Bouncing hover

Hello, I have an issue with my Phantom 3 Advanced. From one flight to another, it started to ‘bounce’ during hover flight. There is a battery error coming up after a couple of seconds of flight. The cells voltages are completely unbalanced and are varying rapidly on all 4 cells. It was working perfectly the flight before.

Here is what I tried already:

  • Compass calibration
  • IMU calibration
  • Drain the battery drain under 5% and charge it again to 100%
  • Force-update the firmware (with the DEBUG file)

Nothing worked.

Here is a video showing the problem:

I’m not sure if the battery unstability is the cause or the consequence of the problem. I’m looking for someone who could lend me a battery for a quick test, but in the meantime I would appreciate your help.

Hi there, so I bought and installed a new battery, I changed all the 4 propellers, but the problem is still there. I tried to adujst the gain settings as well with different values (I saw that 90 / 90 / 80 / 100 was supposed to work better), but it did not help either.

Can someone help me?

If you can provide the .DAT log file maybe we could determine the cause. Look here
to see how to retrieve the .DAT. It will be large so you will need to use a public sharing site like Dropbox or GoogleDrive.

Hi BudWalker, thanks for you answer. I retrieved the .DAT files, the drone produced two files with roughly the same size and date, so I put them both on the following share:

I hope you can find something in there…
Best regards

I looked at this some but don’t have a clear answer for you. FLY355.DAT shows the problem seen in your video. The motor pulsing can seen clearly in the motor speed data.

and it’s commanded

There is a very odd relationship between the commanded and observed vertical acceleration. Normally, the observed (green) follows the commanded (red) like here

But, in the incident flight the opposite is true at the onset

A defective Z axis accelerometer could cause this but there isn’t data to support this. Has the P3 been dropped or otherwise been subjected to a high impact?

Can you send it to DJI for repair?

Thank you so much for taking the time to analyze this issue, I really appreciate. I think the second graph is not the right one (identical to the first one), but I got your point: the motors are behaving exactly the way the ‘brain’ orders them to, so it is not a motor / propeller / current or voltage loss / frame rigidity issue.

No, my P3 did not crash nor was dropped nor received a shock. This issue appeared out of nowhere, right after the first takeoff after powering it on. I had just charged the battery after the last flight which had no issue at all, everything was perfect and the landing was smooth.
I suspected a Z-axis accelerometer issue too, but you wrote that there is no data supporting this. What data are you thinking of? I guess there is no way to replace a single accelerometer ? Is the complete IMU replaceable ? Is it worth it ?
I don’t think that sending it to DJI for repair would be worth it, I can buy a used P3 Advanced with low hours, two batteries and two sets of spare propellers for around 160 US$, a repair would probably cost more than that.
Do you have some other ideas?
Thanks again for your help.

You’re right about 2nd graph. Try this

While sitting on the ground the Z axis accelerometer was constant at -0.99; theoretically it should be -1.0. That’s the correct value.

The IMU is replaceable. But, I agree, if you can get another for $160 it hardly seems worth replacing the IMU. Especially since it’s unclear, to me at least, if a new IMU would fix the problem.