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Flying below takeoff level ...

Discussion in 'Cinestar Misc' started by Sebastian Meredith, Jul 18, 2013.

  1. Sebastian Meredith

    Sebastian Meredith Active Member

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    Hi all.
    We're doing a shoot in a very deep ravine/gorge (+- 150meters) but accessibility to the base is not possible so we have to shoot from the top and fly down to the bottom where the river is.

    My question is about the altitude readings and gps data. When setting the ACC before take off (left stick top left) setting altitude position to zero... how does the telemetry and altitude reading behave/adapt to being below zero?

    Should fail safe come into play ... Will it cooperate?

    Or does everything work as per normal ands just give a negative altitude reading? Does PH and AH behave as per normal?

    Any advice would be appreciated.
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Sebastian: Interesting questions. I'm not sure I've seen negative altitudes displayed. It wouldn't be too hard to test it, though. If you can find someone with a first floor deck, take off from that and land on the ground and check the GPX file. Alternatively find some local high ground, take off from that and land lower down as a mini-simulation of the ravine.

    As to the Emergency Come Home -- my guess is that it will climb to the height you set, so it would climb out of the ravine up to X meters, where X is the value you set.

    Lets hope that the MK guys contemplated having the height be a signed numeric value.

    Please do post the results you find.
    Andy.
     
  3. Tyler Olson

    Tyler Olson Member

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    When I've used the Come Home command it appeared that it gradually rose the correct height as it flew back. As apposed to step 1: fly to correct height, Step 2: come home. In that case you'd probably fly into a canyon wall on the way home.
     
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  4. Sebastian Meredith

    Sebastian Meredith Active Member

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    Thanks Andy & Tyler ...
    I'll do some tests on the weekend and report back after ...
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Tyler is correct. The source code calls for an ascent or descent to the CH preset altitude en route home rather than a vertical ascent/descent followed by horizontal flight.

    Andy
     
  6. Sebastian Meredith

    Sebastian Meredith Active Member

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    Well I hope there is no need for fail safe to kick in or CH tone activated! Staying clear of cliff faces will be preferable....
     
  7. Gary Haynes

    Gary Haynes Administrator
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    Andy isn't the first 5 seconds solely a vertical ascent/descent to CH height followed by horizontal flight?

    • First at all the function "PositionHold" will be activated for 5 seconds and the Kopter climbs/falls to the preset "ComingHomeAltitude". (note: only if the distance from the starting point is >25m)
    • After the 5 seconds the function "ComingHome" will be automatically activated and the Kopter flies back into the direction of theHomeposition (Start Point).
      (If the set altitude shouldn't have been reached within the first 5 seconds increases or decreases the Kopter its altitude during the flight back.)


      http://www.mikrokopter.de/ucwiki/en/FailSafe?highlight=(come)|(home)
     
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  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Gary: Yes. The first five seconds is used that way, but, if the copter does not reach the CH preset, it starts to come home regardless, climbing or descending en route -- as your last bullet item says. So the concern would be if the copter is at -100 meters with a CH preset of, say, 20 meters, and ECH triggers, then the copter will have to climb 120 meters in the 5 second period. If, for some reason it doesn't make it, then it will start coming home, climbing en route.

    I've not tested the max climb rate of the C8, so I'm not sure whether it would make the 120 meter ascent in five seconds (a climb rate of 24 meters per second, 53 mph). Somehow, I have my doubts! :)

    Andy.
     
  9. Sebastian Meredith

    Sebastian Meredith Active Member

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    Hi guys, thanks again for the feedback and input. Although the ravine is approx 100 - 150m deep the chances of copter being close to the ground is very slim, most of the flying will probably take place halfway down.. Should we go lower it will most probably be to do a direct climb up to shoot the face of the ravine on its way up. So I feel much more comfortable should FS kick in while during the general flight, which should give it enough time to climb to a safe height before returning to base.. Should we be on a cliff-face ascent at the time something goes wrong ... Well then all I hope it that the insurance kicks in :)

    But hopefull the shoot runs smoothly without incident ....
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Good luck, Sebastian....I'd very much like to see the GPX file from a "ravine flight" if I may. Would you consider posting it please? I'd like to see how the MK firmware handles the negative heights. (Note: I'm using the word "height" meaning distance above/below ground, rather than "altitude" which is typically measured from mean sea level -- but can also, of course go negative! Parts of Death Valley, CA are -280 feet altitude!)

    Andy.
     
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  11. Sebastian Meredith

    Sebastian Meredith Active Member

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    Definitely Andy.
    We'll be shooting from this coming Monday for 3 days. So I'll upload some data towards the end of the week.
    Would be great to have a diagnostics on the flight logs.
    Thanks.
    Sebastian.
     

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