To Those Who've Experienced Compass Errors.....

  • Like
Reactions: CRCs Reality
The ordering of the columns isn't relevant and has no effect on the values or their accuracy. The values in a row all occur at the same time. Every converter that you've seen and any converter you will see works this way

I must have missed this post. :cry: I read the quoted response above, and it's as if I didn't know what I was talking about and basically wasted a lot of time trying to point something out.

I originally brought it up because I had always known the values to not be the same in each column when written. At least not in a data logger setting anyhow. My question to you was based on what I knew, and what kind of effect you thought it would have on the accuracy of the tools you created.

I attached a file that starts out with the 1st 6 column's being dedicated to 3 sets of the same Longitude and Latitude data. You'll notice that system struggles at the beginning as column's 5 & 6 do not start writing the data until row 237. It's best to compare the column's on the same row when the Aircraft is moving. I believe at row 440 the Aircraft is moving around 14mph. Look it over when get some time and see what you think.
 

Attachments

  • BudWalker.zip
    18.7 KB · Views: 167
I must have missed this post. :cry: I read the quoted response above, and it's as if I didn't know what I was talking about and basically wasted a lot of time trying to point something out.

I originally brought it up because I had always known the values to not be the same in each column when written. At least not in a data logger setting anyhow. My question to you was based on what I knew, and what kind of effect you thought it would have on the accuracy of the tools you created.

I attached a file that starts out with the 1st 6 column's being dedicated to 3 sets of the same Longitude and Latitude data. You'll notice that system struggles at the beginning as column's 5 & 6 do not start writing the data until row 237. It's best to compare the column's on the same row when the Aircraft is moving. I believe at row 440 the Aircraft is moving around 14mph. Look it over when get some time and see what you think.
Looks to me like they are different Longitude and Latitude data
upload_2016-8-5_15-4-33.png
 
Compass error and GPS error are not the same thing.
....

There not the same thing, but affect P-GPS and RTH modes. With compass error, GPS is useless.

Switching to Atti, is the best solution.

BUT, all pilots have to practice Atti mode. Take a blade nano qx or an XK X100 and practice @ your living room (and your garden).

DJI pilots seems to be the most unskilled ones, when it comes to fly manual mode. :rolleyes:

How many videos have you seen, with someone flying with descent skills, a dji product? (Sure there are, but the vast majority of videos are showing people without ANY skills). That is NOT the case when you see members of the RCgroups flying their machines...

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.
 
Last edited:
Stop calibrating the compass before every flight. It is not necessary. You are introducing errors when you do this. When you get a good calibration, leave it.

Exactly how do you induce errors & what actually causes the errors
 
magYaw is derived by first computing a vector based on the x, y and z magnetometers. In general, that vector doesn't lie in the xy plane due to the geomagnetic inclination and the roll and pitch of the AC. Using quaternion math that vector is then rotated into the xy plane by using the values of roll and pitch coming from the FC.

magYaw and Yaw will have (close to) the same value unless one of them is incorrect. At batteryOn Yaw gets set to something like magYaw. After that Yaw relies mostly on the IMU sensors (particularly the gyros) and the calculations done by the FC. If the magnetometers are compromised at batteryStart (like launching from a man hole cover) then the incorrect magYaw value will be what initializes Yaw. After launch magYaw becomes correct because the man hole cover is no longer close enough to cause a problem. BUT, Yaw continues to have the incorrect value because while magYaw has been correcting there hasn't been any rotation about the Z axis. This is what happened in the 2 example flights.

Just to be clear magYaw doesn't come from the P3, it comes from a calculation that DatCon does. It's a diagnostic that's useful when the Yaw value is suspect. The P3 may have it's own magYaw look-alike or something similar that's used to detect compass errors.

I didn't understand your second question.
To clarify, are you saying that if the Phantom is turned on in an area of high magnetic deviation, it gives a bad Magyaw value? Or does that happen only at motor start? The reason I ask is I've often turned on my battery while sitting on something causing lots of magnetic interference, but I would then hold the phantom above my head while watching the compass bias values. Once it read between 1400-1600 I'd select auto take off and release from my hand. So far I haven't had any issues, but maybe I'm lucky if all references are stored at battery on initialization and not at motor start?
 
