Hi all,
I thought I had built the safest drone possible, but it crashed. I’m so sad.
It’s a hexacopter equipped mainly with a Cube Orange flight controller, U8II KV100 motors, Here3 GPS, an H16 Pro remote controller, and a 12S smart battery.
I flew the drone for a while without any problems. However, when returning for landing and about 10m from the ground, the drone started acting strangely, performing two rolls in the sky before crashing.
I really need help to understand exactly what happened. Thanks in advance.
this is the .bin file
Not yet anything close to good analysis, but some potentially useful notes.
This cannot be seen in the logs, the log is cut off less than a second after the “Vibration compenstation OFF”. Might be a poweroff or brownout on the flight controller side.
Throughout the flight, vibration level (VIBE log entries) is very high especially in the Z axis, 20-30 common for IMU1 and 2, reaches as much as 50-100 for IMU3. These are in m/s^2, so the actual kicks might be around 10g! Generally, values below 5 indicate good build quality, values below 10 are considered reasonably safe, around 15 indicates potential control problems possible to creep in, 20 is kind of flyable but shouts out for modifications, 30 is “fix, don’t fly”.
This suggests mechanical deficiencies (including, but not limited to, loose wires near the flight controller), poor tuning (PIDs at near defaults, pitch and roll desired/actual values quite divergent, not a good flying experience) or both.
I would hypothesize the following:
- poor build and tuning overall
- spontaneous switching between IMUs due to high vibrations to trigger rough behavior that did not yet lead into the crash but caused hard target switches which increased vibrations even higher
- some wire come loose (as a result of high vibrations) and cut the power off the flight controller.
P.S.: consider configuring (and maybe calibrating) the current sensor, or someday you’ll miss it.
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your vibrations are really high for starters. looks like your craft is untuned, with how bad the output oscilliations. I am not a pro.
How big is your craft and how much does it weigh?
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High vibrations, all defaults on almost every tuning value other than the notch filter, which is probably set a bit on the high side, no ESC telemetry, and the list probably goes on, but I dug no farther. Clearly no method followed regarding tuning or configuration. This is the inevitable result, unfortunately.
Your battery looks weakly charged, but even that’s a bit hard to discern, since the voltage monitors are basically at defaults. Board power looks reasonable throughout with a slight dip toward the end, but I can’t rule out a power/battery issue as a contributor (including wiring simply vibrating apart).
At a minimum, follow the steps outlined here:
https://ardupilot.org/copter/docs/flying-arducopter.html
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Thanks a lot for your reply ,
Regarding the frame , it’s about 1.4m in diameter, with 6 x 29-inch propellers .
For tuning , I followed the tuning instructions in the ArduPilot documentation, except autotune because I was really satisfied with its behaviour.
I’ve flown this drone many times without any problems , even in strong wind.
I’ll attach the BIN file of the previous flight .
What I noticed as strange behaviour during this flight is:
- When I took off initially, the drone made an unusual movement (visible at the left black arrow, I expect) but then stabilized. I landed it immediately and performed necessary checks.
- I took off a second time, and it performed normally as usual. I hovered for a while, then started moving. When returning to land, the drone again made the same unexpected movement (right arrow) but stabilized once more. I stopped the drone immediately and initiated landing, but the crash occurred as I described earlier
With such big rig you need to be sure you filtering correctly, your notch filtering is wrong, it’s set to 2nd harmonic, but it must be 2 times lower, also your vibrations is high.
IMO you really need RPM filtering and try to lower your vibrations level.
Also clear resonance is seen on ~34 hz.
@Yuri_Rage said it BEST in a different thread…
"Please seek professional, possibly paid help to tune this Copter. Issues this severe + stabbing in the dark to solve them could kill someone.
@amilcarlucas provides services like this and/or can point you in the right direction.’
Even though it looked like it flew well for a few flights there is a lot in the background that you aren’t seeing.
At a min tune your copter with Methodic Config before flying again.
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Thanks a lot for your reply. I’ll take your remarks and advice into consideration.
Yes, it’s clear that I have a lot of vibration and my plane needs more tuning. However, the reason for the crash might be something else. The log recording stopped at about 20m above the ground, even though the battery voltage was sufficient and the vibration was only around 10. Therefore, an electrical failure might be the cause, especially since the flight controller shows no physical damage, but isn’t working. When I connect the FC to my PC via USB, the computer doesn’t detect it.
my guess would be excessive vibrations based on the vibration warning and this from the accelerometers
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This is the cube orange processor board shows no physical damage. But you cannot connect it to computer via USB any more. Attached picture below of the cube orange in question, it may be a hardware failure that caused the crash of the drone.
I don’t know and I don’t think it’s a good idea to just plug in the lone STM32H753. In fact, it has never turned on without the base board connected when I have tried.
It may have been a hardware failure, have you tried different usb cords? Recently I had one go bad on me and thought it was the flight controller.
This is too much speculation and a weird level of forensics. You had a terribly performing craft that crashed. The smoking gun appears to have been high vibration levels coupled with poor tuning that COULD have resulted in some measure of airborne power failure. But we will likely never be able to pinpoint the exact cause of the log stoppage and differentiate it from post-crash damage.
If the autopilot is in such a poor state, it should be replaced regardless of whether you can breathe some life back into it.
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Building a big hexacopter drone isn’t so easy. I’ll rebuild another one and try to make it well-tuned with good performance. I learned a lot from all of you Thanks.
Sorry to hear that. hope everyone is okay What happened?
Thanks a lot. Hopefully, no one was injured.