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So what could go wrong?

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#1
This is a hypothetical scenario. The Mavic Pro is to be launched from a back yard surrounded by 55’ high trees. There is an opening in the trees sufficiently large to safely reach open sky launching vertically. The flight plan is to climb to 120 meters (396’) and then proceed horizontally for one mile against the wind, which is light and gusting to 5 MPH on the surface. The flight path will be mostly-open ranch land, with random groves of trees, none of which will exceed 80’ in height, and over some small lakes. The terrain is virtually flat. The flight will take place totally over pilot’s private property, so there are no privacy issues or risks to people. Restricted air spaces are not an issue. The flight path will be visually-checked while outbound to endure no obstacles exceed 396’ in height anywhere on a potential return path. Video will be made of ranch cattle during the return flight, during which time the craft will descend to as low as roughly 50’ AGL. DJI Go 4 will be running on a Samsung 9.7” Galaxy Tab S2.

Settings:

RC Signal Lost = RTH
P Mode
Enable Obstacle Avoidance = On
Landing Protection = On
RTH Obstacle Detection = On
Smart Return Home = On

I’m not trying to wave a red flag at the VLOS crowd – this is intended to be strictly a technical question. What is the worst that could happen and how likely is it? What else could be done to mitigate the risk?
 
Last edited:

Mossiback

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#3
• The worst that can happen: Since your description means you will not have visual of your MP or the airspace, your MP may be hit by a low-flying helicopter, crop duster, birds, or any other yahoo sharing the airspace.
• How likely is it? Not very.

What is more likely is you will lose connection due to distance and trees and have to rely on RTH to bring it back.
 

ac0j

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#4
Being in side a stand of large trees, as dirklod suggests will dramatically affect range. Can you find a take off point out in the open?
 
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wytnyt

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#5
agreed,i have a row of trees about 100 tall and only get like 3/4 mile before signal degrades,los is critical for long distances
 

Mossiback

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#8
Use Litchi. Design it as a waypoint mission. Launch and forget. No worries about disconnects.
The main problem with Litchi in this case is that the OP wants to capture video of cattle on the way back. Unless they will be in a predetermined position it would be hard to use a waypoint mission for this.
 
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Lapeer20m

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#9
Mavic transmission signal easily goes miles over open terrain.

I just moved to a new place that has trees much like you describe. Transmission range is less than 1 mile for me. I was surprised how much the trees block the signal.
 
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#10
Thanks for the welcome to the forum, and thanks for the valuable information. You have a great community here. I'm not surprised that 2.4 GHz doesn't bend well around trees. I also expect the aftermarket range extenders wouldn't help much in this scenario, right? So given that signal loss is likely to happen, how reliable is signal-loss-RTH? I've been very impressed with the landing accuracy of RTH with the optical assist, but don't have any experience with signal loss. Having had a programming career, I'd guess that the algorithm to detect signal loss and invoke RTH is extremely reliable, and the problems from RTH stem mostly from obstacles encountered in flight.
 
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Thunderdrones

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#11
Thanks for the welcome to the forum, and thanks for the valuable information. You have a great community here. I'm not surprised that 2.4 GHz doesn't bend well around trees. I also expect the aftermarket range extenders wouldn't help much in this scenario, right? So given that signal loss is likely to happen, how reliable is signal-loss-RTH? I've been very impressed with the landing accuracy of RTH with the optical assist, but don't have any experience with signal loss. Having had a programming career, I'd guess that the algorithm to detect signal loss and invoke RTH is extremely reliable, and the problems from RTH stem mostly from obstacles encountered in flight.
Just have to ask, do you have DJI Refresh?
 

ac0j

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#12
Thanks for the welcome to the forum, and thanks for the valuable information. You have a great community here. I'm not surprised that 2.4 GHz doesn't bend well around trees. I also expect the aftermarket range extenders wouldn't help much in this scenario, right? So given that signal loss is likely to happen, how reliable is signal-loss-RTH? I've been very impressed with the landing accuracy of RTH with the optical assist, but don't have any experience with signal loss. Having had a programming career, I'd guess that the algorithm to detect signal loss and invoke RTH is extremely reliable, and the problems from RTH stem mostly from obstacles encountered in flight.
In MOST cases the RTH when signal loss works pretty good, UNLESS there is a compass problem.
 
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UAVNV

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#13
i did this using litchi waypoints, anticipating signal loss to the controller. story below:

I wanted to capture the view from above the trees, without risking loss of transmission with manual flying. This is where Litchi shines. Satellite coverage was spotty due to the canopy of trees.

I had the map cached in Litchi previous to the trip, when I found a suitable location, tested satellites above the canopy, flew just above the tree line to tag the lowest vertical height I was comfortable with, and proceeded to create waypoints right above my location.

 
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#16
i did this using litchi waypoints, anticipating signal loss to the controller. story below:

I wanted to capture the view from above the trees, without risking loss of transmission with manual flying. This is where Litchi shines. Satellite coverage was spotty due to the canopy of trees.

I had the map cached in Litchi previous to the trip, when I found a suitable location, tested satellites above the canopy, flew just above the tree line to tag the lowest vertical height I was comfortable with, and proceeded to create waypoints right above my location.

Nice. But as Mossiback wrote, can't anticipate where those cows will be, so need real-time control.
 

Marko9219

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#17
The main problem with Litchi in this case is that the OP wants to capture video of cattle on the way back. Unless they will be in a predetermined position it would be hard to use a waypoint mission for this.
With the details unknown to me, perhaps he could program the mission to stop, shoot a 360 pano then repeat as needed to see the areas needed. I dunno Just a thought
 

RoboticTundra

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#18
RTH does not, in my experience, fly to directly over the landing spot and then descent straight down. It will fly to the approx location +/- about 10 meters, begin descending, and adjust as necessary. If the trees are tight in to the landing area it may have difficulty.
 

colinfowler

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#20
This is a hypothetical scenario. The Mavic Pro is to be launched from a back yard surrounded by 55’ high trees. There is an opening in the trees sufficiently large to safely reach open sky launching vertically. The flight plan is to climb to 120 meters (396’) and then proceed horizontally for one mile against the wind, which is light and gusting to 5 MPH on the surface. The flight path will be mostly-open ranch land, with random groves of trees, none of which will exceed 80’ in height, and over some small lakes. The terrain is virtually flat. The flight will take place totally over pilot’s private property, so there are no privacy issues or risks to people. Restricted air spaces are not an issue. The flight path will be visually-checked while outbound to endure no obstacles exceed 396’ in height anywhere on a potential return path. Video will be made of ranch cattle during the return flight, during which time the craft will descend to as low as roughly 50’ AGL. DJI Go 4 will be running on a Samsung 9.7” Galaxy Tab S2.

Settings:

RC Signal Lost = RTH
P Mode
Enable Obstacle Avoidance = On
Landing Protection = On
RTH Obstacle Detection = On
Smart Return Home = On

I’m not trying to wave a red flag at the VLOF crowd – this is intended to be strictly a technical question. What is the worst that could happen and how likely is it? What else could be done to mitigate the risk?
I would test your RTH to see if it returned accurately and safely. Set RTH altitude with a good separation over your trees.
You can take over the landing if it dose not look safe or accurate.
 

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