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Standard Litchi: Waypoints - altitude above and below take-off point?

Discussion in 'Phantom 3 Help' started by GrahamStokes, Apr 16, 2016.

  1. GrahamStokes

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    I really like this app, it has been working very well for me (and I would happily have paid 2 or 3 times more for it). I have a question concerning setting the Altitude for Waypoint Missions. Until now, I have been using it in relatively flat open spaces where the ground elevation doesn’t vary a great deal and I easily understand that in this situation setting the Altitude of a Waypoint will determine the height of the aircraft above the take-off point (i.e. ‘ground level’). However, I should like to plan some missions in hills and cliffs near to the sea, where the ground elevation varies considerably from 0 at sea level to hundreds of feet about sea level on the hills and cliffs.

    Here is the point that I am not sure about. If, for example, I were to take-off from a hill top that is, say, 200 feet above sea level and set the Altitude of the 1st Waypoint as ‘100 feet’, then at the 1st Waypoint the aircraft will be 100 feet above ground level and 300 feet above sea level – I believe that this is correct. Next, if the setting for the Altitude of the 2nd Waypoint, which is some distance away over the sea, is kept at ‘100 feet’, will the aircraft simply fly horizontally at a constant 300 feet above sea level and, therefore, will still be at 300 feet above sea level when it reaches Waypoint 2, or will it descend as it flies to Waypoint 2 and will end up at 100 feet above sea level, but 100 feet below the take-off point?

    I could try this as an experiment to find out, but getting it wrong could be disastrous as I am a little reluctant to accidentally drop it into the ocean or fly it into the side of a cliff because I have misunderstood the Altitude Setting. I was wondering if anyone knew for certain how it would behave in this type of situation?
     
  2. Sagebrush

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    You're elevation is always AGL from your takeoff point. If you mission starts at 200 AGL and your'e waypoints are at 200 feet and there's a hill that in the way and 300', you'll hit it.

    I agree, great app.

    Sagebrush
     
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  3. GrahamStokes

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    Sagebrush, thank you for your reply. “Your elevation is always AGL from your take-off point . . . ”, so the aircraft altitude in the Litchi app is always measured relative to the take-off altitude – that is what I thought, and it is good to have it confirmed before I go out and try it.

    Therefore, to achieve the situation that I suggested, in the example above, for the aircraft to end up at 100 feet above sea level at Waypoint 2, from a take-off point at 200 feet above sea level, I should need to set the Altitude for Waypoint 2 as: ‘-100 feet’?! (This is what I want it to do – to fly down the hill to the sea and then come back up to land.)

    A feature that I’d like to be added to the Litchi App is the ability to be able to specify different speeds of travel between the Waypoints. So, for example, if the aircraft had to fly some distance to get to a Point of Interest, you could set a high speed to get it there, then set a slow speed at the Point of Interest to capture your video and then set a high speed again to get it home. I know that you can increase the speed during a Mission by using the Forward Stick on the Controller, but it would be nice to be able to pre-set that. (Perhaps the Phantom 3 is not able to store travel speed data between Waypoints?)
     
  4. Sagebrush

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    Yes, If I understand correctly. I'd suggest you fly it conservatively first. Start with -50' and be ready to abort by toggling to GPS mode.

    Also, you can increase your speed between waypoints with your right stick. The maximum is set in your missions settings.

    S

     
  5. kpuk

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    You can plot your course on Google Earth, export to KML and import into the Litchi hub. That uses actual altitude rather than always relative to the starting point.
     
  6. neild

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    Could anyone explain to me how to do this ?
     
  7. Sagebrush

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    Yeah this guy can.



    It works well.

    SB
     
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  8. Richard R

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    Read page 22 in the manual. Speed can be set for each waypoint. Sets the speed that the aircraft will have when it reaches that WP. It will automatically speed up or slow down accordingly.
     
  9. Sagebrush

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    Yes, but be careful. If you go from a WP at 50' to a WP at -100', the bird will descend as it moves laterally and If there's a still cliff in that descent you'll have a bad day. Make sure your WP2 is outside the cliff and then do a descent to WP3.

    "I was wondering if anyone knew for certain how it would behave in this type of situation?" Yes, I have flown Litchi missions with WPs less than 0.

    Like I think I said, always keep your left trigger finger on the switch to stop the mission.

    SB
     
  10. neild

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    Spot on , thanks
     
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