First Flight Oscillation


Went to fly my x4 last week for the first time. This is a large 1600mm (very lightweight) quad using a Pixhawk, running KDE 135 motors and Tmotor Alpha ESCs.

Performed two quick tethered flights. Both times the drone took off and hovered fine, but making a slight pitch caused the drone to oscillate and twitch tremendously and luckily was stable enough to land on all 4 legs.

Pulled the flight logs and performed an auto-analysis, this is the report:

Vehicletype ArduCopter
Firmware Version V3.6.9
Firmware Hash 632be63f
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = UNKNOWN - No ATUN log data
Test: Brownout = GOOD -
Test: Compass = FAIL - WARN: Large compass offset params (X:-122.06, Y:94.98, Z:-368.26)
WARN: Large compass offset in MAG data (X:-122.00, Y:94.00, Z:-368.00)
Large change in mag_field (109.85%)
Max mag field length (690.38) > recommended (550.00)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = GOOD -
Test: GPS = GOOD -
Test: IMU Mismatch = GOOD - (Mismatch: 0.46, WARN: 0.75, FAIL: 1.50)
Test: Motor Balance = GOOD - Motor channel averages = [1351, 1310, 1333, 1314]
Average motor output = 1327
Difference between min and max motor averages = 41
Test: NaNs = FAIL - Found NaN in CTUN.DSAlt

Test: OpticalFlow = FAIL - FAIL: no optical flow data

Test: Parameters = FAIL - ‘THR_MIN’ not found
Test: PM = GOOD -
Test: Pitch/Roll = GOOD -
Test: Thrust = GOOD -
Test: VCC = UNKNOWN - No CURR log data

I am very new to analyzing logs but the compass test = fail which is disconcerting and am wondering if these oscillations are from the large offset in compass or just that the PID tune is just terrible. What is the easiest way to tell or how can you really tell from the logs?

Here is the flight log: Initial Flight Log

Here is the parameter file: Initial Param File

Auto Analysis is of little value. I think you are lucky it didn’t crash flying that large quad on default parameters. Go here:

Hey @memart
Are those t-motor alpha ESCs configured for that particular motor? Those ESCs are FOC.

I was able to get it flying pretty well today! Flew for almost an hour! Decreased the P values for pitch and roll and it got much more stable. Then changed I and D till it was stable enough and everything looked good. So it seemed like the auto analysis failure message had nothing to do with it. Will look into changing those thank you for your input Dave.

Yeah they are fully compatible as I have not had any issues! They seem like solid ESCs to me!

The No ATUN data just means you haven’t run an Auto Tune. I would ignore all the msgs in the Auto Analysis. Once you have the craft basically tuned and flying, sound slikie it is, you can run an Auto Tune which should improve things.

Sure, those ESC’s are fine. FOC isn’t specific for a motor “configuration”.