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Old Yesterday, 03:47 PM
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Joined Mar 2010
70 Posts
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3D printed Quadcopter crash. What went wrong?

Hi everyone,

this is the first flight where I took this quad higher than a few feet, so far I was only hovering in the garden a couple of feet off the ground and stability looked ok.

In this video I was taking it a little bit higher up in the field by my house, then as soon as I decreased the throttle a little bit to initiate the descent, it went into oscillations of increasing amplitude. When it went really wild I did not even try to fix it as I thought it's fxxxxd anyway what's the point. So no, it was not me causing the oscillations, the sticks were neutral.



DaVinci XYZ 3D Printed Quadcopter CRASH with onboard GoPro Black (0 min 22 sec)


Total weight as shown in the video is 1.1 kg (about 2.4 lbs) - 470mm (18.5in) between motor centres. GoPro in sitting on top of the body so not really encouraging CG stability.

Controller is HobbyKing KK2.1 HC - these are the PI settings I was using:

Pitch/Roll: P Gain 25, Limit 60. I Gain 20, Limit 50
Yaw: P gain 35, Limit 60. I gain 25, Limit 50.

Motors are NTM Prop Drive Series 28-26 252W 1100kV with 9x4.7 props
ESC Turnigy Plush 30A

I designed and 3D printed the frame myself - about 210 grams in total.

Interestingly enough, nothing is broken or damaged. It still flies ok!

Thanks
Emiliano
Huddersfield (UK)
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Old Yesterday, 08:09 PM
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Joined May 2012
78 Posts
When you descend too quickly, the props lose lift as they descend through their own prop wash. This causes instability like I think I see in your video as you descend. Your gains may be a bit too high, too, which would make it worse.
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Old Today, 06:31 AM
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Joined Mar 2010
70 Posts
Quote:
Originally Posted by rocketsled666 View Post
When you descend too quickly, the props lose lift as they descend through their own prop wash. This causes instability like I think I see in your video as you descend. Your gains may be a bit too high, too, which would make it worse.
Yeah I've read something similar on a book of helicopter theory but I didn't think it was so easy to enter that condition!

How do I avoid that? Do I always have to make it descend either in a spiral or with a bit of slope, but never vertically?
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