Shooting from a train. iPhone starts to roll?

Discussion in 'Movi Technical' started by John Chu, Jun 13, 2018.

  1. John Chu

    John Chu Active Member

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    I first encountered this issue a while back and decided to try recording while riding the subway with the normal custom tune for my iPhone 6s.

    I'm facing and aiming the phone out the window. I'm perpendicular to the direction of travel. As the subway train accelerates, the phone starts to roll and tilt to the direction of travel, so the horizon is no longer level.

    I tried using the both the custom tune, and the "regular" tune setting and I tried to quickly test increasing the roll stiffness. Any hints on why this is happening or fix this issue? This seems like something a stabilizer should have no issue handling.

    Here is a video example:
     
    #1 John Chu, Jun 13, 2018
    Last edited: Jun 14, 2018
  2. Rorick Edge

    Rorick Edge Active Member

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    Presumably it only does this when the train is accelerating or decelerating. If so, the forces are fairly strong. The human body has the same reaction.
     
    #2 Rorick Edge, Jun 13, 2018
    Last edited: Jun 13, 2018
  3. John Chu

    John Chu Active Member

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    It just starts to slowly roll while the train is in motion.
     
  4. Rorick Edge

    Rorick Edge Active Member

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    But does it do that when the train is at a constant speed? Try this somewhere that there’s a long stretch between stations, e.g. on the 7 express train. I’m willing to wager that this will only happen during acceleration and deceleration.

    Have you tried locking roll?
     
  5. John Chu

    John Chu Active Member

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    It never corrects itself. But I usually stop recording once the rolling begins. That Freefly Movi intro film has a guy on a hoverboard and he was able to do it.. and walking is generally okay. If it needs a super locked down mode for these types of situations it’d be helpful.
     
  6. Rorick Edge

    Rorick Edge Active Member

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    I’m going to try to replicate this sometime this week on the 7 express. I suspect that it’s acceleration and deceleration forces. If so, it might well be necessary, or at least a good idea, to level the phone once the train achieves constant speed. If it rolls at constant speed, that is truly odd, to the point of not making sense. I’d also like to think that locking roll might fix this, but acceleration/deceleration forces are quite strong.

    I doubt that people on hover boards, especially with a Movi in hand, are accelerating and decelerating at the rate of a NY subway train, at least not if they want to stay on the board :)
     
    #6 Rorick Edge, Jun 13, 2018
    Last edited: Jun 13, 2018
  7. Rorick Edge

    Rorick Edge Active Member

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    I just looked at the Movi intro film. The hover board clip, which is at about 01:04, is two seconds long and the guy is moving at a constant speed :)

     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    John: Congratulations! <grin> You have just demonstrated that Einstein is correct -- acceleration and gravity are indiscernible -- so when you accelerate it's just like gravity -- and horizontal acceleration/deceleration thus shifts the direction of Earth's gravity (normally vertical) off to one side when you combine the Earth's gravity with the horizontal acceleration. (Technically the horizontal acceleration vector and the gravity vector combine to produce a resulting vector that is not vertical.)

    EDIT: Oh...I forgot to mention that when you move at constant velocity you are neither accelerating nor decelerating, that's why the tilt/roll no longer happen.

    I'm afraid you'll need to appeal to higher powers than Freefly to change things! :)

    Cheers
    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. John Chu

    John Chu Active Member

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    On a mechanical Steadicam, a sudden jerky movement can cause a pendulum type swing, so the operator can slightly feather and" brake" the rig and keep it from swinging. (Of course adjust top and bottom heaviness as needed.)

    I don't think the train movement is that demanding or excessive.

    The gimbal motors should be able to keep the unit level in my opinion. But I have no idea... is this too demanding a situation for gimbal stabilizer? (Filming in the the same direction of travel or facing towards the rear of the train should be fine.)

    I look forward to Rorick's test.
     
    #9 John Chu, Jun 13, 2018
    Last edited: Jun 13, 2018
  10. Rorick Edge

    Rorick Edge Active Member

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    Hi John,

    I’m making a short film about one of the NY subway lines, so I’m interested in this and will indeed be doing a test on the 7, E or F train, whichever gives me a good distance between stations when I can do this.

