Welcome to PhantomPilots.com

Sign up for a weekly email of the latest drone news & information

Negative AGL

Discussion in 'General Discussion' started by b0dyr0ck2006, May 6, 2016.

  1. b0dyr0ck2006

    Joined:
    Jun 5, 2015
    Messages:
    64
    Likes Received:
    52
    Location:
    UK
    If you took off from the top of a mountain and flew down hill, how far would you be able to go? Would the quad be limited to -500m?
     
  2. Malakai

    Joined:
    Feb 29, 2016
    Messages:
    190
    Likes Received:
    73
    Location:
    Wolves, UK
    try taking off from a flat shed roof or wheely bin and land on the ground. let us know what happens :)


    Sent from my iPhone using PhantomPilots mobile app
     
  3. b0dyr0ck2006

    Joined:
    Jun 5, 2015
    Messages:
    64
    Likes Received:
    52
    Location:
    UK
    I know you can fly in negative AGL. My question is how far will the software let you go?
     
  4. N017RW

    Joined:
    May 2, 2014
    Messages:
    6,244
    Likes Received:
    1,614
    Location:
    Palm Beach Co.- FL
    There's no limit.
     
  5. Meta4

    Meta4 Moderator
    Staff Member

    Joined:
    Jan 8, 2014
    Messages:
    7,745
    Likes Received:
    3,457
    I've seen people suggest there is a limit but never seen anyone test it to confirm.
     
  6. b0dyr0ck2006

    Joined:
    Jun 5, 2015
    Messages:
    64
    Likes Received:
    52
    Location:
    UK
    It would be interesting to know, theoretically there should be the same limit both up as well as down
     
  7. N017RW

    Joined:
    May 2, 2014
    Messages:
    6,244
    Likes Received:
    1,614
    Location:
    Palm Beach Co.- FL
    No, there's no theory to support this nor is there any cause for it.

    Limits must be expressly created and there is no need for such a thing.

    Worst case is you exceed the sensor's max pressure and it remains at that value/level.
     
    jonebk12 likes this.
  8. b0dyr0ck2006

    Joined:
    Jun 5, 2015
    Messages:
    64
    Likes Received:
    52
    Location:
    UK
    Ok, let's suppose you go to the top of the burj khalifa. You take off from the roof and the quad sets your AGL at 0. You then to proceed to fly down the outside of the building (829.8 metres tall). Would the quad plateau at 500 metres or continue to the bottom?
     
  9. N017RW

    Joined:
    May 2, 2014
    Messages:
    6,244
    Likes Received:
    1,614
    Location:
    Palm Beach Co.- FL
    There's no limit.

    You should be able to derive the answer from that statement.

    Why do you choose -500M? Why not -550, -220, -1000, -15000?

    There's no limit as there is no need for such.

    Please post any DJI documented information to the contrary.

    The 'folklore' being generated here does not count.
     
  10. b0dyr0ck2006

    Joined:
    Jun 5, 2015
    Messages:
    64
    Likes Received:
    52
    Location:
    UK
    Perhaps I have read the tone of your message wrong, I'm looking for actual documentation or proof, not supposition. I'm not going to read between the lines and create my own answer for 'limits must be expressly created and there is no need for such thing' as a definite no limit.

    The reason I 'chose' 500 metres is because that is the maximum flight height, so logic would dictate -500 metres.

    Using my example of flying off of the burj khalifa you could in essence fly around Dubai at at height of 1329M which is obviously well above the regulation
     
  11. N017RW

    Joined:
    May 2, 2014
    Messages:
    6,244
    Likes Received:
    1,614
    Location:
    Palm Beach Co.- FL
    The pressure sensor is relative not absolute. It has no idea of true altitude against any datum.

    When you take off from whatever building or structure you choose the a/c will assign that baro pressure to Zero feet in altitude. So yes you can fly another 500m above that point.

    What you call 'logic' in that there must be an equal negative limit, I call supposition.

    Please give an example why you feel there is a logical need for a limit?

    I can think of no reason to prevent an a/c from landing as such a [negative] limit would create.
     
  12. sar104

    Joined:
    Mar 22, 2014
    Messages:
    1,265
    Likes Received:
    245
    Location:
    Los Alamos, NM.
    The 500 m limit (specifically the 500 m above takeoff point limit) does not correspond to any regulation, so trying to relate them is pointless. And yes - if you can find a high point to launch from, whether it be a mountain or a building, then you can fly over nearby, lower-elevation areas at an altitude above 500 m AGL. That's not inconsistent, since the 500 m limit is not an AGL limit in the first place - the aircraft does not know its height above the ground.

    In terms of a negative (again relative to takeoff) limit, the point being made is that none is documented and there is no operational reason why one would be needed, and so why would one have been added to the firmware? Invoking altitude symmetry around the takeoff as a reason to expect one makes no sense, since up is not equivalent to down in terms of the hazards it presents.
     
    N017RW likes this.
  13. matti

    Joined:
    Mar 15, 2016
    Messages:
    401
    Likes Received:
    62
    FWIW Litchi's minimum BGL is -200 m (Below Ground Level). Don't know about DJI FW and GO app.
     
    b0dyr0ck2006 likes this.
  14. Phantomfreak

    Joined:
    Dec 12, 2015
    Messages:
    196
    Likes Received:
    70
    Using The GO app I've had both the P3P and P4 at 185 ft. below takeoff point, with no issues, error messages, or anything out of the ordinary. The app displays height as a negative measurement.


    Sent from my iPad using PhantomPilots mobile app
     
    b0dyr0ck2006 likes this.
  15. gringorio

    Joined:
    Sep 26, 2014
    Messages:
    241
    Likes Received:
    70
    Location:
    Tucson, AZ
  16. Othan1

    Joined:
    Jun 26, 2015
    Messages:
    222
    Likes Received:
    62
    It is possible that they did not code for large negative numbers and the OP simply wishes to know if anything had been QA'd and can be empirically detailed.
     
    b0dyr0ck2006 likes this.