Dangers of taking off before GPS Satellites have all hooked up?

[N017RW]

It seems the analysis, so far, differs from the operator's account as told by the OP.

This is not a 'dig" at either of them.

 

[BudWalker]

Thanks so much for this info Budwalker!!! The .dat file is posted above.

As @msinger observed, that is not the right .DAT. There is no motor Start.. Look here for help on picking the right .DAT.

 

[Great Pumpkin]

Sounds like a compass error from lauching off a metal surface. The wild left hook is legion among compass errors of the past. I've seen it, and covered it, like Allstate!

I agree. Exactly the same thing happened to me when naively I took off from a manhole cover (never again), only somehow the AC recovered just before it was set to go into a tree.

 

[rodgerbwg]

I have a friend who had a crash today with his P4 Pro. He had to get up quick on a job so he took off before it had locked onto enough satellites to give the green bar and home point set. He is in P mode at takeoff btw. But he claims he does this quite often and has never had a problem. But today as soon as it got maybe 35 ft in the air and hooked up to enough satellites it just takes off left right into a tree and fell to its death. Any ideas on what may have happened in this case? I have never taken off until I got the home point recorded message for the app. I'm just wondering how you would know if your IMU was even all booted up and ready to work right if you don't wait for the green ready bar!

Interesting post and this happened to me a couple of days ago but I didn't crash as I was in an open field. It was cold , in the low 40's and I fired up the P4P and took off going up and away and the P4P was very erratic and then I got the Homepoint updated message and it straightened out. I'll wait from now on.

 

[sar104]

Interesting post and this happened to me a couple of days ago but I didn't crash as I was in an open field. It was cold , in the low 40's and I fired up the P4P and took off going up and away and the P4P was very erratic and then I got the Homepoint updated message and it straightened out. I'll wait from now on.

Erratic (what does that mean?) , or just responding in ATTI mode?

 

[CFzone]

I had the same thing too. I almost lost my drone, but luckily I was able to stabilize it before it crashed.

 

[CFzone]

I also calibrate my compass every time I fly , but I have had no crashes.

 

[GadgetGuy]

I also calibrate my compass every time I fly , but I have had no crashes.

That's the best way to introduce a bad compass reading, which may lead to crashes! After a good compass calibration, leave it alone!

 

[BudWalker]

That's the best way to introduce a bad compass reading, which may lead to crashes! After a good compass calibration, leave it alone!

I'm going to have to disagree. IMHO, the risk of getting a flawed compass calibration is way, way over stated. AFAIK, there has never been a documented case of a flawed compass calibration. If there is a problem the calibration will be rejected and the "interference detected, move to a better location" warning is issued.

 

[GadgetGuy]

I'm going to have to disagree. IMHO, the risk of getting a flawed compass calibration is way, way over stated. AFAIK, there has never been a documented case of a flawed compass calibration. If there is a problem the calibration will be rejected and the "interference detected, move to a better location" warning is issued.

It is a completely unnecessary risk to assume, when there is absolutely no benefit to additional compass calibrations after the first good one, unless you have been warned that it needs to be recalibrated. There are legions of documented cases of flawed compass calibrations, leading to crashes. I have personally experienced them! Only recently have the apps given any warning such as you describe. If you find the warning so dependable, why bother with your recalibration, in the first place, every time you fly?

 

[BudWalker]

There are legions of documented cases of flawed compass calibrations, leading to crashes. I have personally experienced them!

Legions? Can you show me one? But, with at least some compelling evidence that a flawed calibration was obtained. I've made an effort to see if a documented case exists. I often get the .DAT or several .DATs. In each case the previous calibration was several flights prior. That demonstrates the calibration was valid.

What I have seen a lot of is the claim that no proof is required since it's happened so many times.

Only recently have the apps given any warning such as you describe. If you find the warning so dependable, why bother with your recalibration, in the first place, every time you fly?

