HUD not matching actual vehicle attitude

[hogster]

Hi all

I'm still tuning my large X8 platform and keep encountering a rather alarming situation where the HUD on the GCS doesn't match the vehicle's attitude when hovering!

So the HUD might be showing a forward pitch / pitch down position, so the system thinks 'I need to give a pitch back command to cancel this forward drift' ... and in the mean time I'm having to fight it by holding forward stick just to keep it level! When I land the HUD then settles itself.

It's quite noticeable when it first 'forgets' what is level as it will suddenly start drifting off quite quickly in one direction.

What's going on here? Is the attitude estimation getting upset by too much vibration? When the platform is on level ground (and actually at any time when it's not flying) the HUD correctly reports the attitude of the vehicle.

Many thanks for any suggestions

David

[LordPikaChu]

Hello David!

Are you using DIMU? Of you're not, your issues are probably caused by MAG interference. When you spin up your motors the interference gets worse to the point when FC cannot reliably resolve the correct attitude. I was having this issues with AIMU as well. Now the drift is completely gone after upgrading to DIMU because with DIMU Autoquad no longer uses MAG to estimate attitude.

The can, of course, also be caused by vibrations, but you would have to post some logs from your flights for everyone to see what's going on there.

[hogster]

Hi LordPikaChu,

Many thanks for your reply

I am using the DIMU, but what you describe does sound very plausible behaviour for the AIMU. I have been able to do things like the TARE and onboard magnetometer calibration so I assume the DIMU is connected and functioning correctly?

I've attached a log file showing a few flights where this mismatch between reported and actual attitude was present.

Many thanks for your help

David

[hogster]

Is it worth trying different firmware to see if this problem still exists? My testing has pretty much stopped dead in its tracks because of this problem as I've run out of ideas of what to try

Also I don't understand how it's possible for the attitude to develop an offset in flight, unless like LPC said, it was still relying on MAG data to determine its attitude ... although I thought the MAGs were only ever used to calculate heading?

Any pointers / shots in the dark are most appreciated.

Many thanks, David

[LPR]

David

I'm having the same problem with vibrations. I think the AQ with DIMU may be more sensitive to vibration caused by larger props. My quad with 11" props, flies well using the same AQ board, even if the props are not in perfect balance.

I used a tight string to reduce the vibrations by going around all the motors and then I can have an ok flight.
Reducing Tilt Angle D from 290 down to 150 makes my octo fly, but not well without the string.
With the string, default PIDs work.

I've tried the AQ board on a quad with four U8 motors and 29" props and I have the same problem with vibrations.
All the 29" props were very carefully balanced.

Try using a string to reduce vibration.

Larry

[hogster]

Hi Larry,

Thanks for your reply. In a way I'm glad to hear I'm not the only one struggling! Although I'm surprised that something as advanced as the AQ is not able to handle the vibrations better. It would be great if one of the developers could chime, particularly with regards to the HUD attitude discrepancy – surely the algorithms should never allow that to happen?

Are you also seeing this HUD attitude discrepancy? Could you post an example of the vibrations you're seeing on your platform?

I might as well try mounting the AQ on some rubber dampers, in lieu of not knowing what else to try! I would rather not try the string idea, as although it might work, I'm using the AQ on a professional aerial photography platform, and I don't think attaching a piece of string each time I unpack the vehicle and unfold the arms will give the right impression!

Many thanks for your feedback LPR, it's much appreciated.

David

[LPR]

David

I would try the string just as a way to be sure all your problems are being caused by vibrations.
I need more ESC to do more testing on the octo but I've flown with with 7 good ESC and one that was only 50%. ESC32 V3 will be come soon I hope.
I flew with four motors removed and had the same problems but with all the props very well balanced in no wind as a quad it flew well. When I add the string, wind was not a problem. I'm using Vulcan arms and it could be the 1.5 mm x 3 mm rectangular tubing is to blame but the arms are short for an octo frame. The center plates are 18" in diameter.
If building these MR was easy I would have no interest in doing it.

Larry

[hogster]

"If building these MR was easy I would have no interest in doing it."

That's a fair point! I too love the building and designing side of modelling almost more than the flying, but it can become quite tiring and disheartening when nothing you do seems to solve a persistent problem. I guess it's also different now that I'm using these platforms to pay my bills ...

How did you tie the string around your booms? Just one loop touching on all the ends of the booms, or single threads putting tension between each pair of arms?

Many thanks David

[Max]

Make sure the DIMU board is firmly seated in the sockets. I actually added a bit of hot glue on the connectors since I could wiggle the board a tiny bit while it was plugged in.

I'm about to put my older PWM/PID-based quad (Hairy) back in the air with DIMU. It flew well with AIMU and 6.7, so we'll see how that goes. If you have calibration data for your AQ6 board, you could try reverting to 6.7/AIMU to get a baseline. I don't think PWM outputs with non-ESC32s are very well tested in recent firmwares.

-Max

[hogster]

Hi Max,

Thanks for your reply

I will check the seating of the DIMU. I also applied hot-glue when mounting the DIMU as I didn't want it to work loose, but it won't harm to check it again

I could revert to the AIMU/6.7 although I would like to try all other options first – there seem to be so many advantages to the DIMU that I would like to keep using it if at all possible!

Do you know how the calculated attitude (eg. the HUD) could deviate from the actual attitude? The offset seems to be quite stable once it kicks in which is weird – I would have thought it would either be spot on, or completely wrong ...?

Many thanks for your help David