Significant Vibration In GPS Mode Only

[ProPilotWannaBe]

So today I redid several things on my S800:
- Replaced the tall GPS antenna pole with the short one (still 2-3 inches above the props)
- Moved the IMU anti vibe tray to the front
- Replaced one of the props
- Updated the WKM to the latest version
- Updated all of the settings in the Assistant Software as needed for the above changes

But then when I took it flying this evening I noticed a significant vibration I haven't had before. But more oddly, it only occurs in GPS mode. When in Attitude mode it's as smooth as it always has been. I tried lowering the basic gains for pitch and roll, but that did nothing except have it drift more when holding position.

I didn't look at the balance of the new prop, so I'll do that tonight when I get home. But I figured an imbalance would show up in ATT mode as well.

Anybody have any ideas what I should try?

 

[deluge2]

So today I redid several things on my S800:
- Replaced the tall GPS antenna pole with the short one (still 2-3 inches above the props)
- Moved the IMU anti vibe tray to the front
- Replaced one of the props
- Updated the WKM to the latest version
- Updated all of the settings in the Assistant Software as needed for the above changes

But then when I took it flying this evening I noticed a significant vibration I haven't had before. But more oddly, it only occurs in GPS mode. When in Attitude mode it's as smooth as it always has been. I tried lowering the basic gains for pitch and roll, but that did nothing except have it drift more when holding position.

I didn't look at the balance of the new prop, so I'll do that tonight when I get home. But I figured an imbalance would show up in ATT mode as well.

Anybody have any ideas what I should try?

Well that's a lot of changes all at once. I assume the settings updates account for the change in position of the GPS antenna and the IMU. However, presence of vibrations in GPS ATTI mode, but not ATTI mode appears quite telling. As you note, hard to imagine that a single prop imbalance effect would be so mode specific. And it seems unlikely that change in IMU from back to front alone would cause such mode-specific effects. Seems like some GPS antenna change and/or firmware update are most likely candidates. Could there be some instability in Tx-Rx-FC mode settings (seems like there have been occasional reports of mode instability in some setups)?

So you could double check the settings/adjustments for the new physical configuration, confirm gains including advanced, consider undoing GPS antenna change and/or reverting firmware. Maybe it's superstitious, but I would recalibrate everything.

I guess there will be tension between wanting to solve the problem ASAP vs. step-wise approach that might make it easier to get a specific diagnosis.

We'll be interested to see how this plays out.
Steve

 

[ProPilotWannaBe]

Seems like some GPS antenna change and/or firmware update are most likely candidates.

I totally agree with you that those were the two more likely candidates.

So you could double check the settings/adjustments for the new physical configuration, confirm gains including advanced, consider undoing GPS antenna change and/or reverting firmware. Maybe it's superstitious, but I would recalibrate everything.

I did double check settings, and I did recalibrate... I forgot to post those two things I did as well before flying.
So tonight I swapped out the antenna post once I got home, and I'll fly it tomorrow morning and see if that helps.

I guess there will be tension between wanting to solve the problem ASAP vs. step-wise approach that might make it easier to get a specific diagnosis.

Yeah, since I had the whole thing pretty much taken apart since I was moving the IMU, I got a little aggresive and figured do it all. Might not do that again.

I'll post any findings regarding the antenna post tomorrow morning.

 

[ProPilotWannaBe]

Nope, not the GPS antenna. I went back to the original GPS antenna configuration, and didn't eliminate the vibrations in GPS mode.

Any other ideas anybody? If someone can show me how to reinstall 5.22, which is what I had installed prior to yesterday, I can see if that helps.

 

[deluge2]

Nope, not the GPS antenna. I went back to the original GPS antenna configuration, and didn't eliminate the vibrations in GPS mode.

Any other ideas anybody? If someone can show me how to reinstall 5.22, which is what I had installed prior to yesterday, I can see if that helps.

Never done WKM downgrade (or upgrade for that matter), but you need the earlier version of the DJI WKM Assistant SW (v2.00) that I believe will then connect to DJI servers and DL the earlier firmware (v5.22) and upload that into your WKM.

The support/download page is obvious: http://www.dji-innovations.com/download/wookong-m-downloads/

but I didn't realize until now that the "Click Here for Release History" link on that page brings up links to prior versions of SW/FW going back to Jul-2012.

You might want to wait for someone who's done this to chime in, in case there's some key step that's not obvious...

