Greetings Phantom Flyers,

I was recently shooting suspended stage equipment from the 45th floor (rooftop) if a condo building.

I always feel weird about not taking off from the ground but I was worried I wouldn't be able to see the drone well enough from ground level to the 45th floor so I attempted launching from the roof.

  Immediately after launch I experienced a flyaway. The unit was non-responsive on the controls but thankfully it headed straight for me as opposed to over the edge of the building and I was able to grab it and kill the engine.

  I didn't want to attempt to trouble shoot it on the roof so I took it back down to
ground level and everything was fine, and after a few more operations recently I can safely say it was a unique event.

  I guess my question would be: do I need to do something special to configs to take off from heights?! ie. Does the unit consider elevation for RTH point? In essence did my P4 think it was taking off from 0 or 450ft???

Never take off on a rooftop or balcony. You just asking for trouble.

It should treat the rooftop as 0 elevation. Was it a metal roof? This can cause compass errors. Would there be RF interference such as transmitters such as cell phone towers on the roof? Elevation should not be an issue. It's likely another cause. Possibly magnetic interference from HVAC or elevator motors?

Capo Posted at 2017-6-7 08:17
It should treat the rooftop as 0 elevation. Was it a metal roof? This can cause compass errors. Would there be RF interference such as transmitters such as cell phone towers on the roof? Elevation should not be an issue. It's likely another cause. Possibly magnetic interference from HVAC or elevator motors?

I actually had great connectivity, full signal, and everything checked out before I gave it throttle. As soon as it was airborne it headed due North.

Very true though, that there could be a whole whack of things on a condo rooftop transmitting or receiving. Concrete form construction though, so no metal for the most part.

Good to know that the RTH point always assumes elevation is 0.

Maxi3D Posted at 2017-6-7 07:56
Never take off on a rooftop or balcony. You just asking for trouble.

I agree, it definitely doesn't feel right to take off from a roof.

I'd just like to understand why it's so problematic.

One thing for sure though. On top of a condo, there's going to be a ton of 2.4 GHz interference from Wi-Fi, phones, and microwave ovens.

fans33885c62 Posted at 2017-6-7 09:21
I actually had great connectivity, full signal, and everything checked out before I gave it throttle. As soon as it was airborne it headed due North.

Very true though, that there could be a whole whack of things on a condo rooftop transmitting or receiving. Concrete form construction though, so no metal for the most part.

If the rooftop is concrete, then you can bet there's a LOT of metal in it

As a retired general contractor who built high rise buildings you have no idea how much steel is in the roof deck approximately 3 inches below the surface. Here is  sample picture of the steel grid work in those floors and roofs-

racer888 Posted at 2017-6-7 10:16
As a retired general contractor who built high rise buildings you have no idea how much steel is in the roof deck approximately 3 inches below the surface. Here is  sample picture of the steel grid work in those floors and roofs-

Yep, if only people knew. I'm amazed it lifted off the roof.

Maxi3D Posted at 2017-6-7 07:56
Never take off on a rooftop or balcony. You just asking for trouble.

I second this

definetly magnetic compass problem. i tested that before. roofs are full of metal. sometimes you can take off without problem and then you get rapid magnetic field change which caused your flyaway.

if you really have no other choice but starting of a roof you use a big wooden or plastic box to get some space between ground of rood and your drone.

but of course i will agree with all others before: dont you do it buddy! not worth the problems

There is no problem at all flying from a reinforced concrete roof, just leave the aircraft down on the ground (well away from any concrete) while you go up there and then fly it up, and then land it back on the ground again before you return down to collect it.  (Remember that your radio signal will not go through reinforced concrete)

What you experienced is exactly what happens when you take off within a local magnetic field.  You can use a compass, eg the one on your phone/tablet to check that the magnetic field at the launch position is close to the earths magnetic field.  If it is significantly different or varies as you move around then you are going to have problems.  You do need to check the magnetic field tilt as well as direction for a proper check.

If you do have problems after take off then switching to atti mode may help, depending on if the problem is direction or tilt.  

It is true that there is much magnetic interference from a roof structure. You may want to rethink over this point.

fans33885c62 Posted at 2017-6-7 09:21
I actually had great connectivity, full signal, and everything checked out before I gave it throttle. As soon as it was airborne it headed due North.

