Hey, there. Been investigating the use of my Phantom 3 Pro for basic railroad bridge inspection. I work for a railroad, so don't worry about safety (at least rail-related safety) for the purposes of this discussion.

For the most part, I've had success, however occasionally, I've run into environmental conditions that have made performing the survey all but impossible. Unfortunately, a lot of the most "drone friendly" bridges are in these kinds of locations; remote, elevated, heavily forested, etc...
Here's what happens. It's winter here, so there's snow and ice on and around the rails.  No surprise, however, tracks are often elevated, and the rock on the sides of elevated tracks frequently slopes down pretty aggressively. Add snow and ice to this, and you run into a slippery and often dangerous situation. In addition, rail bridges are often in wooded areas, so on either side of the rails are canopies of trees, frequently only providing overhead clearance enough for a train to pass through - somewhere around 10' wide. This canopy also often reduces or eliminates GPS coverage.

Because of the sloping rocks and the fact that trees grow right up to the edge of the track, I end up having to launch from the middle of the rail (again, I work for a railroad), but this means I can almost never calibrate my compass.

So, here's my question: With no compass, no GPS, and restricted vertical clearance (even if I launch without compass calibration and in ATTI mode), do any of you think the Phantom 3 is up to the task?

How reliable and honestly, controllable, is the Phantom 3 without a compass or GPS?

Thanks in advance for your thoughts.

Don't worry about the compass, calibrate it once at an awesome location and leave it till the app ask for a new calibration.I flew from one of these ships and had no problems.


Nite that it was a Phantom 2 but the difference should be minimal I think.

Balthazar, thanks. I actually tried that, but when I tried to turn on the motors after moving, I got a compass error pop-up in the app and it wouldn't allow me to turn them on. Had never seen this before.

You could put just a little distance between the phantom and the track by say laying the phantom backpack on the ground and then setting the phantom on top of it for take-off.  Actually flying in your environment in ATTI mode will be quite difficult especially if its windy.

If the places are that closed in, they shouldn't have to much wind. Without wind it should be fairly  easy to fly without GPS>

Thanks for the ideas. I tried to launch off my backpack, and that was OK. There was little protection from the trees since they're devoid of leaves.

Actually the app wouldn't even allow me to energize the motors due to the compass error.

"So, here's my question: With no compass, no GPS, and restricted vertical clearance (even if I launch without compass calibration and in ATTI mode), do any of you think the Phantom 3 is up to the task?

How reliable and honestly, controllable, is the Phantom 3 without a compass or GPS? "

You can turn GPS off but you can't  fly without compass, it's always on and is necessary for safe, controllable flight.
To answer your question, go to a large, open area and fly ... switch to atti mode and you are now flying without the benefit of GPS.
That should give you an idea of how controllable the Phantom is in an area with poor GPS.
Of course this will vary with wind as your Phantom will not have position holding without GPS.
It will have altitude holding.
I suspect you'll probably have GPS much of the time anyway but you may get some situations where you are restricted by reduced view of the sky.

You have two potential compass issues.
Flying very close to a large steel bridge, your compass will be affected by the magnetic field of the steel and the Phantom might start to spiral around.
The distance will vary with the amount of steel but you might be good up to 10 feet  away?
You can slowly approach, watching for signs of wandering.

Taking off from near steel is another issue.
Never calibrate the  compass in an area affected by proximity to steel  objects.
You need your Phantom to be calibrated for  the earth's normal magnetic field .. not the distorted field near a big lump of steel.
You can reduce the compass error issue by getting your Phantom further away from the rails.
Either off to the side somewhere or perhaps by having an assistant hold the Phantom up above their head for hand launching above the magnetic field generated by the rails etc.

Good on ya, mate. Thanks, labroides.

I'm going to go back to this particular location again next week, and will try to launch from a road bridge that's parallel and located a couple hundred feet away. Was having trouble getting a GPS signal there yesterday, and the bridge shoulders were snow covered, so I didn't feel comfortable. The mapping app I use won't launch without GPS.

I agree with labroides .  Flying near steel is always problematic.  Just about every crash I have had is because I flew too close to steel; it causes havoc with the compass and it acts like a magnet!  No matter how fast I reacted or whether in atti or GPS modes it is like a boat getting sucked down a drain hole.  The magnetic fields and eddies generated around railway tracks and bridges would be enormous.  Good luck, give it a try but I'm not optimistic for you.

Endo, thanks. I agree, but that's what makes it fun, right?

dmwierz Posted at 2016-1-22 14:00
Endo, thanks. I agree, but that's what makes it fun, right?

You have powerful steel in USA!
No drones lost to steel here and I've never been shy of the stuff
Flying off a Steel Boat
(Posted to my Phantom Blog by a Brave Fisherman)