My Latest Crash

[San2C]

I have to ask at this point, is there a rule of thumb in terms of distance and mass for avoidance of metal that throw the compasses off? Or do we just sort of wing it and hope for the best?

 

[Neon Euc]

I have to ask at this point, is there a rule of thumb in terms of distance and mass for avoidance of metal that throw the compasses off? Or do we just sort of wing it and hope for the best?

I would just say the further the better but my own personal experience I had a compass error at 170 metres before it fell so I have no idea to be honest

 

[sar104]

I have to ask at this point, is there a rule of thumb in terms of distance and mass for avoidance of metal that throw the compasses off? Or do we just sort of wing it and hope for the best?

Neither - I suggest that you follow the advice that I posted in #34; check that the aircraft orientation arrow on the map agrees with the actual direction the aircraft is facing. If it does then you are almost certainly not in an area of magnetic distortion. If it doesn't then don't take off - move the aircraft to another location and check again.

 

[btrussell]

One other possibility.... churches have been approached by cell service provider to host cell sites within their tall structures. This provides a hidden antenna platform for the providers and a revenue stream for the churches. Is it possible that this aircraft fell victim to EMI?

 

[sar104]

One other possibility.... churches have been approached by cell service provider to host cell sites within their tall structures. This provides a hidden antenna platform for the providers and a revenue stream for the churches. Is it possible that this aircraft fell victim to EMI?

No. If you are asking if it could interfere with the uplink control channel, then note that the behavior was not driven by control inputs. Other than that, the onboard systems are not going to be troubled by a few watts of cellular RF.

 

[Meta4]

I have to ask at this point, is there a rule of thumb in terms of distance and mass for avoidance of metal that throw the compasses off? Or do we just sort of wing it and hope for the best?

First, you don't need to be cautious of metal.
It's steel or iron and live electric cables that upset your compass but other metals have no magnetic effect.
2nd. The ability of a magnetic field associated with a piece of steel to affect your compass depends on the size of the steel object and how close it is to the compass.
Something the size of a pin would have to be very close to have any effect, but a steel bridge would have a larger magnetic field.

Even with large steel objects, the magnetic field does not extend to great distances.
There is about 100000 tons of steel here but flying at this distance is quite safe:

You can do some testing by descending slowly from above a steel roof.
When the Phantom is getting into the magnetic field of the roof, you'll find the Phantom wanting to wander and slowly spiral.
It's quite safe to experiment as climbing up out of the field will make things normal again.
You'll probably find the effect somewhere like 5-6 feet above the roof.

To go back to your question, my rule of thumb would be that if you are far enough away to photograph the whole bridge, tank, ship, etc there is no problem.
If you are in close enough to photo small parts of the bridge etc, then you may be too close.

Unless you fly very close to a large steel object, you have nothing to worry about in flight.
But your launch surface is a different issue.
The compass is down at the bottom of your landing gear to get it as far from the electrical activity in the Phantom.
If you place it on a steel surface (like a car roof) or on reinforced concrete, the compass could be just an inch away from a substantial magnetic field.
In concrete you never know how if the compass is one inch or 6 inches away.
Just steer clear of launching or landing on reinforced concrete.

I had a compass error at 170 metres before it fell

As explained above, no man-made object has a magnetic field that would have any effect on your Phantom at 170 metres.
Your mention that this was observed before a fall.
Compass errors don't stop the motors or cause the Phantom to fall.
It sounds like your compass error might have been during the fall, in which case the error would have been due to the compass recording the spinning of the Phantom at a faster rate than it can spin in controlled flight.

 

[San2C]

Neither - I suggest that you follow the advice that I posted in #34; check that the aircraft orientation arrow on the map agrees with the actual direction the aircraft is facing. If it does then you are almost certainly not in an area of magnetic distortion. If it doesn't then don't take off - move the aircraft to another location and check again.

Excellent. Thanks.

 

[tomtomtomtom]

Doesn't anyone think that as the craft got too close to the church, a bolt of lightning hit it, and you have been warned to stay away from HIS space!

 

[Rudder Bug]

It's really scary knowing that this things can suddenly turned into such behaviour. Knowing that ATTI in this situation might be salvageable measure to some extent makes me a little less worry.
But what use of ATTI if AC is only a spot in the sky after a few hundreds meters or even less than that and you not have the compass data to bring the bird home? At least you must know to which direction it is heading to.

Hi Andy,
This is something every pilot should practice: learn to fly that little dot in the sky. If it is moving away from you it appears to be descending. To confirm it, if you move the right stick to the right, the drone will go to the right. If you pull on the stick, your bird will get closer to you. If it is facing you, moving the stick to the right will make your drone move to the left. The way home is pushing on the stick. I learned that old trick while flying R/C models, which had no GPS nor compass and could not hover when in trouble.

I think we can gain a lot in practising flying on ATTI mode as often *** possible. But for sure, a strong wind can become your worst enemy and fast!