To clarify, are you saying that if the Phantom is turned on in an area of high magnetic deviation, it gives a bad Magyaw value? Or does that happen only at motor start? The reason I ask is I've often turned on my battery while sitting on something causing lots of magnetic interference, but I would then hold the phantom above my head while watching the compass bias values. Once it read between 1400-1600 I'd select auto take off and release from my hand. So far I haven't had any issues, but maybe I'm lucky if all references are stored at battery on initialization and not at motor start?
I believe the question is when does Yaw get set with the magYaw value. I don't actually know. If you provide a .DAT from one of those flights we could determine that. Your procedure is the experiment that I would do to determine this.
 
Looks to me like they are different Longitude and Latitude data

Ok then so you might have a different opinion about your quote below? If so, wouldn't you now agree it might be better for those columns with formulas being used for diagnostics tools be placed next to each other?


The ordering of the columns isn't relevant and has no effect on the values or their accuracy. The values in a row all occur at the same time. Every converter that you've seen and any converter you will see works this way
 
Exactly how do you induce errors & what actually causes the errors
If you get a good compass calibration at location A and the craft flies great and there are no problems, then leave that calibration. There is no need to redo it every flight unless you travel hundreds of miles from location A, the declination does not change enough to matter.
If you calibrate before EVERY flight, say you had a working calibration at location A and go to a new location and calibrate again, but this time you have some interference, maybe minor but enough to cause errors. This would be where the errors are introduced. You went from having a perfectly good calibration to re calibrating and having one not so accurate.
 
  • Like
Reactions: Yiannis.B
There is no need to redo it every flight unless you travel hundreds of miles from location A, the declination does not change enough to matter.

So what if the compass becomes contaminated between flights, and in your case you wouldn't know about it until you are already in flight. In this type of situation people become numb and never think to pay any attention to the compass and before they know they're in a predicament.

If you want to make a reason for it to fail, it will fail. But if you know how to properly calibrate the compass, you are likely to never have any issues from calibrating prior to each flight. I have done so now over 400 flights on the P3P alone with each having the compass calibrated before flight. I have the flight logs to each flight and none show a compass error of any kind.

I have always taken compass calibrating seriously and have even went as far as doing what I feel like is the most accurate method by using the setup seen in the image below which rotates like a lazy susan. It works great when used on top of a plastic travel case.
P3table.jpg
 
I've had almost 30 flights with my P3A so far. Earlier today, after calibrating the compass before each flight, I took off from the mountain cliff right at sunrise to get some low cloud footage with the sun shining on it and flew for about 15 minutes and as soon as I landed, you guessed it, I realized I forgot to hit "record", so I immediately put a fresh battery in and flew again. About midway through the 2nd flight, that's when the compass problem began. The bird tilted left and I got a compass error, so I switched to A-mode briefly, then back to P. Bird steadied for a while then errored again a few minutes later, tilting the horizon to the left again. Repeated steps and it went back to normal. Took the bird up for a 3rd flight about an hour later and had no problems. So, questions are...

1) Is this typically what happens with those of you that have had compass errors?
2) Did you get your compass error after inserting a new battery and immediately flying again?
3) Perhaps the error occurred due to the bird still being warm after the previous flight?

It seems like an isolated incident, and healthydrones.com didn't show the compass errors to be in dangerous range.
If you want to see the area I was flying, see here
To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.
PS, I think the part where the quad tilted were edited out, but I thought showing the site I took off from might help.

To calibrate the compass before each flight is a huge mistake, I have not recalibrated in 4 months 100.s of flights
 
So what if the compass becomes contaminated between flights, and in your case you wouldn't know about it until you are already in flight. In this type of situation people become numb and never think to pay any attention to the compass and before they know they're in a predicament.

