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No normal descent

Discussion in 'Pro/Adv Discussion' started by JamesBandes, Sep 13, 2015.

  1. JamesBandes

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    This evening I attempted my first nighttime flight.

    I calibrated as always before take off and when I first took off I let the P3 Hover for about five minutes. I have noticed since the last firmware update that contains the new auto flight features 1.4 that sometimes the altitude and descent float. What I mean is that instead of hovering in one stationary position it sometimes is a bit fluid and floats up-and-down in GPS mode. It usually settles down.

    I climbed to about 200 feet and was shooting video and when I pulled back on the left stick to decrease altitude instead of coming down the aircraft moved forward and did come slightly down but the forward motion was much greater than the amount of the descent.

    Being my first nighttime flight it made me nervous so I decided to land. I was unable to come straight down. I had to come down a few feet and stop and correct for forward drift. Come down a bit more and again stop and correct for forward drift. I had to repeat this crazy process all the way down.

    I was finally able to successfully land the P3 but I am very curious as to why pulling back on the left stick did not cause the P3 to come straight down?
     
  2. Wibble

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    Sounds strange but sometimes you can get strange thermals and things at night that you don't get in the day. If the land is warm and the night air is a lot cooler for example.
    Of course might be another reason entirely.
     
  3. 43k

    43k

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    Sounds as if you were flying in atti mode.
    Have you checked the flight log to see if you were in atti mode?
     
  4. JamesBandes

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    It sure was strange and because it was at night I did not want to switch out of GPS mode. My spotter thinks it was the wind. It did improve the lower I went. Will test tomorrow in daylight. But felt scary to pull back on the left stick and see it go forward and only drop like 3 feet. Then had to hover correct and do it again. Was crazy.
     
  5. JamesBandes

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    That makes so much sense. I will check the logs tomorrow.
     
  6. Bryce

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    I have those same problems sometimes from a couple thousand feet.
     
  7. 43k

    43k

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    o_O
     
  8. bobmyers

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    Check the RC calibration-- may not be the issue, but worth a try.
     
  9. JamesBandes

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    Well I watched back the video on the log and it was in P-GPS mode the entire time. I watched the descent on video and it looks steady so again perhaps wind. I will try an RC calibration. So strange.
     
  10. Meta4

    Meta4 Moderator
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    As you describe it, this is a mystery.
    It is not wind or thermals. The Phantom handles winds quite well in daylight so it will at night.
    For wind to cause such a weird behaviour, you would have noticed a very strong wind.

    If you had watched the instruments, rather than the Phantom you would have been able to check it's performance, and I suspect, you would have detected that what you think you observed was actually an illusion caused by disorientation in the dark.
    Checking the flight log should show what was happening (but this might be tricky if you were descending and pulling back all the time).
    Check the Phantom in daylight.
    If it descends normally in daylight, it will in the dark.
    If it doesn't, the first thing to look into would be re-calibrating the Tx.
     
  11. 4wd

    4wd

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    I'd be checking the IMU values, it doesn't hurt to do that after firmware update anyway.
    It needs to be cool when you start the process.

    Something I've noticed when doing firmware update is how hot everything gets, I wonder if that upsets things a bit rather than the new firmware per se.
     
  12. Stan_in_KS

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    I believe the software in the Phantom applies wind correction and holds position only when the sticks are in the neutral or un-touched position. Whenever you apply a stick input the GPS position holding corrections being applied for wind correction are stopped, and the aircraft will drift down wind. For example, if you choose to fly down a street with a lot of trees and you position your Phantom below tree level, planning to cruise down the middle and get a shot of your children riding on a bicycle, for example. If the wind is calm, all will go well. If you have a 10+ mph crosswind, pushing the stick forward will allow the aircraft to start drifting sideways at 10mph, until you stop providing forward input using the right stick and the GPS starts again holding position against the wind.

    To fly a straight line TRACK, just like a real pilot you will have to provide your own "wind crab" to your aircraft's COUSE by pushing the stick forward, and adding some left or right "into-the-wind" input to correct for the wind drift. If you don't understand this "wind drift" issue, you will get an ugly lesson when your Phantom drifts to the left or right while you are pushing the right stick straight forward, and your Phantom drifts into the trees or some other object and crashes.

    In a stronger wind, descending may provide the same "wind drift" issue when you are pulling back on the stick. When you stop descending the GPS wind correction is reapplied to hold the Phantom in position.

    I could be wrong about this, but you might be able to test it by starting a hover at say 20 feet in a strong wind, and then pushing only the left stick to climb straight up to a couple hundred feet, and then descend straight down using only the left stick. If, while flying in a strong wind, the Phantom returns to its original position, the GPS wind correction is being applied during the climb and descent. Now if your right control stick is out of calibration, it might provide the slight drifting downwind symptom, because the software assumes you are providing a small right stick input. Try recalibrating your RC controller with the Go App and see if this stops the drifting during straight up and straight down, left-stick-only operations.
     
  13. Meta4

    Meta4 Moderator
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    Yes .. I think you're wrong. The Phantom doesn't stop holding position while descending.
    It has GPS and a bunch of sophisticated sensors and programming to hold position whether flying, descending or hovering.
    If it did work the way you've described, it would be causing crashes all the time - and it isn't.
     
    43k likes this.
  14. JamesBandes

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    Thanks I suppose it will remain a mystery. I took off today (wind was strong) only 8 satellites. I climbed only to about 49 feet and tested extensively and all responded normally. I did do a RC calibration before flying.

    I did once again observe a lack of holding vertical position. It will just drop or rise a foot or two on its own. It usually stabilizes if I just let it hover for 3 or 4 minutes

    I also shortened my control sticks until my pilot skills improve.

    Thanks everyone.
     
  15. JamesBandes

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    So today I took the drone out to a huge 400 acre field and did confirm after flying to an altitude of 400 feet that upon descent the drone does not come straight down. I suspect that winds at higher altitudes are to blame. At low altitudes it does not appear to be an issue. I did recalibrate the RC and the IMU so it must be the wind.
     
  16. Bryce

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    The wind shouldn't matter.. it's coming down a virtual tunnel, depending upon how many sats you can see, it should be a 2 foot wide tunnel. If it's outside of that, then there is something not quite right with how you are bringing it down or something wrong with it internally.
     
  17. Meta4

    Meta4 Moderator
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    Wind should have no effect unless it is blowing faster than the max speed of the Phantom.
    Your Phantom can easily hold position in 20+ mph winds.
    If you are manually directing the descent it might be the way you hold the joysticks.
    Try triggering RTH and see how it comes down with no input on the controls.
     
  18. snowghost

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    Your OP says you always calibrate before flight. I don't think that's very wise. Just check the values in the app. Otherwise you are susceptible to calamity.
     
  19. JamesBandes

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    I no
    it saw 14 Sats and is solid as a rock except on descent. It's not too bad but pulling the left stick straight back does not bring it straight down I need to compensate with the right stick. So strange.
     
  20. JamesBandes

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    Thanks I will give that a try