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Clarification of OA behavior on RTH & max altitude
847 8 2016-9-23
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brunobaptista55
Second Officer
Flight distance : 1369839 ft
Brazil
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Hello,

I´ve searched this and other forums, as well as the manuals and could not come up with a definitive understanding.

Let´s say that I have my max height set to 120m, and my RTH height set to 60m. What happens if during a RTH (with Obstacle Avoidance turned on) the aircraft encounters an obstacle say 90m high? I expect it to climb to 95m (5m above the obstacle as in the manual) and as long as it does not hit the 120m maximum height it will continue to RTH.

So the maximum height of an obstacle that it would avoid is 5 meters less than the maximum height set (in this case 120m maximum minus 5m clearence thus 115m).

In the situation that it encounters an large obstacle (such as a building) that it could not clear vertically within the max height set, it would hover, and eventually auto-land at the critical battery level.

Is this the way it works?

Thanks.
2016-9-23
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vuzfrKtLUZZP
lvl.2

United States
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Hello, I am new to the form. This is a good question and I have not tested the drone to this extent. I am interested to see what other people have to say. In the Return to Home mode you still have control (up "to the max height set", down, left, right) over the drone. I believe that you are correct with everything but in the situation in which the obstacle exceeds the max height set on the drone you can fly the drone to the left or to the right around the obstacle and once cleared the drone will then continue forward to the Return to Home point.
2016-9-23
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labroides
Captain
Flight distance : 9991457 ft
Australia
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If you fly where you may have to RTH with a max height and/or RTH height that is not clear of any obstacles on your RTH path, you are asking for trouble.
Setting appropriate heights before flying is the most effective and reliable method of object avoidance.
2016-9-23
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DJI-Ken
DJI team
Flight distance : 1515312 ft
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That's the way I think it would work.
That's why you set your RTH way above any possible structure that can get in the way.
It may auto land onto a busy intersection, there's no reason for this to happen and if it did it's totally pilot error.
2016-9-23
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labroides
Captain
Flight distance : 9991457 ft
Australia
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vuzfrKtLUZZP Posted at 2016-9-24 07:21
Hello, I am new to the form. This is a good question and I have not tested the drone to this extent. ...

In the scenario given, the Phantom would be in RTH because it was flown behind an obstacle and loses control signal.
In that situation, you would have no control.
It is important to think before you fly and avoid flying behind obstacles and if you do, you must plan for it.
Trusting OA to do it all for you is a good way to go home without a Phantom.
2016-9-23
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Kneepuck
Captain
Flight distance : 275105 ft
United States
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I will put in my 2 cents and stress what labroides has said.  Poor planning and understand has brought down more Phantoms than all other reasons combined,  easily.  A max height set lower than the possible necessary rth height is asking for trouble with a big megaphone,  and you will surely get what you are asking for sooner or later.
2016-9-23
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brunobaptista55
Second Officer
Flight distance : 1369839 ft
Brazil
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Thanks for all the contributions.

I couldn't agree more that proper setting of the RTH height above the highest structure of the flying area is a good practice.
Also proper planning and flight discipline is fundamental.

I am not proposing to set the RTH/limits as in this example. I am just really curious of how it was programmed in the OA logic.
I strongly agree (and practice) what labroides, Kneepuck and DJI-ken recommend. But I also like to know how things work. Knowledge is always good to have.

Safe flights.
2016-9-23
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vuzfrKtLUZZP
lvl.2

United States
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Thank you labroides for the clarification about the lost of radio connection and I agree that your max height should be set at whatever the legal maximum height is for your country along with if you're even allowed to have it out of sight.  
2016-9-23
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Bilzc10
lvl.4
Flight distance : 351575 ft
United States
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i dont have this problem with my phantom 3, my trusty ol p3 will always crash if it heads towards an object during RTH. I don't have to worry about "will it be able to ascend past the object this time?", because it wont!
But i always set a good rth altitude, and have max height set to the highest value, because i can control myself, but always have the option to climb higher in emergencies without first going into settings.
2016-9-23
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