Custom frame, very similar in layout/size/design as the DJI S1000
DJI e1200 Pro propulsion (motor/esc/prop combo). These ESCs require manually setting the MOT_PWM_MIN MOT_PWM_MAX PWM range [1050, 2000].
Pixhawk w/ AC 3.4.4
The maiden flight was done in loiter mode, with the intent that this would be more stabilized than AltHold or Stabilize modes. Should maiden flights always be performed in Stabilize mode? By going straight to loiter, did I prevent the system from auto-learning something?
The flight was short (30 sec total?):
Immediately started rapid toilet bowling: maybe 0.5 to 1 revolution a second. The copter spun in this manner all the way through to crash.
Copter kept increasing in altitude, despite me cutting out throttle entirely.
Copter eventually inverted and quickly descended with a hard impact.
Flight path was an arc, almost like a rainbow in shape.
Preflight checks:
Compass cali was done just prior to flight, using onboard cali.
Accel cali was done in the shop
Confirmed correct motor order in shop (using MP motor test)
Confirmed motor rotation and prop directionality just prior to flight
Prior to lift off, I rev’ed up the motors but not enough for lift off; I examined those logs and everything looks normal. (happy to upload this log as well).
Looking at the logs and auto-analysis, it looks like the primary cause was magnetic interference with the compass. Can I get a second set of eyes?
What could I have done to prevented or mitigated the outcome of this flight?
I’ve heard of some people having a kill switch on their radio.
How can I test magnetic interference prior to maiden flight?
Sorry to hear about your crash, but you skipped way too many steps.
No.1 - Keep Stabilise as a fall back mode for all testing.
No. 2 - Start test flights in Stabilise.
No. 3 - Move upwards in automation in your flights slowly. By this I mean, once it flies nicely in Stabilise, select altitude hold, then, once you have it flying nicely go to position hold, and then loiter. If all is good in Loiter then it’s time to test things like RTL.
You will find you need to make adjustments and tuning at each stage as the default values will get you in the air but cannot predict the handling characteristics of each machine.
That’s when you will be doing your auto tune.
Ok, Toilet bowling is where the copter starts to move around in a circle that becomes larger with each turn.
In your case you were in a spiral where the copter was spinning around in a circle. Not good. I would check the motors and motor direction. You may have the motors in the wrong order or spinning in the wrong direction.
Use Mission planner and the motor test screen and check that the motors spin in order.
Stabilize is the best mode to test that the copter will function correctly. Loiter is an assisted mode and will try to fly itself assuming that the hardware is functioning correctly.
Thank you both for the guidance. Sounds like the consensus is: always start in stabilize on a new build.
@iseries, Updated title; you are right, it was spiraling/yawing rapidly, not toilet bowling.
I feel a bit dumb; this isn’t my first AC rodeo (maybe my 5th pixhawk setup now?). I’ve found loiter to be my favorite mode for tweaking thinks/checking telemetry (for errors/etc), so I mistakenly figured I would just start there. I even re-read the first flight docs prior to this flight, but mistook that for people who are doing their first flight with AC, not necessarily their first flight with a new build. My mistake.
I am going to triple check the motor order and motor+prop direction to verify those were all setup correctly.
Would love input on what others think about the compass interference. (I will be looking at alternative mounting positions).
The only time I have see this was on a DJI S900. If your using any after market arms, or motor mounts, be sure to closely monitor the degree of tilt in each motor mount. If your still using stock motors and mounts, be sure to check the vibrational bushings, if the blow out, which they will, then it can effect your bird.
Secondly, you should remove your props and perform an all in one ESC calibration, this will ensure that your ESC are mapped to the exact Pulse Width Modulation (PWM) values that your Remotes controls throttle (RC3) is putting out.
Check your GPS_NAVFILTER parameter also, and make sure that it’s set to the default value.
When performing you magnetometer (Compass) calibration, make sure that your using the strictest setting that your Compass in both the Pixhawk and your external GPS puck can handle. Also, don’t introduce more metal to the bird after performing this calibration.
Lastly, I️ can almost guarantee you that you need to do an all in one ESC calibration, just search Pixhawk all in one calibration on YouTube. If that doesn’t work then pay close attention to motor mount orientation. if this stuff doesn’t work, then hit me up again and I will give you some more stuff the try.