2-3 minutes, but then it manifests.  Here's a quick log snippet illustrating the issue.  I've also attached a full log for review.  Any help would be tremendously appreciated. I'm 100% at the end of my rope on this.

3691277980?profile=original

Note the DAlt behavior.  Why...in....the....heck....is that changing?  It pulls my quad up, and then takes it down.  My quad is doing what it's told - but told by who???

-Jeff

69-12-31_19-00-00_8.bin

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  • Ok, it looks like your copter is under powered and you need to set the THR_MID value.

    Please refer to this page: http://copter.ardupilot.com/wiki/ac_throttlemid

    It looks like you may need to change something to get it fly correctly otherwise you need to lower the stick when using ALT_HOLD or Loiter mode.

    When you where in loiter mode the stick was at 1671 which is higher than 1500 normally seen when at mid value.  IE your mid stick value should be 1540 (1941-1139)/2+1139.  Since the dead zone is 100 and a value over 1640 is climb it climbs.

  • PROBLEM SOLVED - The issue has nothing to do with my settings and everything to with APM which is behaving extremely erratically for me on my Macbook.  APM is arbitrarily changing settings when I use the sub-menus such as "Basic Tuning" "Extended Tuning", etc.  

    Example, if I dare use the "Extended Tuning" configuration tab, it will zero out the Throttle P value to "0".  Every time.  APM cares not what value is in the board, it will populate that with a "0" in APM and if you dare press "write" it will blow away whatever value was in there before. 

    The same is true for WPNAV values.  I now have to do all tuning directly in the Full Parameter section and I always compare against a known good configuration value before I go flying.  

    I've also noticed that I have to re-start the APM software every time I disconnect from my flight board, and if I dare connect to a PC vs my Mac (I tried that thinking the Mac software was the problem) and it blows away a huge range of settings instantly.

    So tuning my quad is an enormous pain - but it does work, and it flies beautifully.

    • Make sure your Mission Planner is up to date.... I had similar issues in the past, all because I was running an outdated version of the Mission Planner.

  • Ok, the logging needs to be turned up from 893 to NearlyAll so we can see everything that's going on.

    Second it looks like your RC1_Trim is wrong.  Did you do the Radio Calibration?

    • Okay, I turned on the "nearly everything" LOG_BITMASK.  Attached is an updated log that beautifully illustrates the problem.  Note that in this case the quad is climbing steadily in response to the DAlt going up vs. down.  But again the quad seems to be doing exactly what it would think to do.

      I did a Radio Calibration but can do another.  The quad isn't totally stable in yaw or roll, it drifts *ever* so slightly, but it's a really small drift.  I can easily hover in my basement.

      Also note that I can't plot the vibration errors in my log viewer.  It doesn't show anything at all.

      69-12-31_19-00-00_10.bin

      https://storage.ning.com/topology/rest/1.0/file/get/3702619799?profile=original
      • I've tried now with various settings to get the IMU values to graph properly and simply put, they do not.  I can sometimes get AccX to graph, but the others simply show: ERR status when I mouse over the graph to pull values.  Maybe I've got an issue with my Accelerometers?  I just pulled out my last hair.

  • 3D Robotics

    That's almost always due to vibration. Have you vibration damped your autopilot?

    • Funny you should ask, that's on my agenda for tomorrow. The APM is currently on top of a plate with rubber "earplug" feet. So it's fairly isolated from the main quad body. I plan to enable vibration logging tomorrow and review that output. I could put a layer of foam and Velcro between the APM and the isolated plate. I'll post photos tomorrow. Thanks a million for the quick reply!
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