Author Topic: Dave's Cup Tape Illusion  (Read 6539 times)

fzzyrn

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Dave's Cup Tape Illusion
« on: May 24, 2008, 12:54:44 pm »
We've all seen Dave's VOTW with his awesome cuptape. What i would like to know is that if this effect is possible on the naked eye without being viewed through a camera. I sat down and did some very questionable math about this.

After doing a bunch of research, the "refresh rate" of the human eye seems to be somewhere between 25-60hz. Using the inverse rule, this equals a period of 1/25 sec to 1/60 sec. Any particular point on the diab has to pass your eye 25 to 60 times per second. This would equal to 25-60 rps (rotations per second). Multiply that by 60 to get the RPM, you get an rpm that ranges from 1500 to 3600rpm.

The Nyquist frequency is the frequency at which aliasing ceases. This is equal to 2 times the bandwidth. In this case, the Nyquist frequency for the human eye ranges from 50 to 120 Hz. My theory is that up until the Nyquist frequency, the diab's motion gets progressively more aliased, then becomes a blur.

Now this is some VERY questionable math and physics, so feel more than free to correct me, but i want to know how Dave gets his tape to sparkle

JimmyCords.

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Re: Dave's Cup Tape Illusion
« Reply #1 on: May 24, 2008, 01:26:21 pm »
Yea, your maths seems to be right. Im going to try this. But one thing I should point out, Dave has more than one piece of tape on. I cant really see, but i think hes got 4 peices, this means that to get your diabolo to appear stationary whiles it spinning you only need to have it spinning at 375 - 750 RPM. I 'spose using this you would be able to get a rough estimate as to how fast u can get your diabolo to spin.
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mellowscholar

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Re: Dave's Cup Tape Illusion
« Reply #2 on: May 24, 2008, 01:28:51 pm »
I was thinking about the "wagon-wheel" effect on Dave's videos, is that what you mean?

EDIT: I thought there were only two, like in one line across the cup. The diabolo will appear stationary when it's spin frequency (rps) equals the frame rate of the camera.

dave from the grave

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Re: Dave's Cup Tape Illusion
« Reply #3 on: May 24, 2008, 02:04:49 pm »
Beware of the super secret guild of shadow spooners!

fzzyrn

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Re: Dave's Cup Tape Illusion
« Reply #4 on: May 24, 2008, 02:08:17 pm »
Shiny! Me likes...
I can't believe my math was even somewhat correct.
I'm so gonna do this to my finesses, i just need to get the tape.

dave from the grave

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Beware of the super secret guild of shadow spooners!

mellowscholar

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Re: Dave's Cup Tape Illusion
« Reply #6 on: May 24, 2008, 02:43:37 pm »
i have 2 stripes!
i knew it!!

does the effect happen when you look at it, ie not on camera?

dave from the grave

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Re: Dave's Cup Tape Illusion
« Reply #7 on: May 24, 2008, 02:51:12 pm »
no your eyes are far Superior to any reasonable camera you can buy. plus i think the diabolo would need to spin at an astronomical rate to create the wagon wheel effect on an object so small.
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Eric Moffett

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Re: Dave's Cup Tape Illusion
« Reply #8 on: May 24, 2008, 04:55:28 pm »
Well, I don't think size is a factor, a car going 45 - 60 mph can wagon wheel effect to the naked eye easily... as soon as I'm in my moms car again i'll figure out the approx rpms

there is also http://www.identi-tape.com/index.html which has an amazing selection of all sorts of metallic prismatic etc tapes in different widths and lengths... never bought from them but they look good.
Diabolo Acquired - Thurday, 2/08/07
Vertax Skill Acquired - Thursday, 4/12/07
2 Diabolo Skill Acquired - Tuesday, 5/29/07
3 Diabolo Skill Acquired - Eh, No?

MikeW

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Re: Dave's Cup Tape Illusion
« Reply #9 on: May 24, 2008, 05:06:20 pm »
is it sad that when reading this thread all im thinking about is my Integrated Circuits class i took last semester?
I do what no one else does today so that i can live like no one else can tomorrow.

mellowscholar

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Re: Dave's Cup Tape Illusion
« Reply #10 on: May 24, 2008, 05:09:32 pm »
I think the effect can be more or less apparent on a car depending on the hubs. I agree with dave on the size thing.

dave from the grave

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Re: Dave's Cup Tape Illusion
« Reply #11 on: May 24, 2008, 05:15:16 pm »
size is a factor you see a wagon wheel will create the effect at a far lower speed than a car wheel. the small the diameter of the object spinning the faster it has to spin to create the effect.

 hold on i might be wrong actually u see the wagon wheel effect happens on a circular object spins faster than the (frame rate) of your eye. now the spokes on a wheel have less of an interval between them at the center of the wheel rather than the edge. do if you widen the spokes you have to spin them faster to make the effect happen. thus if you put one stripe on one side then the effect should be achievable.

if that doesn't make sense then shoot me.

I'm going to try it now.

i tried it and span a diabolo to as fast as i can possibly spin it and i still couldn't out pace my eyes.
Beware of the super secret guild of shadow spooners!

Eric Moffett

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Re: Dave's Cup Tape Illusion
« Reply #12 on: May 24, 2008, 05:22:26 pm »
then we should get a bigger diabolo? Performer anyone?
Diabolo Acquired - Thurday, 2/08/07
Vertax Skill Acquired - Thursday, 4/12/07
2 Diabolo Skill Acquired - Tuesday, 5/29/07
3 Diabolo Skill Acquired - Eh, No?

CheshireBeagle

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Re: Dave's Cup Tape Illusion
« Reply #13 on: May 25, 2008, 04:02:25 am »
The obvious solution to this problem is to replace your eyes with cameras via surgery, duh.
-Beagle
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Shaun

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Re: Dave's Cup Tape Illusion
« Reply #14 on: May 25, 2008, 05:45:48 am »
...don't be silly, get in jiggy wid it.
It looks good, but...too much effort for bling, won't the tape just fall of after a couple of weeks? I'd rather something more permanent.

dave from the grave

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Re: Dave's Cup Tape Illusion
« Reply #15 on: May 25, 2008, 09:54:11 am »
ive had that in for at least 6 weeks i think and its stayed in fine. and i dont go easy on my diabolos mind!

im booked in for monday to have my eyes replaced. cost me a total of 5 pounds and a small puppy.  :D
Beware of the super secret guild of shadow spooners!