P4 Oscillations In Flight - Cannot Find Cause

[Hands0n]

I did check a couple of hover segments from the flight record that @Hands0n posted - those had no obvious oscillatory behavior comparable to what was visible during forward flight. I can post the details later if anyone is interested.

In regular flight, at moderate stick movements, so moderate horizontal speeds, the P4 flew without any obvious oscillation. I tend to fly "briskly" unless taking specific video photography. And a lot of that flight was being performed by a friend who is learning to fly, and so was slow to moderate speeds. When I took the controls and gave it a bit of a thrashing at speed in goth GPS and Sport modes it became apparent.

At full forward Pitch the oscillation would be immediately apparent. It was a calm still day and there was a slight wobble at hover, unusual for a Phantom and witnessed by almost all of the similarly affected on the forums.

I tried Left and Right Roll and there was no visible evidence of the oscillation. I'm not sure about Pitch backwards, don't recall.

On fast vertical descents the oscillation was very pronounced, even more than purely horizontal. It was a bad whether descending vertically in its own column of prop wash or while travelling forward (ie. 45 degree descent rate). All of those moves should be in the logfile that you have - as by then I'd fully realised something was wrong and was poking at it from all angles, so to speak

 

[Hands0n]

It might also be interesting if @Hands0n could perform an experiment with inputs full right aileron, then full left aileron, and then full back elevator. Would there be the same oscillatory behavior, and would it be along the same axes.

Hey, I'd love to do that but have already rolled back to 01.02.0602. If I ran through the update again there's no guarantee that it will break - it may actually work this time However, I do plan on re-trying the update but was going to follow the guidance of DJI (above) to see if it works to give me a reliable 02.00.0106.

The thing is, I'm not able to get to the flying field until Saturday, so if you'd like me to try the above it will have to wait until at least then.

 

[Hands0n]

Latest update:

I went out in the back garden with 01.02.0602 but the DJI Go 4 app notified me of restrictions to height and distance and warned of inconsistent software! However, I did fly it around a bit to see what it was like and it felt like my good old P4 was back with me again. Now, did I want to work my way around what was not happening or should I just go for 02.00.0106?

I decided on the latter, and just worked through the "procedure" to update as advised by DJI (see a few posts back earlier).

After the update to 02.00.0106 I went back out in the garden, its slight breezy always there, I've nicknamed it The Wind Tunnel .... and then took an initial flight with the SD card not installed (as advised). The P4 flew perfectly, no problem whatsoever other than handling the breeze as I'd expect it to and as previous versions. So I popped the SD card in and repeated the flyabout in the garden. Perfect. No trace of its previous hypersensitivity. Although this isn't exactly the same as in the field, I did manage a few bursts of full stick both Pitch forward/reverse and Roll left/right. Hopefully you'll see these in the log file if you fancy another look.

I have left a 97MB .zip of all the short garden flights since the successful update on Google Drive if you'd like to look at the new firmware after what looks to be a successful upgrade of the firmware.

Hands0n-02.00.0106.zip

I'd be very interested in what you're seeing now. The longest flight with the most stick banging is FLY150.DAT

 

[Mavericksan]

Hi guys, thank you for the detailed study. The video segment is part of the FLY127.DAT flight. I got my colleague to perform a fly by with full forward pitch. It also behaves really crappy when descending vertically into its own propwash, so I'd expect a little oscillation but not as much as is apparent, it almost looks as if its about to flip over.

But vertical descents aside, it is the horizontal flight at large forward pitch that manifests this strange oscillation. My feeling is that it has arrived with .1000 firmware update, but I cannot be 100% certain of that. I updated last weekend, the P4 complained at the field of IMU No.1 issues and switched to No.2. I recalibrated the IMU in the field, and back at home, but do not recall this issue on that day. It feels like it only started today, and was consistent across three battery swaps.

The aircraft is stable vertically, I'd also say that there is no particular evidence (in flight) of the Roll being affected like this. I'm going by eyesight of course, so could be wrong, the charts above suggest that I am [wrong]. It is literally only the Pitch (I'd say forward as well as back). That disparity that @sar104 has observed above is what I see in flight, and in that video clip.

Would it be worth running the IMU Recalibration again or do you fellas think that I have a physical fault with the P4 (I hope not, its only just out of warranty!!!).

