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13790Re: [GPSL] Freee Fall Camera

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  • James Ewen
    Feb 12, 2014
      On Wed, Feb 12, 2014 at 6:16 PM, Pete Lilja <plilja@...> wrote:

      > GoPros aren't particularly heavy and are well protected I their case. I
      > wouldn't hazard a guess on the rpm rate.

      Depending upon the mode the camera was in, the frame rate could be up
      to 100 frames per second, but more likely 60 or 30 fps. Listening to
      the audio, it sounds like it's pretty close to 60 Hz. Play the video
      audio along with a tone generator and match the heterodyning.

      Load up the video, and go to this website
      http://onlinetonegenerator.com/ Set the tone generator for 59.8 Hz.
      Start the tone generator and play the video from about 0:30 until
      impact. You can hear the heterodyne start to synchronize as the speed
      of rotation picks up. By the time of impact, the troughs and valleys
      in the mixing audio just about synchronize. Wearing a headset or
      earphones helps with hearing the heterodyning.

      > James - you're the first person to comment on his using the grass rather
      > than the asphalt. He does it to reduce wear on the tundra tires ( which,
      > interestingly, are inflated to only 4 psi!)

      I figured he had tundra tires on the aircraft... They work well for
      landing on gravel bars!

      > Maybe something is lost in the video. The approach angles seem very
      > comfortable. Speeds are very slow in that plane.

      The fish-eye distortion of the camera probably makes the approach
      angle look lower than it is.

      > On Wednesday, February 12, 2014, Joe <nss@...> wrote:
      >>
      >> It is a camera in free fall from a very high altitude 10K+ probably

      Judging by the visual references from the aircraft, and skydiving
      experience, I guessed somewhere just over 3000 AGL. 3000 to 3500 feet
      above ground is the usual place to throw students out of the plane.

      If you do the math, where d = 1/2*g*t^2, with g being gravitational
      acceleration, and t being 27 seconds between drop and splat, that
      works out to 3572.1. That's pretty close to my eyeball estimate, and
      I'm happy with saying somewhere around 3500 AGL.

      >> Like i said forst time I wonder what the G forces were at impact and what
      >> rpm it got to to synk the video like that?

      The G forces weren't as high as they could have been. The pig pen was
      soft mud rather than rock or concrete, so there's a bit of squish
      factor. The high spin rate would also make the camera roll,
      distributing the impact slightly. I'd like a much higher frame rate to
      be able to get time of impact and time of cessation of the initial
      impact to be able to calculate the actual G forces sustained. You can
      see the bounce and roll in the video. As I stated to another on
      Facebook yesterday, I'd suspect there was more force exerted on the
      case by the pig's jaws than the impact.

      BTW, if you fall out of a plane and land in a pig pen, you have about
      14 seconds before you become lunch... get up and run!

      The camera was recovered 8 months after it fell. It sounds like the
      camera lay in the pig pen for 8 months according to the guy that found
      the camera in his pig pen. That's more a testament to camera
      durability than falling 3500 feet!

      It's all about physics and math... those things that kids say they
      will never use after graduating high school. Thank you to all my
      instructors for giving me a sound basis from which to derive many
      thousands of hours of future enjoyment. Without that education I'd be
      sitting on my couch wondering things like "How high is that plane
      flying?", "How fast is that camera tumbling?", or a plethora of other
      easily deduced or calculated facts.

      --
      James
      VE6SRV
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