## 13790Re: [GPSL] Freee Fall Camera

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• 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
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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