Flying under a bridge but only 4 metres away - thoughts?

[Buel]

Hi all.
A good friend of mine got some great shots with his DJI Flip while flying under a train track bridge - he was within 4 meteres of the drone at all times. However, could this still have affected the signal? I have tried something similar and I experienced signal issues with my Mini 4 Pro but can't understand why? Really don't want to try to rise up with an automated RTH with a bridge above you?

 

[mavic3usa]

Set your RTH setting upon lost connection to Hover.

 

[GadgetGuy]

Set your RTH setting upon lost connection to Hover.

Actually, it is the Lost Signal behavior that needs to be set to hover if signal is lost under an obstruction.

Also, fly faster. It takes at least 3-5 seconds after signal loss for the Lost Signal setting to take effect. If you are already past the signal obstruction by then, the Lost Signal setting won't ever have a chance to kick in, or if it does, you will have already cleared the overhanging obstruction by then, where it can still safely ascend, if set to ascend first to a predetermined height, so hovering isn't necessary.

I once flew under a 5 lane concrete bridge over salt water with the Phantom 3 Pro from several miles away by flying full speed at 33 mph. Drone was on the other side before signal would have been lost from either the RC or GPS. Auto exposure didn’t work out so well on the video, though, as it grossly overexposed coming out from under the dark bridge, into full sunlight, as it made it through. Otherwise, it was a cool shot! Hovering would not have been an option under the bridge from several miles away. Ah, the good old days of the Wild West of drone flying! LOL!

 

[mavic3usa]

Actually, it is the Lost Signal behavior that needs to be set to hover if signal is lost under an obstruction.

Also, fly faster. It takes at least 3-5 seconds after signal loss for the Lost Signal setting to take effect. If you are already past the signal obstruction by then, the Lost Signal setting won't ever have a chance to kick in, or if it does, you will have already cleared the overhanging obstruction by then, where it can still safely ascend, if set to ascend first to a predetermined height, so hovering isn't necessary.

I once flew under a 5 lane concrete bridge over salt water with the Phantom 3 Pro from several miles away by flying full speed at 33 mph. Drone was on the other side before signal would have been lost from either the RC or GPS. Auto exposure didn’t work out so well on the video, though, as it grossly overexposed coming out from under the dark bridge, into full sunlight, as it made it through. Otherwise, it was a cool shot! Hovering would not have been an option under the bridge from several miles away. Ah, the good old days of the Wild West of drone flying! LOL!

Yeah that's what I meant, when you lose the connection, set it Hover rather than RTH so the drone doesn't rise; at least the older one with smart RTH or top sensors. I was thinking FPV world where the instant you lose the signal, the drone will freeze and the idea is the quicker the better which means it usually (not always) takes just several steps towards to regain the signal (about the same distance when you had a connection just a few seconds ago before you lost it). I guess the latest FPV drones will actually back out of that tunnel if you lose the signal inside so backing out in an attempt to regain the connection but I haven't tried it, I'm not up for that at the moment.

Honestly I guess I don't know why a drone would need to RTH right away on lost signal since it will do that anyway when the battery gets low enough, right? Hover for 2-3 minutes or 10 minutes or whatever and then RTH but yeah few miles out is risky. Is there a setting for low battery RTH?

 

[GadgetGuy]

Yeah that's what I meant, when you lose the connection, set it Hover rather than RTH so the drone doesn't rise; at least the older one with smart RTH or top sensors. I was thinking FPV world where the instant you lose the signal, the drone will freeze and the idea is the quicker the better which means it usually (not always) takes just several steps towards to regain the signal (about the same distance when you had a connection just a few seconds ago before you lost it). I guess the latest FPV drones will actually back out of that tunnel if you lose the signal inside so backing out in an attempt to regain the connection but I haven't tried it, I'm not up for that at the moment.

Honestly I guess I don't know why a drone would need to RTH right away on lost signal since it will do that anyway when the battery gets low enough, right? Hover for 2-3 minutes or 10 minutes or whatever and then RTH but yeah few miles out is risky. Is there a setting for low battery RTH?

Yes, DJI has made various changes to Lost Signal behavior to attempt to restore the signal by first flying back along the route just flown, for a certain distance or time, before the set RTH behavior. Unless you are flying VLOS, hovering from a long distance away generally means it will eventually land in place if you cannot restore signal by physically getting to the drone in time. Not good while flying under bridges over salt water from several miles away.

The main reason for signal loss in open skies is flying behind an intervening tall tree, building, or hill, where setting a RTH as high as possible will quickly restore signal, unless you are at the extreme edge of signal strength despite clear LOS, where elevating will actually increase the distance away, exacerbating the problem, and making it unlikely to have enough battery to return home, because of wasted battery elevating, and then needing to eventually descend, especially under a forced landing that you cannot prevent, unless you can regain control. Always adjust your loss of signal and RTH settings for the best outcome for each specific flight.

I am also not willing to test the current behavior when loss of signal is set to hover to see whether the low battery RTH will override it. Not sure. Low battery RTH percentage is now no longer under user control, and does require signal to cancel the low battery RTH when that percentage is reached, or the calculated return distance requires immediate RTH.

Lots of factors to consider when pushing the limits.

 

[mavic3usa]

I am also not willing to test the current behavior when loss of signal is set to hover to see whether the low battery RTH will override it. Not sure. Low battery RTH percentage is now no longer under user control, and does require signal to cancel the low battery RTH when that percentage is reached, or the calculated return distance requires immediate RTH.

This is what I found when testing Avata since the FPV drone world is where I get closer to the end of the battery and maybe in a tunnel or under a bridge to close a connection; would never do this with a drone like Mavic 3 Pro.

M

Post in thread 'Flew my drone into the woods'

May 13, 2025

Here's what I discover for the Avata FPV and it's ideal but it's not the end of the world.

Using the Goggles and the MC/RC, you can simulate a "disconnect" or "loss of signal" by powering off the MC. At that point, you can still see everything going on thru the Goggles and this is what I found:

The setting says something like "action upon signal disconnect" and therefore that means no relationship to the battery. You may choose between RTH, HOVER, or Land.

In short, when the setting is HOVER, I sent the drone out quite a distance and I shut off the MC and the drone stopped and...

• mavic3usa

• 

 

[GadgetGuy]

This is what I found when testing Avata since the FPV drone world is where I get closer to the end of the battery and maybe in a tunnel or under a bridge to close a connection; would never do this with a drone like Mavic 3 Pro.

M

Post in thread 'Flew my drone into the woods'

May 13, 2025

Here's what I discover for the Avata FPV and it's ideal but it's not the end of the world.

Using the Goggles and the MC/RC, you can simulate a "disconnect" or "loss of signal" by powering off the MC. At that point, you can still see everything going on thru the Goggles and this is what I found:

The setting says something like "action upon signal disconnect" and therefore that means no relationship to the battery. You may choose between RTH, HOVER, or Land.

In short, when the setting is HOVER, I sent the drone out quite a distance and I shut off the MC and the drone stopped and...

• mavic3usa

• 

Since I always cancel low battery RTH, I haven’t paid close enough attention to know whether it is always at a fixed percentage, or whether it is algorithm based, depending upon how far you are away from home point. Do you happen to know? If the latter, can it be triggered multiplied times during a flight after canceling it once? Certainly, a dynamic home point (Mavic 4 Pro with RC Pro 2) and staying close enough to the drone should alleviate issues posed by lost signal settings being overridden by low battery RTH ascension, by eliminating the possibility of an ascension where it lands in place instead. Is that 50 feet?