Accurate leveling for IMU / Gimbal Cals

Brockrock · Oct 21, 2016

After recently posting a pair of videos to demonstrate the virtues of Litchi ( Example of a Litchi mission for those on the fence... ), it became fairly apparent to me that I was one of the lucky ones with a tilted horizon issue on my P4... So, I began to dig for info, here, YouTube, and everywhere else.

Today, I downgraded the firmware on both my remote and copter, followed by reloading the latest on both. It went very smoothly, and this is one of the ways that some folks have rectified this issue, at least for awhile anyway, until it comes back again. One post that I read even stated that this is what DJI will have you do in some cases during trouble shooting and prior to finalizing an RMA.

I then set up to perform an IMU calibration and gimbal calibration, but prior to doing so, I placed a carpenter's level on the table that I have been performing these calibrations on. I had prior checked this surface to be level with my iPhone - like many no doubt do - and guess what...it was off on both the X and Y axes by at least 2 degrees. I took care of this and then performed the calibrations smoothly.

It was not a very good weather day here where I am, so sadly, I have yet to fly the copter, but the real point that I wanted to make is that using a carpenter's level to verify that your calibration area is level is a must. 2 degrees - in my case - is not much, but by the appearance of my videos, my horizon was off by 2 - 3 degrees. I think that the iPhone - and other smart phones - is just not long enough to give an accurate reading of true level, and I'm glad that I checked this as I did.

alokbhargava · Oct 21, 2016

You are right iPhone leveling is not that accurate, to get good level settings, one needs min 10-12" level.

Sent from my iPhone using PhantomPilots

GMack · Oct 21, 2016

I found my little round bubble level was off a bit compared to the longer carpenter's level too. Maybe 1/4 bubble difference or maybe 1 degree? Outcome I've been fighting is the start ground level is zero, but at the end of maybe a mile of flying it ends at -50 feet or some negative AGL number. Nose was pointing down about 1/4 bubble which maybe was the issue against the longer level.

Today the start and end were the same at zero feet after a mile or so flying. It also auto landed by itself in RTH as battery had about 30 seconds left and RC was beeping like mad and I had to fight between it and manual control, although it went down harder than I normally land manually as it seemed to be persistent in doing the RTH by itself.

Brockrock · Oct 21, 2016

GMack said:
Today the start and end were the same at zero feet after a mile or so flying. It also auto landed by itself in RTH as battery had about 30 seconds left and RC was beeping like mad and I had to fight between it and manual control, although it went down harder than I normally land manually as it seemed to be persistent in doing the RTH by itself.

Well, it sounds like you may have solved an issue that you were having today - which is always a good feeling - followed by that other good feeling that this hobby can give us. That intense, heart pounding excitement of a critically low battery...

...

dirkclod · Oct 21, 2016

We've been working with this leveling since the P2's and after all I have seen here and tried myself I ended up using a piece of glass taken from a
picture frame and playing cards with a level like alok mentions to do all mine . I turn the level every way on the glass I can and also make sure that glass is supported in the middle .
Now I got that glass from a picture of my mother-in-law then hung it back up . I'm still here so that tells ya my wife hasn't noticed

Now that fixed my not yawing like top on my P2V and have done it that way in the same spot ever since with my others ..
Just what I do .

Docjkm · Oct 25, 2016

Just makes sense, eh?

Erised · Oct 25, 2016

I calibrate my IMU and gimbal on a flat surface leveled within .001 of an inch, I have a machinist level. My horizon is still off some of the time, some times I fly all out and bank and all is well other times no, some time the wind shifts it then sometimes no. Flying side ways in the wind will push the gimbal and that's understandable because the force is greater than the gimbal motors, but hovering and it's off after just having calibrated the bird is frustrating, then I start to move and it levels off, I give up! It's not too bad and mostly level and I adjust in flight. I still think and hope firmware will be able to improve this condition. It's never consistent and that makes me think the problem is not mechanical. (I hope)

Peter Galbavy · Oct 26, 2016

I bought this especially for the P4 and it is cheap, light and small enough to carry in the same bag compartment as the props. I am sure similar things are available in your region: https://www.amazon.co.uk/dp/B0001P0TNM ("Made in Germany" with 0.5mm/1m accuracy)

Brockrock · Oct 26, 2016

All great comments and points. Thank you! Although the P4 if my first quad-copter, I have been closely watching DJI and this industry for many years with great interest. I have been aware that this horizon leveling issue was a recurring issue, and I had hoped that it had been rectified with the P4.

I looked at some of the original video footage and photos that I shot with my P4, and the horizon was perfectly level sometimes, and less than level others. There seems to be no pattern really, as sometimes the copter was hovering and taking a pic, and the horizon was off, and sometimes it was moving sideways on a Litchi mission into the wind, and it was perfectly level... I have also recently experimented with the C2 button / scroll wheel combination, and although it works, it does cause a noticeable twitch in the video footage.

I like the idea of using a piece of glass as a leveling surface - as mentioned by dirkclod above - and I now have a dedicated, 18"x18" piece of 1/4" glass that I am using for just that purpose...and, no mother-in-law involved...

...

Klnyc · Oct 26, 2016

Erised said:
I calibrate my IMU and gimbal on a flat surface leveled within .001 of an inch, I have a machinist level. My horizon is still off some of the time, some times I fly all out and bank and all is well other times no, some time the wind shifts it then sometimes no. Flying side ways in the wind will push the gimbal and that's understandable because the force is greater than the gimbal motors, but hovering and it's off after just having calibrated the bird is frustrating, then I start to move and it levels off, I give up! It's not too bad and mostly level and I adjust in flight. I still think and hope firmware will be able to improve this condition. It's never consistent and that makes me think the problem is not mechanical. (I hope)

yes i'm with u. when i panning side way my horizon are tilted. Like u said this caused by the force of wind.

klnyc

Patrick · Oct 26, 2016

dirkclod said:
We've been working with this leveling since the P2's and after all I have seen here and tried myself I ended up using a piece of glass taken from a
picture frame and playing cards with a level like alok mentions to do all mine . I turn the level every way on the glass I can and also make sure that glass is supported in the middle .
Now I got that glass from a picture of my mother-in-law then hung it back up . I'm still here so that tells ya my wife hasn't noticed
Now that fixed my not yawing like top on my P2V and have done it that way in the same spot ever since with my others ..
Just what I do .

agreed, i use the glass bed cover from my 3d printer then do the leveling with paper or playing cards, works great, seems like every surface in my house is out of level hehe so a small sheet of glass works the best for me!