If you want to make a reason for it to fail, it will fail. But if you know how to properly calibrate the compass, you are likely to never have any issues from calibrating prior to each flight. I have done so now over 400 flights on the P3P alone with each having the compass calibrated before flight. I have the flight logs to each flight and none show a compass error of any kind.

I have always taken compass calibrating seriously and have even went as far as doing what I feel like is the most accurate method by using the setup seen in the image below which rotates like a lazy susan. It works great when used on top of a plastic travel case.
View attachment 61570


The software will likely inform you that you need to calibrate, Your IMU readings will indicate if you may have a problem Dont create problems that dont exist.
 
To calibrate the compass before each flight is a huge mistake, I have not recalibrated in 4 months 100.s of flights

Explain, how it is a Huge Mistake?
 
The software will likely inform you that you need to calibrate, Your IMU readings will indicate if you may have a problem Dont create problems that dont exist.

After losing 2 P2V+'s I began to calibrate the compass prior to each flight. I now roughly have 525 consecutive compass calibrations. All with Zero issues as well. No problems created, no huge mistakes in the process....just happy that I still my 1st and only purchased P3. I even used the same P3 when I was a DJI Product and P3 Beta Tester throughout 2015.

The only problem I ever experienced was app freeze up and tablet shut down when I 1st started beta testing. The compass related issues during and after being a tester took place with those that did not calibrate prior to flight. Not everyone, just those involved with a loss due to a compass issue.

Technically if flying from the same home point each flight you should not need to calibrate the compass. But as I say, I do and have never had any repercussions from doing it. Most likely it is because I know how to do the compass calibration properly. Or, maybe I'm lucky? Regardless of luck, I've proven to myself that properly calibrating the compass prior to each flight is not a Huge Mistake.
 
I wouldn't say it is a huge mistake. More like waste of time

No its worse than a waste of time; chances are one day you will calibrate somewhere with a local magnetic anomaly, and once you are high/far from the anomaly, your bad calibration will come back to bite you.
 
  • Like
Reactions: Yiannis.B
If you check the mod value after a calibration, and it is within the normal values - that should prevent you from taking off with a bad calibration. Yes? Maybe?

I've done both - been compulsive about calibration and forgot about it. Other than the brief 'outages' we are discussing here, I've not had a problem. It is possible that anyone who does calibrate early and often has figured out how to do and doesn't introduce errors. But who knows? I think that the brief outages are a NOT due to a bad calibration. That should rocket the craft out of control quickly as opposed to the seemingly random and brief interruptions we see here.

As is typical, we are flying blind due to DJI's intransigence. I wouldn't hurt them too much to actually produce a white paper about it.

It is most likely a firmware value that got tweaked too far.

Or it's Aliens.
 
If you check the mod value after a calibration, and it is within the normal values - that should prevent you from taking off with a bad calibration. Yes? Maybe?

No, not necessarily. Depends what you call bad calibration; the calibration might in fact be "good" right where you did it, but only there, and not 3 miles further. I dont think that necessarily shows in the mod values (which I understand to be a 3 axis averaged offset).
 
Could you explain why in this case selecting RTH is a bad idea?

Also what could and would happen if say a compass error took place and the pilot then selected RTH, what might the pilot prepare for if RTH was in fact selected?
RTH needs the compass to get a correct heading to the Home Point.
 
  • Like
Reactions: Yiannis.B
No, not necessarily. Depends what you call bad calibration; the calibration might in fact be "good" right where you did it, but only there, and not 3 miles further. I dont think that necessarily shows in the mod values (which I understand to be a 3 axis averaged offset).

Your statement implies that you can calibrate a compass successfully in an environment that has some local effects (ie, rebar) and still have acceptable mod values. And that you should calibrate pretty much at every flight.

Do you have any actual experience or knowledge about this? I suppose one could walk around with the RC and drone and watch the mod values change but my neighbors think I'm weird enough as it is.

Might have to take a walk in the woods. I could pretend I was dousing.
 

Members online

No members online now.

Forum statistics

Threads
143,066
Messages
1,467,354
Members
104,933
Latest member
mactechnic