Forum: Catapult Message Board

> I posted 2 videos on youtube but neither did a good job of showing the spin imparted by the sling pouch but I am obviously not a cinematographer by trade. I am using grapefruit with a black line spray painted on them and I thought I was loading them correctly in the sling but I think the problem might be either with the focus or something I am not thinking of. Any suggestions as to how to better mark the fruit or get a shot we need to prove the naysayers wrong?
>
> http://www.youtube.com/watch?v=lXXam3vCRl4
> http://www.youtube.com/watch?v=CtZyozmqR28
>
> The videos on the computer as easier to view but I figured I'd give you an idea of what I was going for and then get better suggestions.

Trebdude,

In my opinion the only way you are going to be able to show sling in the video is if you have a camera that has at least some sort of high speed function and film the shot at a right angle to the throwing direction. IE throw north but have the camera pointing either east or west. you will probably want to have the frame of the shot set up very similar to what you had. With this shot the projectile will be in the shot less but at least the camera will be in focus at the projectile.

Or you could try it in a fashion that i think will work. The rest of this post will be assuming that this works. What you would have to do is come up with a projectile with one hole in it that you can hear whistleing in the video clip. If there is enough spin and the hole is in the right position on the ball as it is spinning you should hear the pitch of the whistle rising and falling. This would be due to the "Doppler Effect". Once you have a video clip of the shot with clear audio of the whistle you should be able to seperate the audio from the clip with a program such as AoA Audio Extractor with is a free program found on the web. With the audio seperate you should be able to convert that sound to a .wav file and be able to "see" the sound wave and from there its just simple math after counting the rises and falls in the pitch.

Mel

Hey, how about you place the camera just past the point of impact, pointed back toward the treb. That way the grapefruit will get bigger instead of smaller as the video progresses.

Thomas

I like the spinning whistler idea. Just to throw out a slightly wacky idea though...

Wrap the Payload with a ribbon. Not all around it but along a great circle route. Use enough to make several layers. Shucks, you might even make a groove in the Payload for the ribbon to sit in, to keep it in place while all else is going on.

Set the Payload for launching such that as the Payload spins the ribbon can unwind from it. This may take a few trial efforts.

Now film the action. Your looking for when the ribbon is fully extended, unwrapped. After that, we don't care what it does. Knowing how long the ribbon is and how long it takes for it to unwind should give you the rpm rate.

Hey, I said it was wacky, didn't I?

Any suggestions as to how to better mark the fruit or get a shot we need to prove the naysayers wrong?

Ignore them.
They are wrong and we don't need to prove it, they need to prove themselves right to us.

A while back, Butch Thompson made a neat little video called "Treb 4" in which he threw bowling balls. The warbling whistle clearly demonstrated rotation in flight and the night time shots with the magnisium fireballs showed it once and for all that normal, over-the-top slinging results in some back spin.

Ergo, we have science on our side and we don't have to prove nuthin', honey.

I wonder if air passing over the nose holes of a severed head also make that whistling sound.
Where are those naysayers when you need 'em.

If rigor has set, possibly.
If not, then I suspect that the breeze would close the nostrils enough to prevent whistling. After all, it isn't the wind going into the holes, but rather across them that produces the sound.

Mustache muffler?