AC3.3 Vibration Logging Discussion Thread

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Gerhard Laubscher May 19, 2016 at 8:19am

Hi Group,

Feedback -

Following on on my discussions and experience re Vibrations - (I have included the flight-log bin-file, compressed)

As you may have followed my attempts, the ad hoc 'Eraser' effect dampened the FC, which inturn reduced the vibrations, particularly in the Y-axis. Vibe plots very much improved, AFAIK.

I then made the 'Eraser'-effect permanent -

1. Found a piece of Plumbers Lead-bar a the local Plumber.

2. Hacked off a piece, flatten it with a hammer, added Devil-Tape (dble-sided) Weight = 24g

3. Fitted it underneath the MountPlate of the PixHawk FC

4. Plotted Results -

IMU XY

IMU XYZ

Vibe XY

Vibe XYZ

Des Att Roll

Des Att Pitch

Conclusion -

Adding the damper weight, did reduce the XY vibrations within acceptable limits, as I understand the wiki.

It also improves the Des/Att Pitch and Roll, making the craft 'feel' more solid in the air.

Last concern - Vibration on the Z-Axis seems to be 'high', however, is it within acceptable limits?

Your feedback and input?

Regards,

Gerhard

2016-05-19 11-31-43.rar

FC_Lead_Weight.rar
- T3
  
  Thorsten > Gerhard Laubscher May 19, 2016 at 1:19pm
  
  Hi Gerhard,
  
  your vibes look ok now! However, adding weight to the mount is treating the symptoms, not the cause. Moreover, you add weight to your system. I am pretty sure it is the unbalanced props causing the vibes. I had similar symptoms on my first copters. Carefully selecting props and balancing them should solve your problem. I suggest to follow Forrest Frantz's "Secrets of Prop Balance, Tip Trace, and Dynamic Balancing" at:
  
  http://diydrones.com/xn/detail/705844:Comment:1889772
  
  You can test each motor/prop combination and thus the effect of balancing using the motor test function in Mission Planner. Try different speeds and look at the resulting vibrations separately for each prop/motor combination. You can see and feel them. You can also use a cell phone with some vibration meter app as an indicator or use logging before arming to analyze the vibes in more detail.
  
  In many cases cheaper props cannot be balanced. Then try another prop with the same motor.
  
  What might also help additionally is replacing the dampers with softer ones.
  
  Cheers,
  
  Thorsten
  - Rob_Lefebvre > Thorsten May 19, 2016 at 3:48pm
    
    You can balance the props all you want, but they'll vibrate as soon as you start moving through the air anyway. Dissymmetry of lift.
    - T3
      
      Thorsten > Rob_Lefebvre May 19, 2016 at 11:58pm
      
      Sure, but this is a different and additional kind of vibration.
  - Vesselin Goranov > Thorsten May 19, 2016 at 3:24pm
    
    The props making different vibrations, but it is easy to measure those by the smartphone apps like Seismograph.
    
    Y vibrations can be caused by many factors, but seems there the folding legs are the source.
    
    Z vibrations are normal.
    
    Anyway, it is better to have "calm" controller, for safety and well controlled flight.
    
    All large frames do have vibrations. I have experience with 6 different types 800+ frames, and all cannot work well without additional weight in the controllers - simply the Pixhawk is too light for that standard rubber dampers.
    - T3
      
      Thorsten > Vesselin Goranov May 19, 2016 at 11:54pm
      
      Right, the Pixhawk is too light for these dampers on larger copters - especially when under tension. I use softer ones in a normal vertical mount on my 900 frames without any additional weight. But you have to find the right balance between too soft and too hard.
Ivan R May 19, 2016 at 7:12am

i have read this thread and the wiki and i still have no idea how to interpret the clipping stuff on AC3.3 vibes....is there an explanation for the dumber of us somewhere? :)
- Gerhard Laubscher > Ivan R May 19, 2016 at 7:37am
  
  I agree with you Ivan,
  
  call me a novice, but I don't understand how to use the 'Clip0,1,2' either in conjunction with the Vibe xyz
  
  Gerhard
  - Vesselin Goranov > Gerhard Laubscher May 19, 2016 at 7:53am
    
    "Clip" represents the max level, the sensors and EKF can manage - it is like the sound, when the level is too high, the amplifier is overloaded, cannot reproduce and "clips" - i.e. cuts the signal.
    
    Looking at the clip diagram, can see how many times and how long the system was overloaded, was not able to interpret the respective data.
Rob_Lefebvre May 19, 2016 at 5:05am

Wow, thread necromancy!

And what timing. I just got done helping somebody tune another very large copter which was having severe flight control difficulties due to vibration, though the Vibe message showed everything was fine.

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AC3.3 Vibration Logging Discussion Thread

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