Where is the "retrace original flight route" that DJI speaks of?

[Bigbells]

We were hijacking somebody's thread with a spirited discussion of Return To Home in regard to the P4P.

Hopefully the people in that discussion will see this post.

So where is this feature? I have experienced at least 10 RTH events since getting my P4P, but none where the bird retraced its flight path... instead, after rising to my pre-set RTH altitude if necessary, the aircraft returns the efficient way, in a straight line.

Several people have said that retrace is activated only when the RC is turned off. I haven't tried it (I only did it once, with a P2V, and that quad was never found.) But still, I'm not buying what some are saying. How would the aircraft know the difference between a) the RC being turned off and b) losing the signal from the RC? More importantly, what possible reason could there be that it should change the way the aircraft Returned To Home?

If someone shows me a video where they take a meandering flight and then the P4P Returns To Home using the same labyrinth of twists and turns that it took on the way out, I'll eat my hat.

 

[smiller]

If someone shows me a video where they take a meandering flight and then the P4P Returns To Home using the same labyrinth of twists and turns that it took on the way out, I'll eat my hat.

I don't think the feature was ever intended to do quite that, rather 'back out' of a situation a short distance in an attempt to regain signal. While much speculation abounds about how this is supposed to work, so far I'm not aware of anyone who has come up with any official answer or documentation. Apparently the only way we're going to find out how this feature works (or even if this feature works) is by careful experimentation on our own.

 

[Glenn Goodlett]

Here is my post copied from RC Groups on the subject;

I have been testing this and can conform that mine does not behave in this manner. It has never retraced its' path back to where it lost signal. I fly out to almost the limit of range then fly in a 45 degree angle away from myself until the craft looses connection. The craft has been out of touch for as long as 30 seconds but the path always shows the return as directly back to home. It never retraces any of the 45 degree line as far as I can tell from the logs.

Maybe my logs don't show what the craft was doing when disconnected, but, it never regains connection along the same path it got to that point on. I guess I can't complain it has always retuned without incident.

I was basically told that I was mistaken and the logs do not include what the craft does while it is disconnected. Problem is that doesn't make sense. It could be that I am wrong too.
At any rate, I think my testing may end since I feel like I'm going to have a stroke flying out of range purposefully at such a long distance, repeatedly. Also, I don't think I could ever bring myself to turn the transmitter off during flight.

 

[Bigbells]

rather 'back out' of a situation a short distance in an attempt to regain signal.

Zackly right, smiller. Here's video documentation from a flight this afternoon. I definitely should have uploaded it at higher resolution, but it's still possible to see how the P4P does a 180 and turns back along the flight path for maybe 50-100 feet before turning towards home.

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[Doctorcobani]

Check this vídeo, activate CC in YouTube before playing to see translation:

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In these video the P4P make intelligent RTH, back in the same route and not in straight line. The operator has covered the antennas to loss signal.

But I would like to know better how and when work in that way...

Enviado desde mi Nexus 6P mediante Tapatalk

 

[John Locke]

Several people have said that retrace is activated only when the RC is turned off. I haven't tried it (I only did it once, with a P2V, and that quad was never found.) But still, I'm not buying what some are saying. How would the aircraft know the difference between a) the RC being turned off and b) losing the signal from the RC?

It wouldn't, that's the point. The goal is testing signal loss, versus an initiated RTH with the RTH BUTTON. You can turn off the RC with the craft nearby to simulate losing signal, and you can watch the craft backtrack.

In addition to turning off the RC to experiment with this feature, you could also stand behind a brick wall, blocking the LOS of the RC with the craft, just a few hundred feet away while you watch the craft's behavior, saving the wait to view video from the bird. Just watch the signal strength bars at the top of the GO app to determine the integrity of the connection. Then when you want to reconnect, step out into the open to regain LOS again between radio and craft.

More importantly, what possible reason could there be that it should change the way the aircraft Returned To Home?

The reason behind the backtrack idea is for when you accidentally wander behind a mountain or building, and lose all connection, the craft simply backs up to where it was before to regain signal and give you a second chance at navigating correctly. For an INTENTIONAL RTH, initiated by the pilot, this is a lucid decision to come straight home at the prescribed RTH altitude, which is no accident. That's likely the theory behind the two different behaviors of Smart RTH versus a simply beeline RTH.

 

[smiller]

I was basically told that I was mistaken and the logs do not include what the craft does while it is disconnected.

There are two sets of logs, the .TXT files that are stored by DJI GO on the controlling device and the more detailed .DAT files stored on the aircraft. Of course the .TXT logs do not contain telemetry from when the aircraft was disconnected since there is no link, but the onboard .DAT logs will always contain the entire flight (assuming you can recover the aircraft of course.) The .DAT files can be downloaded from the aircraft via USB using the DJI Assistant PC application, although I'm not sure if anyone besides DJI can decode them completely.

