Octocopter spins out of control

I’ve replaced a DJI Wookong-M with a PixHawk and all of the options including the 3DR compass and GPS. I’m yet to have any kind of successful flight. As soon as it leaves the ground it starts to spin rapidly in a clockwise direction.

All of the other electronics are exactly the same as with the Wookong-M config including the motors, ESCs, Power Distribution board, etc. I’ve verified that all of the motors are spinning in the right direction, in the right order and that they are level.

The PixHawk is mounted upside down facing forward in the center of the octo and the external GPS/Compass is mounted on one of the arms about 8" from the center of the frame. I’ve set AHRS_ORIENTATION = 8. All calibrations have been performed. The trims on the transmitter (Graupner MX-20 in Mode 2) are all set to zero.

I’ve attached the log file from the last attempt at flight. Any and all feedback welcome.

Here’s the output from an Auto Analysis:

Log File C:/Program Files (x86)/Mission Planner/logs/OCTOROTOR/1/2015-06-07 13-53-47.log
Size (kb) 1251.255859375
No of lines 17215
Duration 0:01:55
Vehicletype ArduCopter
Firmware Version V3.2.1
Firmware Hash 36b405fb
Hardware Type
Free Mem 0
Skipped Lines 0

Test: Autotune = UNKNOWN - No ATUN log data
Test: Balance/Twist = GOOD -
Test: Brownout = GOOD -
Test: Compass = FAIL - Large change in mag_field (46.96%)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = GOOD -
Test: GPS = GOOD -
Test: IMU Mismatch = GOOD - (Mismatch: 0.24, WARN: 0.75, FAIL: 1.50)
Test: Parameters = GOOD -
Test: PM = WARN - 5 slow loop lines found, max 8.53% on line 4899
Test: Pitch/Roll = GOOD -
Test: Thrust = GOOD -
Test: VCC = GOOD -

What’s the Test: Compass = FAIL - Large change in mag_field (46.96%) about? I thought I had successfully completed the compass calibration.

Have you run the compass_mot?

Plotting mag2 magx, magy and magz against throttle output it shows a lot of variance that follows your throttle output perfectly.

The motor outputs between DJI and Pixhawk are not in the same order. Run the motor test and make sure they power up in the correct order…


Yes, I know the PixHawk motor order is different than the DJI. As I said in my original post, I’ve run the motor test and all motors spin in the proper order.

I looked at the CompassMot calibration instructions and I’m not sure how to do it with my octocopter. The bloody thing is nearly 5’ in diameter and weighs almost 20 lbs with the batteries. Any suggestions?

Just follow the instructions here - copter.ardupilot.com/wiki/ac_com … and_motors

Given the size of the octo, you will probably be better off doing it outside, I do it that way on my quad and it’s always worked well. Have never needed to “tape it down” either.

My power module (ATTO180) is only monitoring voltage. Will this procedure still work?

Without current the compassmot uses throttle position which doesn’t work as well as current monitoring.
Personally, I’d give it a try to see if it helps. Can always reset the compassmot results to 0 if it doesn’t.

Here’s a screenshot of the Mission Planner Compass Motor Calibration screen. I’m guessing an interference number of 6 is pretty good? I’m using an external 3DR compass and GPS so I would have thought the signal interference would be minimal. How important are the cable lengths? I had to use a little longer cable for the I2C to compass interface in order for it to reach.

Thanks for all of the assistance!


I’m fresh out of ideas. I just tried to fly again after doing the Compass Motor test, disconnecting the external compass, calibrating the internal compass and it still just spins out of control.

Any other ideas/suggestions?

Looks like motors 3,4,5,6 are running hot causing the copter to turn Clock wise but it actually is turning Counter Clock wise. Maybe you have the props on backwards or the motors are turning the wrong way.


You synopsis appears to be correct. I actually had both situations. Props on the wrong motors which were spinning the wrong direction. It appears I overlooked the fact that the Pixhawk and DJI Wookong-M want things spinning in opposite directions.

I’m about to give it another flight test…

Flight test successful!!!