Alta dives after a few meters in height mode

Discussion in 'ALTA' started by Jonas Westling, Feb 11, 2018.

  1. Jonas Westling

    Jonas Westling New Member

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    Hello Freeflyers! After buying my (used) Alta last autumn I've now done some test flights and learning of flying the aircraft.

    Something I've noticed when flying low (2-3m above the ground) in height or position mode is that after a few meters of forward pitch (about 20m?) the aircraft dives or somehow loses height and I have to abort the forward movement, apply throttle (sometimes after switching to manual mode) to gain safe height again.

    I noticed this the first time when it was around -13 celsius, and I thought it might have been the batteries, but that doesn't seem to be the case. The aircraft flies very nice in manual mode. I also feel like the position mode isn't as stable as earlier, like it's a bit confused sometimes, and I'm losing my trust in it, which was good earlier...

    I have the default tuning values and latest firmware.

    MoVI M5, Connex, C100 mkII: 4120g
    2x TATTU 7000mAh batteries: 1815g
     
    #1 Jonas Westling, Feb 11, 2018
    Last edited: Feb 11, 2018
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Jonas:
    Sorry to pepper you with questions but it's hard to answer your question without a little more information:

    How aggressively are you forward pitching the ALTA?
    How much height is the ALTA losing? (I infer you're doing this on level ground! :) )
    When you stop the the forward pitch, does the ALTA remain at the "new" height above ground, or climb back up to the original height?

    Thanks
    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  3. Jonas Westling

    Jonas Westling New Member

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    Hi Andy, thanks for replying!

    I the beginning when i encountered this problem I was pitching fairly aggressively on a frozen lake with snow on it. But since then I've also been flying near my home on a small narrow road where it wasn't aggressive at all.

    I'm loosing enough height to crash into the ground, I've actually left some marks from the landing gear legs in the snow... Both the lake and street are level ground, with more or less snow...

    When I stop the forward pitch it's not ascending back up like it would when flying fast and aggressive in manual mode. I had the experience of both the Alta and my small practice drone descending in high speeds, but this seems different. Maybe I have to test this further...
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hmm. Well, typically the descent's cause is that the vertical component of lift is reduced when the ALTA is not level, but if you are in Height Hold, that should compensate for the reduced vertical component by adding power -- of course there comes a point where, if the ALTA is canted over too far then no amount of power will prevent it descending.

    Out of curiosity, what do you have the Climb Rate Clamp set to? I'm not suggesting that's the cause or the fix, just curious.

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  5. Jonas Westling

    Jonas Westling New Member

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    The tuning values are default so climb rate is set to 3m/s, and I don't use the clamps, but I have tried them to see how/that they work.
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Understood. But are the clamps currently set to minimum or maximum or somewhere in between?

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  7. Jonas Westling

    Jonas Westling New Member

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    Maximum :)
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    OK. And with apologies for banging on about this, so if you press the U.Mon/Menu (right hand silver button on the Futaba 14SG), and get to the servo monitor screen, what number is showing at the bottom of the vertical display for channel 7? Is it +100 or -100?

    On my Futaba, with the left slider (underneath the Futaba on the left side) rotated to the upper-most position (furthest away from your body if you hold the transmitter normally), it should be display -100 for channel 7. Do you see the same thing?

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  9. Jonas Westling

    Jonas Westling New Member

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    No problem, I'm grateful for all the help Andy!

    It says -100 for channel 7,
    tho it seems to be inverted in two ways compared to yours... When i hold the Futaba and adjust the slider accessible to my left hand it shows as channel 8, and when I move it up or further away it goes from -100 to +100. The same for channel 7 but with my right hand...

    edit: I changed this in the Futaba now so it works like yours, but I'll have to check the mapping in the app also..?
     
    #9 Jonas Westling, Feb 11, 2018
    Last edited: Feb 11, 2018
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    That's odd -- it seems as though the Model file you have is different from one FF installed in my Futaba 14SG.
    So it would seem that the sliders are transposed and the sense of them is not reversed.