Very true though, that there could be a whole whack of things on a condo rooftop transmitting or receiving. Concrete form construction though, so no metal for the most part.

I would concur with Capo about this as well. Regarding the roof you were on though, I'm assuming it was on a completed building and not on one that still being renovated? The surrounding area in addition to the building itself would be very likely to have multiple WiFi signals, satellite dishes that could cause magnetic, electrical or magnetic interference. Just to clarify, did you get any sort of error messages when this happened?

If you were in GPS mode when this happened, try switching to ATTI mode to try and regain control in the future.

I agree with what has been said about reinforced concrete causing issues. What no one has asked and you did not say was, did you do a compass calibration on the roof before you flew?  (That would be a bad idea).

"do I need to do something special to configs to take off from heights?! ie. Does the unit consider elevation for RTH point? In essence did my P4 think it was taking off from 0 or 450ft???"

Height makes no difference to the Phantom.
All it knows is that the launch point = zero feet whether you launch from a moiuntain top of the edge of the sea.

The suggestions about wifi interference are irrelevant.
They simply make the signal patchy but never cause the Phantom to fly away.
Similarly switching to atti would have probably made no difference as the problem was to do with the compass, not GPS.
Your Phantom would have had a compass error and switched to atti by itself.

"concrete form construction though, so no metal for the most part."
As demonstrated above, this is a huge mistake.
Launching from steel or reinforced concrete (which is half steel) can cause big problems as has been proven many times.
If you want a technical explanation for what happened, read this post:  http://www.phantompilots.com/thr ... /page-2#post-915176

DJI-Mark Posted at 2017-6-7 11:11
It is true that there is much magnetic interference from a roof structure. You may want to rethink over this point.

Agreed Mark, I was sceptical about the rooftop takeoff, it just made sense at the time because we were shooting other video of an installation on the roof.

We took extra precaution during pre-flight checks, so she didn't get away from us but I know I'll get more calls for inspections like this in the near future so it will be good to have a solid explanation.

racer888 Posted at 2017-6-7 10:16
As a retired general contractor who built high rise buildings you have no idea how much steel is in the roof deck approximately 3 inches below the surface. Here is  sample picture of the steel grid work in those floors and roofs-

Good call Racer, I work in ICI and Commercial Con, we do inspections for a lot of builders in the Toronto area. That particular inspection was for Davit Arms that get installed at the top, I thought I could isolate the P4 enough from the roof to be able to operate, but nope.

We have a pretty extensive pre-flight checklist, so thankfully we prevented the fly away, but definitely a good learning experience.

The added preparation should be applauded. It helps to always think of your area and location and be mindful of what is around for you. At the same point, Jaime made a good point on flying in Atti mode. Practice makes perfect. Keep flying safely.

Speaking of magnetic interference from metal. I was in an open field with tall vegetation, tried to launch from the hood of my car, no go, magnetic interference error. Had to drive out of the field and launch in a clear area.

tomramos213 Posted at 2018-2-1 16:50
Speaking of magnetic interference from metal. I was in an open field with tall vegetation, tried to launch from the hood of my car, no go, magnetic interference error. Had to drive out of the field and launch in a clear area.

How about the metal hood of your car, that would cause major interference with the compass.

Aardvark Posted at 2018-2-1 17:17
How about the metal hood of your car, that would cause major interference with the compass.

Launching from the roof of the car might have been more successful, as you would reduce the effects of the probable magnetic fields of the alternator and starter motor?

OneTenthOfAMileHighClub Posted at 2018-2-1 18:45
Launching from the roof of the car might have been more successful, as you would reduce the effects of the probable magnetic fields of the alternator and starter motor?

Not in the least. The alternator does not produce any magnetic field unless the motor is running, and the starter motor is too far away to have any effect. But the metal roof is less than an inch from the compass unit, so it will have a serious adverse effect.

OneTenthOfAMileHighClub Posted at 2018-2-1 18:45
Launching from the roof of the car might have been more successful, as you would reduce the effects of the probable magnetic fields of the alternator and starter motor?

The roof of the car wouldn't be any better really.

