Trouble getting off the ground

My setup is:
HMF S550 F550 with standard carbon fibre T-Shape Landing Legs
JMT 920KV CW CCW Brushless Motor
30A Brushless ESC Speed Controller
9443 CW CCW Propellers
Pixhawk Flight Controller
6M GPS with Compass L5883 25cm Cable
DJI GPS Folding Antenna Mount Holder Metal
RadioLink AT10 2.4GHz 10CH Remote Control System
No live telemetry yet

In its first build i got it off the ground, but it was crazy light and the wind took it. It landed hard and cracked itself in half.
Post re-build, i haven’t got it off the ground yet.

I took it out this weekend and it just repeatedly wanted to flip itself over, immediately on the ground.
I tried holding it in the air, and same thing, maybe a second of not fighting me then nose dived.
I thought i had calibrated everything as per instructions
motors test out ok, correct order and correct rotation

Im not sure what to look for in the logs - would someone be able to assist?
When i was in the field i had no laptop USB telemetry so it may have been an GPS / Compass issue but auto analyze logs seems to say it was ok.


2017-08-20 16-43-26.log
Size (kb) 2750.859375
No of lines 33060
Duration 0:03:38
Vehicletype ArduCopter
Firmware Version V3.5.0
Firmware Hash 633501f9
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = NA -
Test: Brownout = GOOD -
Test: Compass = GOOD - mag_field interference within limits (18.84%)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = FAIL - ERR found: CRASH
Test: GPS = GOOD -
Test: IMU Mismatch = GOOD - (Mismatch: 0.43, WARN: 0.75, FAIL: 1.50)
Test: Motor Balance = GOOD - Motor channel averages = [1184, 1189, 1167, 1199, 1176, 1198]
Average motor output = 1185
Difference between min and max motor averages = 32
Test: Parameters = GOOD -
Test: PM = NA -
Test: Pitch/Roll = NA -
Test: Thrust = NA -
Test: VCC = GOOD -

next time try flying with position hold. Thanks for sharing your logs.

Firstly there’s not enough throttle to even disturb it in that log.Secondly,it’s usual that props and motor direction are suspect when a new build won’t take off (with a huge chunk of throttle).Sometimes you have to get them in the air before they behave.Lots of checking.

When building or rebuilding :grin: a copter, my first test is to hold it in the air, give it some throttle and test how it responds to roll, pitch and yaw commands from my radio. Still in my arm and in the air, I would then test how it fights to my movement in roll, pitch and yaw axis. If it tries to counterpart my actions all is well. This is all in stabilize mode.

Only then I try to take off from the ground, usually fast for the first meter to take care of the ground effect and then calming it down. Then comes the rest, checking out flight modes, autotune, etc.

Thanks for all the suggestions, back to the field it is…

I’ve been digging through the log and your vibrations are VERY high. X axis peaks at 28.1207, Y peaks at 29.44061, and Z peaks at 60.98232.

There is also some clipping, but that may be due to bouncing on the ground.

I’m wondering how you have the Pixhawk attached to the frame? If you are just using some foam tape, I recommend ditching it and using a damping mount

looking at some photos online i appear to have mounted my pixhawk in the wrong position - high vibration is likely a problem if not the root cause. Im going to strip it down a bit and re-mount with some extra dampening.

Re: holding in the air first - i did this. made little difference.
Did this on the previous build with good results - so i get what youre saying.