Steve

 

[ProPilotWannaBe]

Ironically i was going to reply to the post and say that I had already tried running v2.00 of the ASW and that it didn't work. Then I thought, well, lemme try once more. This time it did work and I was able to downgrade to v5.22 of the firmware. However, it didn't solve the problem. Still have the not-so-nice vibration in GPS mode. It's not horrible, just noticeable, and enough to make me question things.

Any other ideas anybody?

 

[snurre]

Any other ideas anybody?

I once experienced very unruly GPS loiter after having installed FPV cam and TX onboard. Turned out that some of the cannel frequencies in the 1.2GHz band interfered with the GPS receiver. Have you made any change in your video TX setup?

 

[spartan2381]

Have you tried to recalibrating your compass? I would also check COG, this affected my GPS mode greatly until I entered to correct values. Since you moved the WKM out to the vibe tray have you noticed if sunlight was hitting it? I know there are some issues with sunlight affecting the barometer sensor. I put electrical tape around mine to prevent sunlight from entering. Have you tried resting all values and re-entering them?

 

[ProPilotWannaBe]

I once experienced very unruly GPS loiter after having installed FPV cam and TX onboard. Turned out that some of the cannel frequencies in the 1.2GHz band interfered with the GPS receiver. Have you made any change in your video TX setup?

No, no other changes other than the above. But that is an interesting point for me to keep in mind in the future if I add new video transmitters.

Have you tried to recalibrating your compass? I would also check COG, this affected my GPS mode greatly until I entered to correct values. Since you moved the WKM out to the vibe tray have you noticed if sunlight was hitting it? I know there are some issues with sunlight affecting the barometer sensor. I put electrical tape around mine to prevent sunlight from entering. Have you tried resting all values and re-entering them?

Yes, I did recalibrate the compass, and I have also checked the COG. Both very good points. I might redo the calibrations again tomorrow. While I am at it, I will plan on reentering values. I did verify them with the Bluetooth LED and the registered fine. But again, I'm up for simple stuff like this that might help.
As for the sun hitting the IMU, I am quite sure that isn't the issue. The only reason why I say that is because I first noticed this issue the evening before last when I was flying in total shade (tall surrounding trees late in the day), and again yesterday in my backyard which is totally shaded. Besides, ATT mode also uses the barometric sensor from what I read in the documentation. But again, thanks for any and all ideas. I'm totally game for checking and changing stuff to solve this dilemna.

 

[fd4]

So did you ever find a solution to this? I'm having same problem with s800 and wkm. Very strong vibrations in GPS-mode. I can't use GPS-mode at all because it looks like the whole thing is about to explode in parts... Flying in ATTI-mode is smooth as silk.

 

[ProPilotWannaBe]

No, sadly I never did get to the root of it. I ended up upgrading all my arms to the newer stiffer arms. I also worked on rebalancing everything a bit more. It's acceptable for me now, though if I could ever suggest to DJI that they look at their control laws to improve that, I would.

 

[gtranquilla]

Sun hitting the FC or IMU was only an issue with NAZA from what I recall.
FWIW - I have been using fw 5.20 for a long time without issues but have been reluctant to move up to the newer firmware.
Make sure your IMU is not being bumped from the side by hardware or wires etc.
If your so called vibration is more like a bucking bronco effect it is an issue that can occur when switching back and forth between remote gains control and gimbal control....

 

[soler]

Can you provide some more information on the frequency of the vibrations, Are these slow, 1-2 per second or high I the 20-30 per second area?


Sent from my iPhone using Tapatalk

 

[ProPilotWannaBe]

Can you provide some more information on the frequency of the vibrations, Are these slow, 1-2 per second or high I the 20-30 per second area?

When I was dealing with this issue it was rougly (I'm guessing) a 10Hz range of vibration.

 

[fd4]

Got it fixed! My IMU was attached to IMU mounting plate with velcro for easy removal. Velcro allowed IMU to vibrate a little. I made a more permanent attachment for IMU to IMU plate and now GPS mode is as smooth as ATTI mode. :nevreness:

 

[ProPilotWannaBe]

Got it fixed! My IMU was attached to IMU mounting plate with velcro for easy removal. Velcro allowed IMU to vibrate a little. I made a more permanent attachment for IMU to IMU plate and now GPS mode is as smooth as ATTI mode. :nevreness:

Glad for you. That wasn't my problem since mine was attached to the plate with the recommended tape for permanent attachment.