I don't calibrate every time before I fly. In fact I didn't calibrate my new Mavic until it was about 9 months old. I wanted to know if the magnetometers had drifted. In fact, they had drifted and that calibration did have a measurable positive effect that could only be seen by looking at the magnetometer data in the .DAT. I suspect that Mavic had a long way to go before an incident would have resulted from the magnetometer drift.

I do agree that a calibration isn't required unless directed to do so by the Go App. But, doesn't this mean that the current calibration is valid if the Go App doesn't say a calibration is required. Further, if a flawed calibration is possible then the Go App will say so and, I believe, prevent a flight from taking place.

 

[GadgetGuy]

Legions? Can you show me one? But, with at least some compelling evidence that a flawed calibration was obtained. I've made an effort to see if a documented case exists. I often get the .DAT or several .DATs. In each case the previous calibration was several flights prior. That demonstrates the calibration was valid.

What I have seen a lot of is the claim that no proof is required since it's happened so many times.

I don't calibrate every time before I fly. In fact I didn't calibrate my new Mavic until it was about 9 months old. I wanted to know if the magnetometers had drifted. In fact, they had drifted and that calibration did have a measurable positive effect that could only be seen by looking at the magnetometer data in the .DAT. I suspect that Mavic had a long way to go before an incident would have resulted from the magnetometer drift.

I do agree that a calibration isn't required unless directed to do so by the Go App. But, doesn't this mean that the current calibration is valid if the Go App doesn't say a calibration is required. Further, if a flawed calibration is possible then the Go App will say so and, I believe, prevent a flight from taking place.

We are in agreement on everything, except that compass errors have historically been a major cause of the wild left hook crashes upon takeoff, and I should know, because I had one with my second P3P, and thoroughly researched it. I had been launching from a wooden table top, which had a concealed steel frame, including a metal fire pot underneath, without any indication of a problem in DJI GO. I learned to check that the displayed compass direction of the aircraft nose in the app comports with reality before taking off. When there is a compass error that can lead to a wild left hook crash, it will not.

I confused you with the other poster who was calibrating the compass before every flight, and boasting he hadn't had a crash yet. I, too, have stopped calibrating the compass on new aircraft, unless the compass heading is clearly off. The newer versions of GO and GO 4 and the dual compasses and dual IMU's in newer aircraft have indeed successfully worked around most of the historical compass errors that led to crashes.

 

[BudWalker]

We are in agreement on everything, except that compass errors have historically been a major cause of the wild left hook crashes upon takeoff, and I should know, because I had one with my second P3P, and thoroughly researched it. I had been launching from a wooden table top, which had a concealed steel frame, including a metal fire pot underneath, without any indication of a problem in DJI GO. I learned to check that the displayed compass direction of the aircraft nose in the app comports with reality before taking off. When there is a compass error that can lead to a wild left hook crash, it will not.

I confused you with the other poster who was calibrating the compass before every flight, and boasting he hadn't had a crash yet. I, too, have stopped calibrating the compass on new aircraft, unless the compass heading is clearly off. The newer versions of GO and GO 4 and the dual compasses and dual IMU's in newer aircraft have indeed successfully worked around most of the historical compass errors that led to crashes.

Well I'm a little confused about what you're saying. But, the incident you described was caused by the steel frame distorting the geomagnetic filed. I'm not sure I'd call that a compass error or malfunction - it's certainly not a calibration issue. In that incident the magnetometers are giving accurate measurements. Better, more accurate, redundant magnetometers, dual IMUs, etc wouldn't have made any difference. Also, a calibration in a different location wouldn't have made any difference.

I've been saying for some time that the single most effect method to prevent launch time fly aways is to make sure the red triangle heading indicator in the Go App is consistent with the actual AC heading.

Hasn't the Go App always alerted the pilot to "magnetic interference" problems while calibrating? I did some tests, I think 2 years ago, where I tried to obtain a bad calibration by doing it next to my truck. I couldn't get close enough to the truck to get a bad calibration without getting that error message.

I did manage to get a bad calibration by attaching an allen wrench to the leg next to the compass. After calibrating in that configuration I then removed the allen wrench and that produced an AC with a bad calibration. But, that's cheating isn't it?