    I'm just wondering what the effect of this sense reversal will be on the original phenomenon....transposing which clamp slider does what isn't the issue -- it's the sense reversal that you thought the clamps were at maximum speeds, when I suspect they were at minimum speeds.

    There's the final question of whether this is actually the problem or not, of course....and unfortunately you'll need to go and fly to verify whether this is the case...

    Let me know what you find...
    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  11. Jonas Westling

    Jonas Westling New Member

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    I will do another test flight later this week, tho I doubt this is the real issue, but it's good to get it sorted either way...

    When I bought the aircraft the right slider was controlling the throttle clamping and the left controlled pitch, so I changed that in the app, but I will switch it back (in the app) now when I corrected it in the Futaba. When I've tried this stuff I've always flown by feeling, and It's very hard to get mistaken when comparing -100 and +100 while flying, but I will double check and see what happens. Maybe I have adjusted the throttle clamp by accident while flying..?
     
  12. Jonas Westling

    Jonas Westling New Member

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  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The left slider controlled PITCH? Really...usually those sliders control climb velocity and horizontal velocity clamps. Sounds like someone really got "creative" with the model file. Do you need a fresh copy of the FF "standard" model file?

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    So you notice a difference when flying backwards or forwards? Interesting. I didn't realize that.

    Also, have you seen this "drooping" (as Tabb called it) when you fly above ground effect -- e.g. at 10m (~30 feet above ground)?

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  15. Jonas Westling

    Jonas Westling New Member

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    Yeah if it's possible that file would be nice.

    Well, I haven't tried it that thoroughly, but no, I haven't had those problems while flying backwards, only forwards, tho I fly mostly forwards on low height...
    Yes, I've only experienced the "drooping" at lower heights that I'm aware of.
     
  16. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    See https://freeflysystems.zendesk.com/...a-14SG-Configuration-File-available-for-ALTA- for the model file. (I flunked the test -- I had to ask an FF support mage, Adam Henley....I should have just asked Mrs. Google!)

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
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  17. Jonas Westling

    Jonas Westling New Member

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    Ok, so this happened:


    I wanted to document the described behaviour of the Alta. First I flew around making sure the aircraft was working normally, which it was. I then tried flying low after a small road in 'height mode' and the Alta lost height. I usually abort the pitch and instead climb to a safer altitude, but this time it seemed to stay at the new lower level, then it lost height again and crashed...

    I'm currently in contact with the support team.
     
  18. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Ouch. Note that you were flying in "ground effect" so weird things can happen. I realize it's too late to do much good now, but I would have done the test at a height of about 60 feet above ground -- otherwise known in the RC world as "two mistakes high" (enough height to allow you to recover from two mistakes).

    It does not seem like you were pitched over that much, so disregard what I said about vertical component of lift as I don't think that's a factor.

    I could not see (because of the snow being kicked up by the rotorwash), but doesn't the road rise up in the distance -- might that have been a factor too? (As in the terrain coming up to meet the ALTA?)

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  19. Jonas Westling

    Jonas Westling New Member

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    Yeah, not fun.

    I don't think the road rises up, if that's the case it wouldn't be by very much, and you can clearly see how the Alta loses height quite fast... There are no problems flying like this in manual mode, and I think it might be something that has to do with the Alta getting confused because of the ground effect and air pressure, an engineering issue...
     
  20. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yeah, that's certainly the effect of flying sideways -- the airflow over the aircraft can alter the measured air pressure and, if the air pressure is sensed as dropping, which is usually the signal that the ALTA has gained altitude, I suspect it reduces power to compensate. The whole problem is exacerbated when you're in ground effect as the aircraft is sitting on top of a bubble of higher pressure air caused by the rotor downwash being sandwiched between the ALTA and the ground -- and when you move sideways that bubble wobbles as the ALTA moves into undisturbed air and reforms the bubble. That wobbling makes the sensed air pressure very unstable...

    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limit™
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     

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