Flying Under a Bridge

I did, but not for a full 3 seconds, and by then, I was on the far side, out from under it. At 35 mph, 51 feet per second, you can cover a lot of ground in a very short period of time! As Adm. David Farragut said, "D*mn the torpedoes, full speed ahead!" :D
It's not like you couldn't afford to lose a drone, right? How many is in your fleet? Isn't it 6 now?
 
It's not like you couldn't afford to lose a drone, right? How many is in your fleet? Isn't it 6 now?
At the time, it was one of only three P3P's, but now it has four younger siblings, two P4’s and two P4P's, so 7 in total. Got to have a few sacrificial lambs to experiment with! Some the earlier birds are easier to put at risk, and better suited for these types of flying, with no OA and full manual control over all features! I have plans to fly under the full length of a 1000 foot long pier, and one of the P3P's will be the guinea pig!
 
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At the time, it was one of only three P3P's, but now it has four younger siblings, two P4’s and two P4P's, so 7 in total. Got to have a few sacrificial lambs to experiment with! Some the earlier birds are easier to put at risk, and better suited for these types of flying, with no OA and full manual control over all features! I have plans to fly under the full length of a 1000 foot long pier, and one of the P3P's will be the guinea pig!
I'd like to witness that one. ATTI zone ahead. Hope it's not windy. Maybe not, you might be able to keep GPS locked in with enough satellites. Nice mission plan.
 
Atti mode?
I did, but not for a full 3 seconds, and by then, I was on the far side, out from under it. At 35 mph, 51 feet per second, you can cover a lot of ground in a very short period of time! As Adm. David Farragut said, "D*mn the torpedoes, full speed ahead!" :D
 
Atti mode?
Nope. Plain old P-GPS. Found the video. Here it is!

Sunset Flying Under 5 Lane Bridge with P3P on Sunday, April 17, 2016 (26 secs)
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Here's the topside view of the bridge, which has 5 traffic lanes and two bike lanes.
IMG_6130.JPG
 
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I was attacked by birds while flying under a bridge on one of the rivers in Georgia. I was able to out run them but it gave me a pretty good scare
 
just keep in mind that concrete bridges have more steel rebar than probably concrete. In other words, inside of that concrete is a boatload of steel.
 
I was attacked by birds while flying under a bridge on one of the rivers in Georgia. I was able to out run them but it gave me a pretty good scare
Birds roost under bridges, and will aggressively defend their nests, so, one more reason to fly fast, once everything is properly lined up! :cool:
 
For anyone contemplating a flight under a bridge without VLOS, don't forget there is almost a 1/4 second (typically 200ms) lag in your display, versus reality. You have to line yourself up really good because your reactions to correct any drift could be too slow to compensate in tight quarters. That's the downside to digital video communications. Consider, the video image compression at the camera > transmission to ground > receiving the signal by the RC > decompression of video packets by Go4 app > then displaying the video to the tablet. All this takes some time, about 180-220 milliseconds, which is amazing to me. The benefit of digital transmission is the range capability, along with video clarity on the display, virtually no snow (when in range). The distance doesn't affect this timing hardly at all, it's the compression and decompression that creates this lag.

DJI knows this lag needs to improve, and I believe they will continue to improve Lightbridge in the future. I believe this has improved with Lightbridge 2 (which is used in their high end drones), they claim 50ms, but I don't believe it. I read that Mavic's Ocu-Sync has reduced transmission lag also, but I haven't measured to confirm the numbers yet. I assume P5 will be upgraded to Ocu-Sync to be compatible wirelessly with the DJI goggles, and have less lag.

This is different than race quads that use analog video communications, which have no compression or decompression steps for transmission, hence the lag is only a few milliseconds. You virtually get real time control of the drone through the goggles, which is essential when navigating a drone at speeds of 80mph. The downside is less resolution, snow in the video feed, and less range capability.
 
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For anyone contemplating a flight under a bridge without VLOS, don't forget there is almost a 1/4 second (typically 200ms) lag in your display, versus reality. You have to line yourself up really good because your reactions to correct any drift could be too slow to compensate in tight quarters. That's the downside to digital video communications. Consider, the video image compression at the camera > transmission to ground > receiving the signal by the RC > decompression of video packets by Go4 app > then displaying the video to the tablet. All this takes some time, about 180-220 milliseconds, which is amazing to me. The benefit of digital transmission is the range capability, along with video clarity on the display, virtually no snow (when in range). The distance doesn't affect this timing hardly at all, it's the compression and decompression that creates this lag.