 

[sar104]

Well I'm a little confused about what you're saying. But, the incident you described was caused by the steel frame distorting the geomagnetic filed. I'm not sure I'd call that a compass error or malfunction - it's certainly not a calibration issue. In that incident the magnetometers are giving accurate measurements. Better, more accurate, redundant magnetometers, dual IMUs, etc wouldn't have made any difference. Also, a calibration in a different location wouldn't have made any difference.

I've been saying for some time that the single most effect method to prevent launch time fly aways is to make sure the red triangle heading indicator in the Go App is consistent with the actual AC heading.

Hasn't the Go App always alerted the pilot to "magnetic interference" problems while calibrating? I did some tests, I think 2 years ago, where I tried to obtain a bad calibration by doing it next to my truck. I couldn't get close enough to the truck to get a bad calibration without getting that error message.

I did manage to get a bad calibration by attaching an allen wrench to the leg next to the compass. After calibrating in that configuration I then removed the allen wrench and that produced an AC with a bad calibration. But, that's cheating isn't it?

Agreed. The effect of a bad calibration is that the aircraft won't be stable and will likely drop into ATTI if it stays aloft after taking off from a good location. Taking off from a bad location (magnetically) doesn't require a bad calibration to cause problems.

 

[GadgetGuy]

Well I'm a little confused about what you're saying. But, the incident you described was caused by the steel frame distorting the geomagnetic filed. I'm not sure I'd call that a compass error or malfunction - it's certainly not a calibration issue. In that incident the magnetometers are giving accurate measurements. Better, more accurate, redundant magnetometers, dual IMUs, etc wouldn't have made any difference. Also, a calibration in a different location wouldn't have made any difference.

I've been saying for some time that the single most effect method to prevent launch time fly aways is to make sure the red triangle heading indicator in the Go App is consistent with the actual AC heading.

Hasn't the Go App always alerted the pilot to "magnetic interference" problems while calibrating? I did some tests, I think 2 years ago, where I tried to obtain a bad calibration by doing it next to my truck. I couldn't get close enough to the truck to get a bad calibration without getting that error message.

I did manage to get a bad calibration by attaching an allen wrench to the leg next to the compass. After calibrating in that configuration I then removed the allen wrench and that produced an AC with a bad calibration. But, that's cheating isn't it?

Agreed again on all, and kudos on that red triangle heading indicator! It saved my bacon, many a time in the past! My main point was that compass calibrations in areas that cause compass errors will inevitably lead to problems, and once calibrated properly, the compass calibration should never be repeated before every flight, as the earlier poster was bragging about doing. If the compass calibration is done in an area of any magnetic interference, it may or may not cause the calibration to fail. The Go App keeps getting better and better, but it is not infallible, and it has been less robust historically. Best to thoroughly know the area you are calibrating in once, and then not have worry about what might be lurking under the surface at every new unknown location that might be unseen, were one to follow the misguided advice to calibrate before every flight! Calibrate once, properly, in a good location, and leave it alone, unless you have a very good reason to believe it needs recalibrating.

 

[RémyHeli]

Also, a calibration in a different location wouldn't have made any difference

There is actually but very tiny. I had posted in this forum a picture showing magnetic north vertical stripes, looking similar to time zones differences. Different location meaning same country or another has no impact for drone usage, most important being non distorted magnetic field. I would not fly over celtic monuments or massive stones that could possibly contain lot of iron..

I wonder if putting the craft close to speakers would ´gauss' the compas forever?

Interestingly there is slow changes in the planet's molten core, which contains liquid iron, causing magnetic north to shift over years which requires long living animal to recalibrate their instinct.

Adjust your compass now: the north pole is migrating to Russia

 

[BudWalker]

There is actually but very tiny. I had posted in this forum a picture showing magnetic north vertical stripes, looking similar to time zones differences. Different location meaning same country or another has no impact for drone usage, most important being non distorted magnetic field. I would not fly over celtic monuments or massive stones that could possibly contain lot of iron..

