Heavy-Lift machines with 29" - flying issues

I'm struggling to find a decent PID Setting for a 29" coax octo based on the Pixhawk with the latest firmware.

The problem is, that I am able to get a fine setup for no wind conditions, then the machine flies really well. But as soon as some light wind gusts occur, the copter is shaking and struggling and I have to fight on the sticks to keep it calm.

Hardware:

Pixhawk with latest firmware,

U8 with 29" props coax octo,

Herkules escape board with custom firmware tested with U8 engines,

AUW with simulated payload is 19kg.

At the moment P is 0,18, I is 0,11, D is 0,020.

One possible problem could be some vibration issues on X (green) and Y (red). I can clearly see that the flight performance gets worse during the flight, and by looking into the logs you can see that vibrations get heavier til the point where the copter starts to get uncomfortable to fly.

Apart from trying to mount the Pixhawk on some vibration absorbing gel pads and using some thinner cables to minimize vibration transfer, does anybody have some suggestions for me?

accxylog.PNG

20150214_200218.jpg

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Replies

  • Fix vibrations first, but unless it's very heavy, the disc effect will let wind play with it.
  • T3

    @Zwonimir,

    I have similar issues with one of my hexas. But, my vibrations are a magnitude lower. Although our copter is a magnitude heavier. Maybe both are a little underpowered for the total AUW. Is there a difference without payload?

    From your photos I cannot see the vibration damping of the pixhawk. But it definitely looks like vibration transfer. 

    The only other suggestions without knowing more details about your setup is balancing the props and motors (in combination). 

  • A good way to get rid of vibs is make a new plate on the top of the copter and put the Batteries and the PixHawk

    all on the one plate and rubber mount the plate with these...  That will help a lot..

    http://www.mcmaster.com/#vibration-damping-sandwich-mounts/=vwrhum

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