DJI knows this lag needs to improve, and I believe they will continue to improve Lightbridge in the future. I believe this has improved with Lightbridge 2 (which is used in their high end drones), they claim 50ms, but I don't believe it. I read that Mavic's Ocu-Sync has reduced transmission lag also, but I haven't measured to confirm the numbers yet. I assume P5 will be upgraded to Ocu-Sync to be compatible wirelessly with the DJI goggles, and have less lag.

This is different than race quads that use analog video communications, which have no compression or decompression steps for transmission, hence the lag is only a few milliseconds. You virtually get real time control of the drone through the goggles, which is essential when navigating a drone at speeds of 80mph. The downside is less resolution, snow in the video feed, and less range capability.
Don't try this at home, unless you know what you are doing! :rolleyes:
 
You could set up a mission. It will have everything it needs on board
Depends. You can't use a GO 4 mission with waypoints, unless you can first fly the mission manually without waypoints, and it also won't allow setting waypoints more than 1000m away, as I recall. You need to have a Lost Control Mision Continues (LCMC) capability, which used to be no problem with other apps. However, lately, that capability is severely crippled by the current Developer SDK. I know it was an issue for Litchi. Instead of continuing the mission, it would just hover in place until the battery died, and then land. Not good, under a bridge, into saltwater! :eek: How would you go about it?
 
Even with los my experience with litchi is it will finish the flight from way point to way point. I could be vastly over simplifying this you guys here usually have very good suggestions. No reason to doubt you now. Please keep up the good work for all of us to learn from
 
Even with los my experience with litchi is it will finish the flight from way point to way point. I could be vastly over simplifying this you guys here usually have very good suggestions. No reason to doubt you now. Please keep up the good work for all of us to learn from
Even Litchi still needs GPS to continue its mission in a LCMC situation, so one would need to run a couple of test flights to see how it reacts in a safer environment, that would simulate an under bridge, over water flight, where loss of both signal and loss of GPS could occur, without the water, and close enough to recover signal, as needed! 2 miles away certainly won't work! ;)
 
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I thought RTH altitude depended on a GPS signal. How would the drone determine the correct altitude under a bridge? I thought with loss of GPS it simply hovers until acquisition.

Loss of GPS is different that loss of signal.

When my drone has had loss of GPS, it will fly under manual but will hover until I take over.

Hovering in GPS mode is very different from hovering in ATTi mode. In the second case wind drift can be significant. Another reason to avoid flying in windy conditions when you have any expectation of being forced into ATTi mode.
 
On the P4P, VPS is available up to 10m above the surface, and works over water, as well. Best over still water. 10 feet over the water is a safe height, as long as fish aren't jumping (which has happened to me) and no one is fishing over the edge of the bridge! Loss of GPS puts you into ATTI with VPS if under 10m. The key is making sure you don't lose control signal for more than 3 seconds while still under the bridge. Fly fast enough that you are out from underneath the bridge when that loss of signal kicks in, so that RTH will safely restore signal through elevation. YMMV. ;)
 
Sorry for the delay I thought I posted a reply last night Anyway will try again. It has been my experience with a P3A and litchi even with LOS it flight just continues from way point to way point because all of the flight instructions are already there. Mabel I am vastly simplify the issue. Everybody knows you guys out have always been able to come up with the right way to get to the bottom of this issue. There certainly is no reason to doubt GadgetGuy. He has provided a great deal of help to everyone here on the forum. I have 0% phantom 4 time.
 
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Sorry for the delay I thought I posted a reply last night Anyway will try again. It has been my experience with a P3A and litchi even with LOS it flight just continues from way point to way point because all of the flight instructions are already there. Mabel I am vastly simplify the issue. Everybody knows you guys out have always been able to come up with the right way to get to the bottom of this issue. There certainly is no reason to doubt GadgetGuy. He has provided a great deal of help to everyone here on the forum. I have 0% phantom 4 time.
There are two different variables involved when flying under a bridge. The most important is signal control. The second is GPS signal. However, even a Lost Control Mission Continues capability (assuming no newer SDK limitations, which have been an issue with more recent aircraft) requires GPS to follow the flight instructions preprogrammed as part of the mission. If GPS is lost under the bridge, which is highly likely, if control is also lost because one is flying at an angle from above the bridge (like 2 miles away in my crazy flight above in April of 2016), the mission cannot continue to the next waypoint because GPS has also been lost. Various combinations of signal control and GPS status are possible in other scenarios, where a Lost Signal Mission Continues would work, but they would still require GPS, which is possible while flying under some bridges, even when control signal is lost, but just not with a concrete bridge that is over 70 feet wide, only 30 feet above water. You have to fly fast, before the aircraft "realizes" that it has no RC control and no GPS, to make it out the far side and recover both GPS and signal! Good luck, and be careful! Post both the successes and the failures here! :D
 

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