A simple test can be done to check the effect on the compass' in the P4. With all connected and powered up, in DJI Go 4 go into the 'Main Controller Settings' / 'Advanced Settings' / 'Sensors' and tap on the 'compass' tab.

There you will see two bars giving a representation of the 'interference' detected by compass 1 (At bottom of front right leg, as you look at front of aircraft); and compass 2 (bottom of left leg).

Hold a steel spoon beside either compass 1 or 2 and see the effect it has on the readings, moving away a few inches and its effect will not be seen, but its a small area of metal.  Larger areas would have greater effect at greater distance.
You can also try this with different metals if you want. See what affect they have.

There are two compass' for redundancy, if one fails then the other is used, a yellow dot beside the compass name shows which is currently in use.

tomramos213 Posted at 2018-2-1 16:50
Speaking of magnetic interference from metal. I was in an open field with tall vegetation, tried to launch from the hood of my car, no go, magnetic interference error. Had to drive out of the field and launch in a clear area.

"I was in an open field with tall vegetation"

Were they Brussel Sprouts ? They're loaded with Iron (Sorry, I couldn't resist that).

This happened to me launching from a brige...Too much metal!!!

The steel rebar in rooftop and other building structural steel most likely caused severe compass errors - even if you did not receive any compass errors on the DJI GO 4 app.  The same thing can happen if you ever attempt to take off from a reinforced concrete roadway, driveway or parking lot.  

In the future you MAY be able to get around this issue on the rooftop by placing your P4P on top of an overturned plastic trash can and using that as a launch pad.  This will place the aircraft ~3 feet above the reinforced concrete surface.  But I would take off manually, and if the aircraft starts tilting in any direction either as it is lifting off or after rising a couple feet, immediately land and abort.  Another option is for you to stand on the roof but have the aircraft at ground level (on grass would be best) in a safe area away from pedestrians, takeoff and fly up to your location.  There should be no issue with landing on the roof after takeoff as compass errors tend to impact takeoff only.  Also, if you lose communication with the drone it will return safely to its takeoff location at ground level. Just be sure to set your RTH height ABOVE the max height of the building and any antennaes, etc. mounted on it.

I discovered long ago that DJI aircraft can experience compass errors and not hover stably if I attempt to takeoff from reinforced concrete of any type. BUT I have always been able to land on those surfaces without issue after taking off from nearby grassy or blacktop surfaces.  Also, be wary of of attempting to takeoff from a thin sod covering over underground concrete structures, rebar and structural steel in the underground structure can also cause compass errors and stability issues on takeoff.

I took a hard lesson today. Don't ever try to fly drone from rooftop. My quad just flown away uncontrollably as soon as it took off. I'm so lucky, that it didn't hit anyone, and it didn't broke, just some scratch on the body. I'm also glad that i haven't bought DJI yet. I've gotten cheap UAV for learning to fly, BUGS 5 W. Imagine if i drop a DJI UAV from 4th floor rooftop. I'm planning on buying one as soon i master how to fly properly.

I echo the concern others have had about concrete rooftops. I've noticed that any concrete surface, specifically more modern concrete surfaces do not allow very good compass orientation at all. It seems any concrete surface I've tried gives me a compass error message on my drone. There seems to be rebar in nearly any concrete surface these days. Simply moving the drone and re-booting the aircraft eliminates the error message. No calibration completed with the compass.

iamjustjohn Posted at 2018-9-21 12:41
I echo the concern others have had about concrete rooftops. I've noticed that any concrete surface, specifically more modern concrete surfaces do not allow very good compass orientation at all. It seems any concrete surface I've tried gives me a compass error message on my drone. There seems to be rebar in nearly any concrete surface these days. Simply moving the drone and re-booting the aircraft eliminates the error message. No calibration completed with the compass.

i did it worse ( i think ). i did it on, tin roof.

That's an interesting experience. When taking off from higher elevations, like rooftops, the drone can miscalculate its home point or altitude reference, which may explain the flyaway. Always reset the home point manually before launch to avoid confusion, and ensure GPS is stable. For accurate project planning especially at elevation tools like Construction Takeoff Services help factor in site specific conditions, saving you from surprises.
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