I wonder if putting the craft close to speakers would ´gauss' the compas forever?

Interestingly there is slow changes in the planet's molten core, which contains liquid iron, causing magnetic north to shift over years which requires long living animal to recalibrate their instinct.

Adjust your compass now: the north pole is migrating to Russia

Declination is not detected and then compensated for by a calibration. It can't be since it's an effect that doesn't rotate with the AC; it's external to the AC.

Declination is actually derived from GPS coords after there are a sufficient number of satellites.

 

[BudWalker]

Agreed again on all, and kudos on that red triangle heading indicator! It saved my bacon, many a time in the past! My main point was that compass calibrations in areas that cause compass errors will inevitably lead to problems, and once calibrated properly, the compass calibration should never be repeated before every flight, as the earlier poster was bragging about doing. If the compass calibration is done in an area of any magnetic interference, it may or may not cause the calibration to fail. The Go App keeps getting better and better, but it is not infallible, and it has been less robust historically. Best to thoroughly know the area you are calibrating in once, and then not have worry about what might be lurking under the surface at every new unknown location that might be unseen, were one to follow the misguided advice to calibrate before every flight! Calibrate once, properly, in a good location, and leave it alone, unless you have a very good reason to believe it needs recalibrating.

But, you still have not offered any reason to think that flawed calibrations happen. Your description of your incident makes it clear that incident was caused by a geomagnetic distortion at the launch site. It was not caused by a flawed calibration.

I'd like to embellish some on a point I made previously. The advice that it's risky to calibrate often is usually justified by saying that the Go App will instruct you to do so if necessary. But, this leads to a logical inconsistency. If an unnecessary calibration causes a flawed calibration then it will be caught on the next attempt to fly. If it's not caught then that means that the pilot won't always be warned that a calibration is necessary. And, therefore calibrating even when there are no instructions to do so is a good idea.

Let me finish by adding that I don't calibrate before every flight. I also don't use a lucky rabbits foot to ensure safe flight. But, I don't see any risk if others do so.

 

[Lutrent]

I recalibrate my compass every flight in new areas call me crazy but I never have any problems ever

Im a newbie and I have read that too many times. Calibrate Compass for every flight. Nothing is too important that I cant do my flight checks before hand...

 

[GadgetGuy]

But, you still have not offered any reason to think that flawed calibrations happen. Your description of your incident makes it clear that incident was caused by a geomagnetic distortion at the launch site. It was not caused by a flawed calibration.

I'd like to embellish some on a point I made previously. The advice that it's risky to calibrate often is usually justified by saying that the Go App will instruct you to do so if necessary. But, this leads to a logical inconsistency. If an unnecessary calibration causes a flawed calibration then it will be caught on the next attempt to fly. If it's not caught then that means that the pilot won't always be warned that a calibration is necessary. And, therefore calibrating even when there are no instructions to do so is a good idea.

Let me finish by adding that I don't calibrate before every flight. I also don't use a lucky rabbits foot to ensure safe flight. But, I don't see any risk if others do so.

Had I "successfully" calibrated the compass where the geomagnetic distortion caused the crash, that compass calibration would have been flawed. At that time, the app was not as robust as it is today. I have't had a problem since then, as I am better, the app is better, and the aircraft is much better! These types of anomalies were very common with the early Phantoms.

As to your embellishment, I do not justify the advice that it is risky to calibrate often, by saying that the Go App will instruct you to do so if necessary, for the very reason you cite. I justify it, instead, based upon the logic that unless you have good reason to believe the calibration is off (which may include an app warning), leave your last known good compass calibration alone! I would liken it to an IMU calibration on a perfectly level surface, measured with an electronic level, compared to recalibrating your IMU before every flight on what appears to be level ground.

Each to their own. If nothing else, eliminating the "compass dance" before every flight saves time, and avoids the attention of the men in white coats who think you are crazy, and are taking you into 72 hour protective costody for your own good!