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Syncing frame rate to chopper rotation

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Syncing frame rate to chopper rotation

Postby Steve Grisetti » Wed May 22, 2019 6:51 am

Here's a pretty cool video.

The photographer matched the frame rate of the video to the speed of the helicopter blades -- so it appears the copter takes off and flies away without turning on its motor!



At least I hope this is real. There are some aspects of it that seem a bit suspicious to me. (Like the fact that the blade speed wouldn't remain consistent the whole flight. Would it?)
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Re: Syncing frame rate to chopper rotation

Postby Dave McElderry » Wed May 22, 2019 9:02 am

Pretty cool. Right at the beginning the blades have a slight turning motion, and in the last few seconds there's definite motion, so this may be legit.
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Re: Syncing frame rate to chopper rotation

Postby sidd finch » Thu May 23, 2019 10:07 am

That looks pretty cool. I wonder how you sync the frame rate. but a pretty cool effect.

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Re: Syncing frame rate to chopper rotation

Postby Bob » Thu May 23, 2019 5:04 pm

Dave McElderry wrote:Pretty cool. Right at the beginning the blades have a slight turning motion, and in the last few seconds there's definite motion, so this may be legit.


It is legit. Most helicopters are designed to operate within a narrow rotational speed range. In normal flight, it usually stays within plus or minus 1% which is vary nearly constant. The rotational rate is related to the size of the rotor. They want the tip of the rotor blade to remain subsonic, so, the longer the blade the slower the rotation. Since most video cameras have fixed frame rates, I would assume that this helicopter has a rotational rate which is an integral multiple of the frame rate. Say 300 rpm and 30 fps. It also looks like the shutter angle (shutter speed) was adjusted to eliminate motion blur of the blades.
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