Or could it be the TX itself and not the P4 at all??

This is absolutely the same behavior, I am experiencing with my P4. [emoji35]

I posted here some minutes ago before I noticed this discussion....

 

[Hands0n]

****! I spoke too soon. I skipped off work a bit early, went down to the field to try this out properly and .... no change.

This issue only affects forward flight. It does not affect Reverse or Left/Right Roll. In the included video segment you can see the forward and back, I didn't record left/right roll. But those were as smooth as ever.

I also experienced one solo incident of the Camera Gimbal locking up to the bottom left. Not seen that previously and a restart of the P4 saw it not happen again across three full 20 minute duration flights. I don't think the battery use is higher.

So, the next step will be to try that other suggestion which was to recalibrate the VPS and see if that makes any difference.

 

[Mavericksan]

****! I spoke too soon. I skipped off work a bit early, went down to the field to try this out properly and .... no change.

This issue only affects forward flight. It does not affect Reverse or Left/Right Roll. In the included video segment you can see the forward and back, I didn't record left/right roll. But those were as smooth as ever.

I also experienced one solo incident of the Camera Gimbal locking up to the bottom left. Not seen that previously and a restart of the P4 saw it not happen again across three full 20 minute duration flights. I don't think the battery use is higher.

So, the next step will be to try that other suggestion which was to recalibrate the VPS and see if that makes any difference.

That's exactly the same behavior I see at my P4. And it flew so smooth in the past. Is DJI aware of this?

 

[David Cooke]

I'm interested in that too . . .Thanks everyone for the really excellent feedback . . . and I'm out the door right now to do a full functional test on the flightware 01.04.0602 . . (which it says is "current") before I downgrade to v01.02.0602 as above . . see how that behaves . . . then if no change maybe back to 01.04.602 and see if anything is fixed. Will post later today.

Well here's the feedback . . in v01.04.0602 it's jumpy and unsteady particularly in TRIPOD . .got some video but nothing very obvious with an iphone while flying! . . .but I seem to have screwed up the downgrade somehow and have a very unresponsive P4P now . . .will see if I can get it back and then report more for you . . .otherwise maybe a boat anchor report . . . but only if I can find a piece of rope.

 

[sar104]

****! I spoke too soon. I skipped off work a bit early, went down to the field to try this out properly and .... no change.

This issue only affects forward flight. It does not affect Reverse or Left/Right Roll. In the included video segment you can see the forward and back, I didn't record left/right roll. But those were as smooth as ever.

I also experienced one solo incident of the Camera Gimbal locking up to the bottom left. Not seen that previously and a restart of the P4 saw it not happen again across three full 20 minute duration flights. I don't think the battery use is higher.

So, the next step will be to try that other suggestion which was to recalibrate the VPS and see if that makes any difference.

Do we have a DAT file showing the different behavior forwards vs. sideways and backwards?

 

[Hands0n]

Do we have a DAT file showing the different behavior forwards vs. sideways and backwards?

Somewhere in the pile of DAT files I accumulated today, yes. It was on the last battery that I did the flight video above so if I zip up the last one or two DAT files it should show you the data. I'll grab the files tomorrow evening and put them up on here for you. Sorry, can't do any earlier.

 

[Hands0n]

That's exactly the same behavior I see at my P4. And it flew so smooth in the past. Is DJI aware of this?

Yes, DJI have been aware since the firmware was released in July. Their forum is buzzing with this issue yet since July to now September there has been nothing even admitted by DJI by way of acknowledgement. Its complete radio silence from them.

 

[Hands0n]

Well here's the feedback . . in v01.04.0602 it's jumpy and unsteady particularly in TRIPOD . .got some video but nothing very obvious with an iphone while flying! . . .but I seem to have screwed up the downgrade somehow and have a very unresponsive P4P now . . .will see if I can get it back and then report more for you . . .otherwise maybe a boat anchor report . . . but only if I can find a piece of rope.

When applying the downgrade using Dumldore perform the routine twice. I and several others found that the downgrade first time isn't completely successful, a telltale seems to be that it takes longer to power off the aircraft. After a second run through with Dumldore the firmware seems to apply correctly.

You will get warnings that altitude and range are restricted. I fell for that one. Someone said above that there is no actual restriction and can be flown as normal/usual.