 

[smiller]

The reason behind the backtrack idea is for when you accidentally wander behind a mountain or building, and lose all connection, the craft simply backs up to where it was before to regain signal and give you a second chance at navigating correctly. For an INTENTIONAL RTH, initiated by the pilot, this is a lucid decision to come straight home at the prescribed RTH altitude, which is no accident. That's likely the theory behind the two different behaviors of Smart RTH versus a simply beeline RTH.

Yes, I think this is correct and the distinction between the two is what is confusing people.

 

[F3honda4me]

I can confirm mine backs up when signal is lost. I flew out today and around a hill, and lost signal. Watching the video it turned around and traced its path a bit. When I regained signal i was able to stop any further RTH. The craft had maintained altitude instead of going to RTH altitude and did not turn toward home but instead toward the direction it had come from.

 

[Bigbells]

I can confirm mine backs up when signal is lost. I flew out today and around a hill, and lost signal. Watching the video it turned around and traced its path a bit. When I regained signal i was able to stop any further RTH. The craft had maintained altitude instead of going to RTH altitude and did not turn toward home but instead toward the direction it had come from.

If the aircraft is already above your RTH altitude, the aircraft stays at its current altitude for RTH. When the aircraft is below your RTH altitude, it rises to that altitude.

 

[John Locke]

Check this vídeo, activate CC in YouTube before playing to see translation:

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In these video the P4P make intelligent RTH, back in the same route and not in straight line. The operator has covered the antennas to loss signal.

But I would like to know better how and when work in that way...

Enviado desde mi Nexus 6P mediante Tapatalk

Looks to me like he intentionally flew behind that building tower to lose signal. However, this was definitely a planned demo with the overhead drone capturing the backtracking of the RTH. Nice video, thanks for sharing.

 

[smiller]

If the aircraft is already above your RTH altitude, the aircraft stays at its current altitude for RTH. When the aircraft is below your RTH altitude, it rises to that altitude.

But I think during the time that the unit is in backtrack mode the altitude will match the backtrack action, not rise to the RTH preset. Only after the unit determines that it cannot get signal back via backtrack will it go into full beeline RTH at the altitude preset.

Thanks to all doing and reporting the testing, this is the only way we're going to get answers.

 

[John Locke]

If the aircraft is already above your RTH altitude, the aircraft stays at its current altitude for RTH. When the aircraft is below your RTH altitude, it rises to that altitude.

Are you sure about that? It would seem more logical that the craft intentionally MAINTAINS it's backtrack altitude(s), otherwise it could hit something if it rises before backtracking.

 

[F3honda4me]

If the aircraft is already above your RTH altitude, the aircraft stays at its current altitude for RTH. When the aircraft is below your RTH altitude, it rises to that altitude.

I'm aware of that. But it will NOT do that while doing the backtrack. My RTH altitude is 300 feet. The craft stayed at the 100 feet I had it at when tx signal was lost.

 

[Bigbells]

Are you sure about that? It would make more sense to me that the craft initentionally MAINTAINS it's backtrack altitude(s), otherwise it could hit something if it rises before backtracking.

I was thinking that maybe the original poster was already above his RTH and was expecting the aircraft to drop down to it. He did say that RTH was actually initiated, and I took that to mean that the aircraft had already begun the straight-line RTH.

 

[John Locke]

I was thinking that maybe the original poster was already above his RTH and was expecting the aircraft to drop down to it. He did say that RTH was actually initiated, and I took that to mean that the aircraft had already begun the straight-line RTH.

It appears to me that signal loss was caused from him going behind a hill. That's why it backtracked at the original route elevations. If it had been initiated, then it would have made a beeline RTH, at the prescribed elevation, or higher if the craft was higher at the time.

 

[F3honda4me]

According to a DJI rep the craft will backtrack up to 60 seconds before initiating failsafe RTH if it still doesn't reconnect to the TX. Now that we know how backtrack works it's pretty dang cool lol.

 

[smiller]

According to a DJI rep the craft will backtrack up to 60 seconds before initiating failsafe RTH if it still doesn't reconnect to the TX. Now that we know how backtrack works it's pretty dang cool lol.

Yep. My home location is in a clearing among tall trees and if I lose signal (probably likely sooner or later) the backtrack feature would be very welcome, rather than a full panic RTH. It's one of the reasons I selected the P4P so I hope it works as well as some of the initial tests indicate.

 

[Bigbells]

According to a DJI rep the craft will backtrack up to 60 seconds before initiating failsafe RTH if it still doesn't reconnect to the TX. Now that we know how backtrack works it's pretty dang cool lol.

"Up to 60 seconds" sounds like somebody might have been giving their best guess. Mine backed up for less than 25 seconds, which included the time to do the 180. But, if the time is variable, I wonder what factors cause it to vary.

I was going to keep pushing forward until RTH was forced, because I didn't have to get much further away before I started getting closer. (I was trying to go around the block... big blocks out in the country.)

 

[smiller]

But, if the time is variable, I wonder what factors cause it to vary.

Well I would think one big factor is how long it takes to reaquire what the system thinks is a reliable link between controller and aircraft. I guess the way to test this would be to fly a parallel or zig-zag path and then turn off the controller and see how long the backtrack is followed until full RTH mode tales over.