Failsafe RTH Behavior when flying below takeoff Height

[BobN2Tech]

I often takeoff my mini 2 on top of a 300-900 ft cliff and then I want to have it descend below the cliff to grab some footage of the cliff walls, so the altitude indicator will become negative. However, I am not sure what would happen if the signal is lost between the aircraft and RC because being blocked by the cliff and for more than 11 seconds issues a failsafe RTH. According to the manual it will first "fly backwards 50m on its original flight path, then ascend to the RTH setting". However, if the aircraft is less than 50m from the cliff edge, according to this description, it will smack right into the cliff. I would think a better way would be to have the aircraft ascend to its RTH first, then follow the straight line back. Has anyone experienced this situations?

 

[Meta4]

According to the manual it will first "fly backwards 50m on its original flight path, then ascend to the RTH setting". However, if the aircraft is less than 50m from the cliff edge, according to this description, it will smack right into the cliff.

If the drone managed to fly the last 50 metres without bumping into an obstacle, why would you think it would smack into the cliff when it reverses course and flies 50 metres back on the path it came in?

I would think a better way would be to have the aircraft ascend to its RTH first, then follow the straight line back. Has anyone experienced this situations?

The reason DJI refined the failsafe RTH to backtrack, was because just backtracking 10 metres is probably all that's required to reconnect.

 

[Gagey52]

Firstly welcome to the forum from the land of Oz. I was under the impression that the RTH if set above the home point, that’s the height it would ascend to before coming home even from a negative height.

 

[BobN2Tech]

If the aircraft at the moment of disconnect is below the cliff takeoff point and the home point is on top of the cliff behind the aircraft, but not visible because the aircraft is currently below, and say only10M from the cliff wall, a straight return on its flight path without ascending first above the cliff's top edge would smack into the cliff. If indeed the description in the manual is incorrect, and it in fact first ascends to the RTH home altitude, it would not be a problem. But I would hate to find out that's not the case.

 

[Meta4]

Firstly welcome to the forum from the land of Oz. I was under the impression that the RTH if set above the home point, that’s the height it would ascend to before coming home even from a negative height.

Originally DJI drones would simply rise to RTH height and gome come, but more recent models with obstacle avoidance and faster processors have a more advanced procedure for Failsafe RTH by backtracking and if signal isn't reconnected, then going to the original RTH method.

 

[BobN2Tech]

I certainly understand that reason to attempt reconnection by backtracking, but under certain flying conditions, like I was doing, or flying over a mountain top (or even a building) and if you descend a bit on the other side and it loses connection, less than 50m from the other side of the obstacle, it would be nice to have an option to skip the initial backtrack or set a smaller value under these circumstances. I realize this now, and one must be careful when doing this type of flying so that the aircraft must be always be at least 50M from the obstacle if on the flight path home.

 

[Meta4]

I certainly understand that reason to attempt reconnection by backtracking, but under certain flying conditions, like I was doing, or flying over a mountain top and if you descend a bit on the other side and it loses connection, less than 50m from the other side of the obstacle, it would be nice to have an option to skip the initial backtrack or set a smaller value under these circumstances. I realize this now, and one must be careful when doing this type of flying so that the aircraft must be always be at least 50M from the obstacle if on the flight path home.

Keeping the RTH process as simple as possible is important.
The procedure is already complicated enough by adding the backtracking.
Adding further complications would not be a good thing.

 

[DavidT_ NZ]

Am I being optimistic thinking that the drone is remaining within visual line of sight at all times ..... ? ? ? ???

 

[Dave Maine]

If it actually backtracks the last bit of the track including altitude changes, you will be fine. If you had ground clearance going in, it will be duplicated in reverse.

 

[PHZ]

Simple solution: Fly over and below the cliff but not close to anything and where it is clearly visible. Trigger RTH. See what happens and be ready to cancel RTH if you get nervous. Fly it home (or wherever).

 

[Michael Ainsworth]

It will only fly back until reconnection then ascend. If you fly down the cliff with coverage but lose connection say near the bottom the drone backtracks up the cliff to where it last had coverage. It wouldn’t fly backwards toward the cliff face but up the flight track.

 

[Meta4]

Simple solution: Fly over and below the cliff but not close to anything and where it is clearly visible. Trigger RTH. See what happens and be ready to cancel RTH if you get nervous. Fly it home (or wherever).

The backtracking doesn't happen when you iniate RTH.
It happens when Failsafe RTH is initiated.
To test that you would have to lose signal by shutting off the controller, which would mean it was difficult to cancel RTH.

 

[BobN2Tech]

If indeed the aircraft will ascend during the backtrack on a failsafe RTH as both Michael and Dave suggested, then that truly would be a well-designed behavior. It could easily be tested.

 

[NJPilot172]

@OP, have you tried PVZ's advice and activated RTH while fully in control and line of sight to observe the behavior? If so, how did the drone respond?

I'm interested in hearing the result since I'm planning a hiking trip to a mountain with some cliffs once the weather warms up.

 

[Meta4]

@OP, have you tried PVZ's advice and activated RTH while fully in control and line of sight to observe the behavior? If so, how did the drone respond?

I'm interested in hearing the result since I'm planning a hiking trip to a mountain with some cliffs once the weather warms up.

RTH behaviour is very reliable and well tested.
It should happen just as outlined in the manual.
If you haven't already experimented with it, that's highly recommended.
When you need RTH isn't the best time to start learning what it does and how to use it.