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Movi out in open sea.

Discussion in 'MōVI M10' started by Charles Lim, Oct 13, 2013.

  1. Charles Lim

    Charles Lim Member

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    Just did a night shoot with the Movi out in open waters. In Choppy conditions.
    We sailed out with the gyro switched off. When we reached the location and tried to start the movi the gyros failed to work and the system did not want to come to life. I though perhaps there was a loose wire, was checking through the system and gave up. We sailed to an area which was calm with a harbour for a swim to cool off our frustrations. But as the conditions were calmer when we switched the gyro again and it is started working!
    We kept it on, moved to location and nailed the shots. The system worked great. Keeping a flat horizon, in choppy seas.
    I was wondering, from this situation we learnt that
    The gyros sensors have a problem trying to initialise when in a chaotic environment such as a rolling boat in open seas. Wonder whats the reason for this and if there is anyway to overcome this problem.

    Other positive . The lipo powered system gives it a incrediblity long operation duration. Enough for me to sail 1 hour to location , 1 hour shoot , and 1 hour back. And the batteries was still healthy charged up.
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I'm pretty sure the reason is that when you first power up the MoVI, the inertial motion unit in the controller needs to figure out which direction "down" is (the so-called gravity vector) -- and it cannot do that when a rolling boat alters the gravity vector all the time.

    You might have better luck if you could suspend the MoVI by a cord, prevent it from swinging like a pendulum, but allow gravity to keep it horizontal. Worth a try....but I'm not 100% convinced it would work.

    Andy.
     
  3. Charles Lim

    Charles Lim Member

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    This makes a challenge if the system needs to restarted in open sea. No the hanging idea is not going to work also. Hahaha this is my 3rd shoot to shoot this lighthouse , i tried stedicam . tyler gyro ..... and the movi started scary but it nailed it . the rest was a total failure.
    The nice thing was that I was able to so 15fps 1/15 shutter - longer exposure to capture the faint beam of the lighthouse, with nice non motion blurred images.

    yea the pendulum idea, as a person very experienced as a sailor, will not work.
     
  4. Charles Lim

    Charles Lim Member

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    So i guess it's for the system to hold lock with gyros. the motors need to be active. No point developing a feature to initialise the gyros with motors off, to be turned on only when at location at sea.
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Indeed. It's a challenge. It's all Einstein's fault. He was the first to point out that gravity and acceleration are indistinguishable, I think. Thus, I suspect the MoVI cannot determine the gravity vector when it's being subjected to other accelerations.

    Andy.
     
  6. James Leonzio

    James Leonzio Member

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    I noticed a similar symptom when experimenting with an overslung setup. I needed to start up in the typical underslung config, then flip the MoVI while on, in order to get a functioning overslung config.
     
  7. Charles Lim

    Charles Lim Member

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    thx for the swift answers andy . is there anyway to have a hot swap lipo power system just in case! i need to change the batteries for a job in the sea?
     
  8. Charles Lim

    Charles Lim Member

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    another question - should i 'tune' the system with all this shaking going on in the boat?
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    If you use two or more of the MoVI batteries that you parallel charged (so they were balanced to be at the same voltage), you could extend the life of the LiPo installed on the MoVI, disconnecting the external LiPos when you were at the right location. The problem would be that if you were to use the MoVI for a while, then the installed battery's voltage would drop and there would be large current flow if you connected up the external LiPo's to transit to another location -- the external LiPos would "flash charge" the installed LiPo (with the emphasis on the "flash" if the current flow was too high).

    Perhaps a better way would be to have some larger capacity LiPo's in a belt pack and have them connected up as the sole power source, and of sufficiently large capacity that you never powered the MoVI off. You'd need to get a cable from the belt back to the handle-bar, and then a thin, flexible cable down to pan-part of the MoVI so that it didn't impede the ability to pan.

    I would tune the MoVI for hand-held operation by hand-holding it -- but I don't think you gain anything (other than the opportunity to get sea-sick) by tuning it while it's rolling and pitching on the boat. I could be wrong on that though.

    Andy.
     
  10. Brad Meier

    Brad Meier Active Member
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    You can also initialize the MoVI with the mode switch on the controller in the off position. This will leave the motors powered down while keeping the IMU and bluetooth powered up. When ready to shoot, flip the mode switch to majestic or dual and the motors will then be powered. It'll save some battery.
     
  11. Joe Frohriep

    Joe Frohriep New Member

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    yep. it's physics. Same when aligning intertialbased navigation systems on aircraft. There is some tolerance for movement, but not much due to mentionend problem.
     
  12. Gary Haynes

    Gary Haynes Administrator
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  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Charles: I discussed this with Tabb today. He confirmed that my speculation was correct. Your best bet is to power the MoVI on with minimal acceleration and then keep it powered on. Not the most elegant solution to the problem, I grant you, but you're up against gravity and acceleration as I mentioned.

    Andy
     
  14. Charles Lim

    Charles Lim Member

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    ok i will give it a test these new ideas.
     
  15. Charles Lim

    Charles Lim Member

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    so when i reach the desired location for shooting . I tuned the rig back up to normal acceleration?
     
  16. Rob Drewett

    Rob Drewett Member

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    Hi Charles,

    I am glad you brought this up I also have a shoot in the North Sea filming trawler boats in a storm, if you have any advice it would be very much appreciated. Did you manage to waterproof the MoVI at all? I can imagine salt spray not being very useful for future proofing the rig!
     
  17. Charles Lim

    Charles Lim Member

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    will this work?
     
  18. Charles Lim

    Charles Lim Member

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  19. Rob Drewett

    Rob Drewett Member

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  20. Charles Lim

    Charles Lim Member

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    can freefly do some testing to see if this works?
     

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