Fly safe.

Gilles

 

[lonjsnyder]

Excellent. Thanks.

And if you want to look for unseen metal below the surface of your take off area, try using a smart phone tesla meter
Here one for iOS:

Metal Detector / EMF Meter on the App Store

 

[Boefinator]

If it was a compass problem then switching to ATTI would have eliminated the problem.

That's how we train. We even simulate it for our pilots to train the ATTI reaction when there is a loss of control.

 

[Russ43Phantom]

The only time I experienced radical flight at take off was when I took off from a picnic table that had steel legs. The table was in the middle of a large field. The drone was unable to stabilize or hover immediately after takeoff. I had to fly it into the ground.

 

[svjobeth]

I've only experienced similar issues when flying around a boat repair yard. The AC was a bit wonky when near or between metal buildings. I didn't experience take-off/landing issues as I was able to set up away from the buildings. Otherwise, once I was well above the metal structures, things seemed normal.

I've seen crash videos where the AC suddenly went haywire in the air, often after several minutes of flight, sometimes clear of structures, other times nearby one or more structures - a multi-story building for example. In a lot of these cases, the pilots blamed the loss of control on metal influence from the take-off site. As the AC had flown normally from the take-off site, I'm not sure I understand why any metal on or around the area of take-off would influence the flight several minutes out.

 

[sar104]

I've only experienced similar issues when flying in a boat repair yard. The AC was a bit wonky when near or between metal buildings. I didn't experience take-off/landing issues as I was able to set up away from the buildings. Otherwise, once I was well above the metal structures, things seemed normal.

I've seen crash videos where the AC suddenly went haywire in the air, often after several minutes of flight, sometimes clear of structures, other times nearby one or more structures - a multi-story building for example. In a lot of these cases, the pilots blamed the loss of control on metal influence from the take-off site. As the AC had flown normally from the take-off site, I'm not sure I understand why any metal on or around the area of take-off would influence the flight several minutes out.

The reason that the effect can be delayed is related to the maneuvers performed, but it usually happens quite soon after takeoff. The flight logs generally reveal the problem though.

 

[GadgetGuy]

The only time I experienced radical flight at take off was when I took off from a picnic table that had steel legs. The table was in the middle of a large field. The drone was unable to stabilize or hover immediately after takeoff. I had to fly it into the ground.

Been there, done that, 3 years ago, with a P3P on early FW. I killed the motors to stop it from cartwheeling off the roof onto concrete, after it ran into the roof deck in a strong left hook immediately after launch from below. Luckily, only the props were damaged. The wooden table top I launched from concealed a metal firebowl and steel legs. Aircraft arrow pointer was facing the wrong direction before takeoff. Lessons learned!

 

[Kpa5]

San2C, hope all works out with DJI and your drone.

Lngjsnyder....You tend to scan your take off area with this app or do you leave it running during flight?

Would a landing pad like the one I have uploaded block EMI during takeoff and landing?

98% of the time I am taking off from some type of sports field...grass
A few times from parking lots and have not experienced EMI...yet.
I will start paying more attention to A/C orientation before takeoff.

 

[JSKCKNIT]

You were in P-GPS mode, also known as GPS-Atti mode, not ATTI mode. That means that the FC is attempting to control the aircraft location - holding position when sticks are centered or holding track according to heading and elevator/aileron inputs. So it is combined pilot/FC control.

The compass error affects the FC control because the FC has incorrect information on the aircraft heading, and so corrections to maintain position or heading don't have the expected outcome - it applies thrust in the wrong direction.

Depending on the magnitude of the compass error, that can result in various uncontrolled flight patterns, including the toilet bowl spiral that you observed. The error also shows up clearly in the increasing discrepancy between the IMU-computed position vs. the actual GPS location as the flight progresses:

View attachment 96906

If you switch to ATTI mode then the FC stops trying to correct and the problem goes away - you are just left with the problem of correcting for wind-induced drift yourself and, of course, dealing with the different flight characteristics of ATTI mode.

The best way to ensure that this doesn't happen is to check that the aircraft orientation arrow on the map at takeoff is pointing in the same direction as the actual aircraft orientation. In this case the arrow will have been pointing around 30° south of the actual orientation, which was around NE.

Thanks for the very detailed and thorough explanation about what happened. I learned something new from your post.

 

[MarkG_007]

The best way to ensure that this doesn't happen is to check that the aircraft orientation arrow on the map at takeoff is pointing in the same direction as the actual aircraft orientation. In this case the arrow will have been pointing around 30° south of the actual orientation, which was around NE.

That is a very informative summary. And great tip about the orientation arrow. Tks

 

[Robert Weaver]

At 2:02 you can see a bird relatively close and appears to be flying away.

 

[GadgetGuy]

That is a very informative summary. And great tip about the orientation arrow. Tks

That is also completely consistent with my take aways, after a resulting crash from such a mismatch of compass orientation displayed in the app, just before takeoff.