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RTH altitude in the mountains

Discussion in 'Pro/Adv Discussion' started by Steve_in_NJ, Aug 22, 2016.

  1. Steve_in_NJ

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    I am about to fly a Litchi mission that I created originally in Google Earth. I will be flying up and down the side of a mountain to an elevation that is about 500 feet higher than the home point. The craft will fly at a constant 150 foot altitude AGL, thanks to Google Earth. My worry is, do I need to set the RTH height higher than the highest point on my mission? That would mean a 700 foot RTH height. I am guessing the answer is yes but I thought I would throw it out there. Thanks!

    Since this is a Litchi mission the craft will fly on despite being disconnected from the radio (which I do not believe will happen), so the only reason for a RTH to happen is if I push the button.
     
  2. Grandpa Don

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    Damned if I know! But I do have a question. Tell me how you use Google Earth to create a mission. I would be very interested in that. I use GE all the time for other things.
     
  3. BigAl07

    BigAl07 Moderator
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    That's a tough one. It's going to be hard to remain within "guidelines" on that one. Should you get the RTH altitude to be 100' over the highest obstacle you would in theory be flying 600' AGL at certain points.

    With that being said I don't think you have much of an option except to do exactly that.
     
  4. happydays

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    If the phantom is above what you have set the RTH at, it will return at that height. Say you have the RTH set at 60', and you're away up there at 500', it will RTH at 500'. It's only if it is below this height that it will climb up.
     
    toegema likes this.
  5. sonof40

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    Litchi & GE
     
  6. Vichian-Bruno

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    I created a short document explaining how to create a mission in GE relative to ground, how to save and import into Litchi.
    Have fun!
     

    Attached Files:

    Oso likes this.
  7. Richard R

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    Excellent, Thanks for the work. Looking forward to trying it out.
     
  8. Grandpa Don

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    Wow! I did not know that! That's good to know.
     
  9. Kamloops

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    Nicely Done!
     
  10. royster

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    Very good info- I;m about to fly from my place, which is highest point around, to a local park which is 30-50 m. lower than my location. Starting off from my place at 30 m. I'd be fine.
    But, beginning at the park, at 30 m. & heading to my place I had thought, my bird would follow the elevation of the ground to my place.
     
  11. WetDog

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    Common misconception. The Phantom's ONLY way to determine altitude is through the barometer. The barometer is set to zero when you take off. It has no idea what's below it. If you set the altitude at 200 feet and fly into a hill, it will bee line directly into the hill. To put it another way, Phantom altitudes are always absolute. They are never relative to the ground (insert old Sith joke here).

    Newbie folk often assume that Phantoms use GPS for altitude. Turns out that anywhere near ground, that doesn't work all that well at least for consumer grade gear. There are ways around it but it costs real money. Maybe in the Phantom 6 they will put an x-band radar in so you can determine actual altitude over ground, but for now all we have is the barometer.

    But all is not lost nor evil if you have to set your RTH height to something over 400 Above Ground. Yes, if you lose RC contact, the aircraft will ascend to that altitude and head home, but somewhere along the way you are very likely to regain control. You can then bring the craft down to a safer altitude.
     
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  12. Richard R

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    And just like on a real plane, the barometer can be affected by weather induced pressure changes, although those don't usually happen significantly over the course of normal battery charge duration.
    Heck with x-band, why not a simple laser rangefinder (LRF)? For the ranges that we need, a simple, eyesafe LRF would only weigh an ounce or two and take almost no battery power. Replace the sensors in the VPS?
     
    sonof40 likes this.
  13. Avocet

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    Over in Parrot land ... us BeBop owners were/are plagued by a barometer that was seemingly sensitive to changes in light. The body/nose cones (where the barometers are located) of the BeBops are lightweight dyed styrofoam and when you flew in or out of shadows and sunlight, this would create a meter's worth of rapid ascent or descent. The mod was to open up the Bop and cover the barometer with some light foam and/or paint the interior surface of the nose cone with a permanent marker. Did the trick it did. I don't see my p3p being susceptible to this thank goodness.
     
  14. WetDog

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  15. jtludwig

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    How would the Phantom possibly know the contours or change in ground elevation as it flats around?

    It's not like it has a built in topographic map.


    Sent from my iPhone using Tapatalk
     
  16. Steve_in_NJ

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    Happy to report that the mission went perfectly. I am uploading to youtube now on a dirt-slow connection. Will post ASAP.

    BTW when flying a mission like this, care must be taken to be sure that the max altitude is set high enough. There's more than one place to do that. You'll know you are good when all the alts in all the waypoints are showing what you expect them to - check them while connected to the craft. If they say no more than 400 (or other earlier preset max) you're not ready.
     
    #16 Steve_in_NJ, Aug 23, 2016
    Last edited: Aug 23, 2016
  17. Steve_in_NJ

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    OK here it is!
     
    #17 Steve_in_NJ, Aug 23, 2016
    Last edited: Aug 24, 2016
  18. captirwin

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    Heres a youtube link.
    very good...