    I’m not surprised that the Movi is susceptible to these forces, but I’d appreciate knowing, assuming that you were using the Movi app, whether you had roll lock on.

    Also, have you taken footage like this on elevated tracks during the day and, if so, how big a problem was rolling shutter with your iPhone 6S?

    Thanks
     
    #10 Rorick Edge, Jun 13, 2018
    Last edited: Jun 13, 2018
  11. John Chu

    John Chu Active Member

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    Yep, I never unlock the ROLL in anything. I always want the the horizons level when possible.

    I expect the rolling shutter on the 6s to be as bad my previous iPhone 6. It never really bothers me, except the jello-distortion effect if the phone is jarred violently from my bad foot work.
     
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  12. Steve Huether

    Steve Huether Member

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    I've been curious about this since I had my Osmo+. I had it mounted to the window of my truck and noticed that when turning corners, accelerating, or braking (anything that introduced acceleration on the gimbal) that the gimbal would wander and then slowly return to normal once the acceleration ended. I have a feeling it has to do with how the electronic gyro sensors work. I'm planing to test with the Movi CR mounted in my truck for a hyper lapse on the way home so we'll see...
     
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  13. John Chu

    John Chu Active Member

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    Thanks for that information! I guess this is a limitation of gyro stabilizers when shooting laterally to the direction of travel. I just assumed that the gyro motors would do their magic and resist and negate that initial jolt of acceleration.

    Upon looking at some of the old footage, once the train is at speed, it seems to be okay.

    I may try lightly assist the phone by pinching the top and bottom edge of the the phone during acceleration the next time I try to record.
     
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  14. Steve Huether

    Steve Huether Member

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    Thinking about this further, and I'll test later, I wonder if Freeze mode would help at all? Or maybe Tripod mode?
     
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  15. John Chu

    John Chu Active Member

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    Ha! I think you are right!

    I just changed the trigger to activate FREEZE instead of the (useless to me) ROLL mode. The freeze function looks like it is going to be perfect when I'm trying to do my lateral moves too.

    Steve you are a GENIUS.



    I was never happy trying to do a lateral move down the street, and the horizon would kind of tilt. This mode looks like it should work perfectly.
     
    #15 John Chu, Jun 14, 2018
    Last edited: Jun 14, 2018
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  16. Rorick Edge

    Rorick Edge Active Member

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    For iPhones with optical stabilisation, especially if you’re seated in something like a subway car, it’s probably worth testing what happens when you shoot with the phone without using a Movi. If there’s some movement, it may actually look good.
     
    #16 Rorick Edge, Jun 14, 2018
    Last edited: Jun 14, 2018
  17. Steve Huether

    Steve Huether Member

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    Well I wound't go THAT far but glad to help! The Osmo+ used the trigger in a Freeze mode and I found it very helpful in some situations. :)
     
  18. Steve Huether

    Steve Huether Member

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    True. Sometimes slight movement of camera gives a more natural feeling to the video.
     
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  19. John Chu

    John Chu Active Member

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    I'm so "annoyed" that the freeze mode wasn't featured more prominently in the tutorials.

    Freeze mode makes walking forward in a straight line so much easier.

    I was constantly trying to expand the window plus selecting slower speed and I still couldn't get the unit to not wander while walking. (Like a car with vague steering or overly sensitive steering and having to correct to center.)

    It is a rant, but the joys of feature discovery isn't my bag ----- like the hidden features in iOS on the iPhone. :)
     
    #19 John Chu, Jun 14, 2018
    Last edited: Jun 14, 2018
  20. Steve Huether

    Steve Huether Member

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    Lol I hear you. Coming from the Osmo I've had to get used to not being able to set the "normal forward" position on the fly. The Movi in most modes seems to always default to straight ahead in relation to handle. This work well for hand held but when mounting it to something else, it presents a challenge of making sure its mounted to have that default view work.
     

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