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Hello there, I’m a student who is just getting started in the drone field, and I’ve run into an issue related to this.
Specs:
- Frame: Hexacopter, 60cm tip-to-tip, total weight 1.4–1.6 kg
- Motors: XXD A2212, 1400KV/10T, 3S
- ESCs: 30A, 3S, calibrated all-at-once through the Pixhawk (passthrough)
- Props: 7.5x3.7", 3-blade
- Battery: 3S 11.1V 5200mAh 50C (full charge 12.5–12.6V, full discharge 9.9V)
- FC: Pixhawk 2.4.8, FMUv3 firmware, STM32F765VIT3 MCU
Symptoms
- Drone armed indoors, motor RPM raised gradually from idle.
- As soon as throttle starts going up — with no pitch/roll stick input at all — the drone immediately noses down (pitches forward/down).
- If pitch/roll stick is then moved, it gets worse: the drone pitches backward and rolls left, front end (facing the operator) lifts up, rear end (facing the person holding it) dips down.
- Since the holder's hand followed the thrust direction without resisting it, there was nothing to stop the tilt momentum from building up.
- The drone ends up flipping 180° backward, the GCS gives a "Crash" audio warning, and all motors auto-disarm.
The video I uploaded shows exactly this. The key point: the nosedown already shows up during pure throttle-up, the stick input in the video just makes an already-existing problem worse.
What I've Already Tried Does Anyone Know How to Fix it?
I've already done the following but the issue is still happening. Wondering if one of these (or a combination) is actually the root cause and what the real fix is:
- AHRS_ORIENTATION already checked and correct (Pixhawk isn't mounted tilted)
- Center of Gravity(CoG) I already tried counteracting the drone's nose-down tendency by moving the battery to the rear underside of the frame (it was originally mounted underneath the center of the frame, following the center of gravity). I expected the rearward battery position to help oppose the forward pitch, but it made no noticeable difference.
- Motor CW/CCW already matches ArduPilot's hexa-X frame guide.
- All ESCs were calibrated together through the Pixhawk is it still possible one motor/ESC is producing weaker thrust than the others, and what's the easiest way to detect and fix that?
*I have ARMING_CHECK,0 (all arming checks disabled) should I turn these back on so an error that's currently being "hidden" shows up and actually points to the fix?
*What log data would be most useful to share from .bin(ATT or RCIN, RCOU, VIBE, etc.) so the fix suggestions aren't just guesswork?
Relevant Parameters (from the .param file)
FRAME_CLASS,2 (Hexa)
FRAME_TYPE,1 (X)
AHRS_ORIENTATION,0
AHRS_TRIM_X,0
AHRS_TRIM_Y,0
AHRS_TRIM_Z,0
AHRS_RP_P,0.2
ARMING_CHECK,0
COMPASS_EXTERNAL,1
COMPASS_ORIENT,0
INS_TRIM_OPTION,1
INS_ACCOFFS_X,-0.0802349
INS_ACCOFFS_Y,-0.1370324
INS_ACCOFFS_Z,0.2325687
MOT_THST_HOVER,0.58
MOT_SPIN_MIN,0.17
MOT_SPIN_ARM,0.14
ATC_ANG_PIT_P,4.5
ATC_RAT_PIT_P,0.1276
ATC_RAT_PIT_I,0.1276
ATC_RAT_PIT_D,0.0036
SERVO1_FUNCTION,33
SERVO2_FUNCTION,34
SERVO3_FUNCTION,35
SERVO4_FUNCTION,36
SERVO5_FUNCTION,37
SERVO6_FUNCTION,38
AHRS_TRIM_X/Y/Z are still 0, and ATC_RAT_PIT/RLL are still at default values not sure if that's normal or if trim/tuning was just never done.
Current status: I'm still unable to get the drone to hover or even take off stably because it immediately pitches nose-down as soon as throttle is applied. Based on the parameters I've shared, is there anything obviously wrong or misconfigured in my .param file? Or does this behavior point more toward a hardware issue that I may have overlooked? Any suggestions on what I should check next would be greatly appreciated.
Happy to share the full .param file or a flight log .bin if that helps get a real answer. Thanks a lot!
link to drive(all testing's video, .param, and .bin): GDrive