 

[David Cooke]

When applying the downgrade using Dumldore perform the routine twice. I and several others found that the downgrade first time isn't completely successful, a telltale seems to be that it takes longer to power off the aircraft. After a second run through with Dumldore the firmware seems to apply correctly.

You will get warnings that altitude and range are restricted. I fell for that one. Someone said above that there is no actual restriction and can be flown as normal/usual.

Thanks for that . . I need something that makes sense . . . nothings much seems too. Will give it another shot. It's pretty unresponsive now.

 

[Hands0n]

Thanks for that . . I need something that makes sense . . . nothings much seems too. Will give it another shot. It's pretty unresponsive now.

The logic to whats going on with these updates is thin on the ground. It baffles me why some will update and others will not, some with a couple of repeats, others not at all. In all my time working with FCs from other manufacturers I've never seen anything like this. Chinese software is a fickle friend.

 

[hunterxero]

After having issues with the vision sensors not being able to calibrate on the DJI Assistant, I performed the following
1. downgrade firmware
2. Reset factory defaults
3. Reboot drone
4. re-apply downgraded firmware
5. reset factory defaults
6. Reboot drone.

I powered on and diagnostics (and vision sensors) came up ok. Flight tests tomorrow.

 

[Hands0n]

After having issues with the vision sensors not being able to calibrate on the DJI Assistant, ...


I powered on and diagnostics (and vision sensors) came up ok. Flight tests tomorrow.

Some who've had problems calibrating the VPS have had to change the resolution of their PC display, or use another monitor entirely.

Good luck with the flight test

 

[Mavericksan]

Some who've had problems calibrating the VPS have had to change the resolution of their PC display, or use another monitor entirely.

Good luck with the flight test

Well I flew it this later afternoon with calibrated VPS and V02.00.0106 fresh loaded.

No changes - it flys like gliding over a bumpy road. The noise of the motors sound like it's braking every 2-3 seconds. Flying backwards, sidewards is definitely better. Flying forward while ascending is much better than flying horizontally. I switched off all those fancy ground detection features - no improvement at all.

For me it looks like the front VPS is kicking in randomly and forces the P4 to brake. I also observed situations where the craft almost did a full brake without any obstacles in the front. The contrast of the ground might have changed in these full brake situations - the P4 almost had an angle of 90 degrees as it might have at full brake.

Airdata show those full brake events and there is not any obstacle. The height was pretty low, okay......

I'm very disappointed about this crazy flight behavior of a such nice flying bird in springtime.

 

[sar104]

Well I flew it this later afternoon with calibrated VPS and V02.00.0106 fresh loaded.

No changes - it flys like gliding over a bumpy road. The noise of the motors sound like it's braking every 2-3 seconds. Flying backwards, sidewards is definitely better. Flying forward while ascending is much better than flying horizontally. I switched off all those fancy ground detection features - no improvement at all.

For me it looks like the front VPS is kicking in randomly and forces the P4 to brake. I also observed situations where the craft almost did a full brake without any obstacles in the front. The contrast of the ground might have changed in these full brake situations - the P4 almost had an angle of 90 degrees as it might have at full brake.

Airdata show those full brake events and there is not any obstacle. The height was pretty low, okay......

I'm very disappointed about this crazy flight behavior of a such nice flying bird in springtime.

It looks pretty clear that your issues really are braking events. However, that is not the case for the flight logs that the OP posted.

 

[hunterxero]

After the downgrade (see post #54 above), I flew a some full forward stick flights and am happy to report smooth flights without oscillation. It's pretty clear to me now, that the bucking flight was caused by the July firmware update.

 

[Mavericksan]

After having issues with the vision sensors not being able to calibrate on the DJI Assistant, I performed the following
1. downgrade firmware
2. Reset factory defaults
3. Reboot drone
4. re-apply downgraded firmware
5. reset factory defaults
6. Reboot drone.

I powered on and diagnostics (and vision sensors) came up ok. Flight tests tomorrow.

Why did you do steps 2 and 5?

 

[hunterxero]

These steps were from recommendations on posts in DJI's forum which has a lengthy thread on the problem.

Previously, I had tried just doing the downgrade once without the Reset factory defaults. The result was stable flight but no vision positioning sensors.

The steps outlined above resulted in a smooth fully functional P4.