Discussion on IMU Calibration, level surface required, why?

[Traveler]

I wanted to start a discussion on the value of having a level surface for calibrating the IMU.

Let me start by saying I have always used a level surface to calibrate the IMU. Why, because that's what every video, (except DJI tutorial) I ever watched said to do, and that's what every person on the forum has said too. However, I can't find any documentation from DJI to backup this practice. Even the DJI tutorial video simply says to place the aircraft on "dry and plain ground". "Plain Ground, could this be a term to indicate level ground or surface? I couldn't find any reference for to such a use of terminology.

Because DJI does not call for a level surface for an IMU calibration, it has me pondering if the calibration is to establish the values between the different angles that are obtained during the process, vs angles in relationship to a level surface.

Having said all the above, I can see some logic in wanting a level surface, but if it was truly needed, why doesn't DJI say that!

So, for this discussion, I would like to know:

Has any member ever tried an IMU calibration while knowing they were not using a level surface, or inadvertently calibrated on a non level surface, and if yes, how did the aircraft perform?

THIS IS FOR DISCUSSION PURPOSES ONLY, I AM NOT ASKING ANY MEMBER TO BE A GUINEA PIG!

 

[Nate-xt]

when i don't use a near perfectly level ground to calibrate the IMU my gimbal is always off and it feels like something isn't right. never tried it on really really unleveled ground though.

 

[Traveler]

when i don't use a near perfectly level ground to calibrate the IMU my gimbal is always off and it feels like something isn't right. never tried it on really really unleveled ground though.

So your saying that if you have a IMU calibration on non level surface, doing a gimbal calibration on a level surface will not keep the gimbal level.

Interesting!

Beyond a tilted gimbal, would the bird fly straight?

Thank you for the data.

 

[Walt Rush]

When you do an IMU calibration you are telling the aircraft's attitude control system what "straight & level" should look like. If you do it on an un-level surface the aircraft will try to assume that same tilt as "straight & level but that induced tilt will make the aircraft wander in the air since it will believe that it is straight & level and hovering in place.

 

[Mr. Salty]

DJI's own tutorial video DOES call for a flat and level surface, as does the dialog box during the IMU calibration procedure in the Go app:

 

[Traveler]

DJI's own tutorial video DOES call for a flat and level surface, as does the dialog box during the IMU calibration procedure in the Go app:

I must have missed that message, I had only recalled the term I posted above, "dry and plain ground". Honestly it was that terminology that got me to thinking about why they didn't ask for a level surface.

With regard to the videos, I have seen many and 99% of them state what you said, a level surface, but I specifically watched the DJI video and they made no reference to it.

I do appreciate the responses, and this was not meant to insinuate that we have all been doing it wrong, but I wanted to know about the affects beyond just having a gimbal off tilt.

I think about it like this, if the bird tilted because of a bad IMU, then it would try to drift, but GPS would show a change and right/hold the bird into position, thus countering any issue of a off tilt bird.

Good data, thanks

 

[Mr. Salty]

I specifically watched the DJI video and they made no reference to it.

Not to argue, but if you're talking about the official DJI tutorial video I posted above, he quite emphatically does make the point that the IMU calibration must be done on a perfectly flat and level surface. It's at 1:20 in the video.

 

[Traveler]

Not to argue, but if you're talking about the official DJI tutorial video I posted above, he quite emphatically does make the point that the IMU calibration must be done on a perfectly flat and level surface. It's at 1:20 in the video.

There is no argument and I wouldn't take offense to any information. We clearly are just not watching the same video. The video I watch covered all aspect from compass to gimbal and it was vague on the IMU. I am glad there is a better one available.

When I started this discussion I said, I have always used a level surface, but that DJI does not state its value as I would expect and this gave me cause to question its importance. I wanted to collect data from others who have proven this hypothesis or disproven it. I can see the logic in being level, but with I can also see how the gps position kind of makes a possible tilt from a " bad calibration". moot.

More to the point, I have read many post where some members are always having gimbal problems while others enjoy problem free flights. So I decided to do my own testing to try to find out why. The IMU seamed like a good place to start, but I wanted to collect some data on how the bird would react to calibrating on a less than level surface.

My next phase was going to be testing the environment where the calibration occurs. Indoors, where most of us calibrate vs outdoors. Why, because I wanted to try to discover what's so different in our calibrations that had one user having the problems that another user does not.

I concede that level is correct vs not, which now brings me to consider environment.

You have read the manual, can we really trust DJI to tell us all we really need to know.

I do appreciate the feedback.

 

[jason]

There is no argument and I wouldn't take offense to any information. We clearly are just not watching the same video. The video I watch covered all aspect from compass to gimbal and it was vague on the IMU. I am glad there is a better one available.

When I started this discussion I said, I have always used a level surface, but that DJI does not state its value as I would expect and this gave me cause to question its importance. I wanted to collect data from others who have proven this hypothesis or disproven it. I can see the logic in being level, but with I can also see how the gps position kind of makes a possible tilt from a " bad calibration". moot.

More to the point, I have read many post where some members are always having gimbal problems while others enjoy problem free flights. So I decided to do my own testing to try to find out why. The IMU seamed like a good place to start, but I wanted to collect some data on how the bird would react to calibrating on a less than level surface.

My next phase was going to be testing the environment where the calibration occurs. Indoors, where most of us calibrate vs outdoors. Why, because I wanted to try to discover what's so different in our calibrations that had one user having the problems that another user does not.

I concede that level is correct vs not, which now brings me to consider environment.

You have read the manual, can we really trust DJI to tell us all we really need to know.

I do appreciate the feedback.

There's a lot the Chinese do not mention in plain english simply because they write their own technical manuals instead of hiring someone who has the technical knowledge of the english languish to do it for them.

 

[Fester]

There's a lot the Chinese do not mention in plain english simply because they write their own technical manuals instead of hiring someone who has the technical knowledge of the english languish to do it for them.

This was evident in the one email question about the new revision of the Phantom 4 Prop Hubs. It loses ALOT in translation, both ways...

As to the IMU of any aircraft, the calibration of the IMU sets the aircraft's Reference Artificial Horizon. If the calibration is not on a measured level surface the drone will begin to drift horizontally when hovering (which causes constant small position corrections to maintain its GPS position, i.e. more battery drain), and basically the same thing during straight and level flight. Without testing its hard to say just how much of a difference this may make, but I'm pretty sure that even 15-30 seconds of extra flight time might make all the difference between having your bird safely back home, or "re-kitting" itself.

 

[jason]

This was evident in the one email question about the new revision of the Phantom 4 Prop Hubs. It loses ALOT in translation, both ways...

As to the IMU of any aircraft, the calibration of the IMU sets the aircraft's Reference Artificial Horizon. If the calibration is not on a measured level surface the drone will begin to drift horizontally when hovering (which causes constant small position corrections to maintain its GPS position, i.e. more battery drain), and basically the same thing during straight and level flight. Without testing its hard to say just how much of a difference this may make, but I'm pretty sure that even 15-30 seconds of extra flight time might make all the difference between having your bird safely back home, or "re-kitting" itself.

I am fully aware of how the IMU needs to be setup on a level surface been doing this since March 2014 so i'm not new to this.

My statement regarding technical manuals written by the Chinese been poorly written simply because of their poor understanding of the English languish. This not a new problem for them as its been on going for many years. If you have ever had the chance to communicate with a manufacture in China you'd understand Guess there are many here who have had conversations with DJI technicians know exactly what i mean.