Hello.  Just wondering if I could get some advice.

Since day one, my hex has had a problem with uncommanded roll/pitch.  I think (its hard to tell with the control issues) I have gotten my rate pids pretty much dialed in.  When I find the sweet spot (slightly forward and to the left on the stick) it hovers nicely.  The moment I let the stick center the thing rockets off to the right (~10 degrees) and begins a slight drift backwards.  I was able to trim out the aft movement, however, even with maximum left trim, the copter still wants to shoot off to the right.

Things I have done:

  • Balanced the props with a magnetic prop balancer.  I have been using this for a while and have always had good results on my other planes/helis.
  • because my hex has tubular arms, I built a fixture that holds my BeastX digital pitch guage and mounts on the prop shaft.  Each motor is 0 degrees +/- .2 degrees (with respect to the frame)
  • Leveled the frame during the accelerometer calibration to 0 degrees, again using the BeastX pitch guage
  • Before each flight, I level the frame with a spirit level and invoke the "preflight sensor calibration" from mission planner.  Is this the same as running the "level" command from the CLI?  After doing this the AHI is dead level.
  • I have tried several vibration control solutions on the APM board.  I started with one piece of thick vibe isolating gel under the apm and then moved to four individual (about .5"x.5"x.25") pieces at all four corners with a rubber band providing some downward force on the gel pads.  I noticed no difference between these two methods.
  • I tried various trim methods (as mentioned above).  In most cases I can get rid of the aft movement with a small amount of trim however the uncommanded roll to the right happens no matter how much trim I use.  I have gone all the way to 100% left trim.  It makes no difference.
  • Verified "X" configuration, proper motor rotation, prop placement, etc... The obvious stuff. 

The only other thing I can think of is to move the motors around on the frame to see if something changes.  Possibly one motor is putting out more/less power than the others?  I would think that the APM would adjust for this unless its too extreme.  I really don't want to do this as it will require a complete disassembly of my hex.

I will include the log files from my most recent flight as well as an excel file showing telemetry from the Z accelerometer with each motor running individually.  I'm thinking that some sort of vibe issue may be causing this but I'm no engineer and this data only kinda makes sense to me.

Sorry for the long post, just wanted to be through.  Anything else one would need to troubleshoot this problem I can provide.  Thanks for reading and or providing any help!

Andrew

prop vibes.xlsx

2013-02-24 09-44 11.log

2013-02-24 09-01-24.rlog

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Replies

  • Just a question  on your procedure for level.

    Are you using the CLI level or the Level command in the configurations tab?

    Apparently the CLI level does not do good things with 2.9 and the Accelerometer calibration should be used in the Level screen of the Configuration tab.

  • Just an update...  I calibrated the ESCs individually and it helped a little.  I was able to completely remove the backwards drift however the uncommanded roll is still present.  No amount of trim corrects this.  While flying yesterday I did figure out that if I allow it to take off (kinda just let it go where it wants) it eventually corrects itself and levels out almost completely.  Now I'm beginning to think that it's a setting I don't have dialed in properly.  I'm just not sure what one would cause this type of behavior.  When I allow the stick to center, the hex rockets off to the right but then correct after abut 20 or 30 feet.  What should I adjust? Or am I completely wrong on this?

    Thanks.

  • Hey Jeff, thanks for the reply. My motors only go on one way so I doubt this is the issue. I wish it was this simple!
  • Does it always roll/pitch in the same direction regardless of wind or heading? I was having the same issue and realized that one of the motor screws was in the wrong hole about 2 cm off. If this is the issue, you will be able to see a slight asymmetry when you spin the prop on the motor with the issue.  

  • Hey Andrew,

    I used to have very similar issues with my first quad. Here is what I did to address it:

    - I run the manual esc configuration per the wiki as I feel I get better results
    - when attaching the battery to your Copter, be sure that it is completely level, when powering the system, the gyros will spin up and set level, if your copter is out of level it will attempt to set each time you give it throttle
    - be sure that when you are done flying that you disarm the motors before removing the battery so that the system holds its settings
    - after any longer flight times, I always run the level command from the cli, I have had better luck using this
    - if you haven't already done it, find a windless area (gym or big room) and fly in auto trim mode to let the copter learn from your control adjustments
    - after trying all of the above, perform the hand test which will let you feel if there is still any pull to one side or the other without risking damage

    Hope this helps!
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