Help analysing logs for new flyer - dropping from sky!

Log Analysis -- deprecated Copter Logs -- deprecated
1

Hi all, looking forward to a long and prosperous membership here.

Would really really love some help troubleshooting my first quadcopter dropping from the sky when I change flight modes, I have read all the wiki’s and looked at my datalogs and solutions aren’t jumping out at me because it is still overwhelming and I don’t know how to decipher the spikes. One thing is that Roll is spiking up and down between 200 and -200 like crazy on the first crash, vs DesRoll, but is this normal to see from a quad falling from the sky?

PX4 (clone unfortunately)

Rundown of first flight and problems:
Take off stable, vibrations look good, voltage looks good, wind was 5m/s (20km/h) so i was pitching against it during take off hence pitch activity in logs
When I got to about 8 metres I put it into Loiter and this was holding position successfully (I was so happy!) until I hit Land mode and it instantly plummeted from the sky.

Quad was fine so I checked everything and went for another flight.
This time when I got to 8ish metres I hit Loiter again and it fell from the sky again. I’m not sure why the first Loiter worked so nicely and then the second attempt didn’t, when I had from 13-20 satellites on GPS and Hdop was good.

Summary:
Flight 1
Take off
[color=#40FF00]Loiter - successful[/color]
[color=#FF0000]Land - drop from sky[/color]

Flight 2
Take off
[color=#FF0000]Loiter - drop from sky[/color]

Alt reading from my baro on PX4 seems to drift upwards but had stabilised (ish) during my flights…

Please let me know if I can provide more information… thanks so much in advance.

2

[attachment=0]throttle anomaly.jpg[/attachment]

Here is some strange behaviour from the throttle??

Motors are AX 2810q 750kv with 30a Afro SimonK ESC’s on PX4
14 5.5 props, a bit big perhaps, I have ordered some smaller ones!

3

I can’t figure out how to edit this into my previous post! Here is another image from my log which seems weird to me.

Desired Alt is plunging well below 0 on both occasions that I’ve crashed. Can’t fathom ever “desiring” such a quick descent. :wink: What would be causing this??

4

Have you tried setting mid throttle?

copter.ardupilot.com/wiki/ac_throttlemid/

5

Thanks for the tip wr420, really appreciate the reply!

I hadn’t set it, but looking at my throttle out it looks like I’m hovering at about 40 to 45% (occasionally dipping below 400, out of the ‘deadzone’), so I have set Throttle Mid Position to 425… Do you think this could be the reason it has fallen from the sky? Is the problem that this has been misinforming the autopilot as to how much throttle is needed to maintain or change its altitude?

According to the logs, on the second crash throttle was hovering at 44% when I flipped onto Loiter and it instantly went into freefall while throttling bizarrely. Is this actually within the 40% to 60% zone that is okay? I’m not sure…!

I am learning a lot as I go and appreciate any info. Despite crashing it has been very satisfying seeing my quad fly, even if only for a couple of minutes. :wink: