Adding strobe hashes to Presto platter

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rsimms3
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Adding strobe hashes to Presto platter

Post: # 46381Unread post rsimms3
Fri Mar 10, 2017 8:49 pm

I've wanted to do this for a while, especially after I saw a 6N of Mike Dixon's that had strobe hashes on it. I've researched and did some math but it's not quite cooperating. I think part of the issue is the process in the development of my strobe strip but wanted to get some feedback.

First, measured the circumference of the platter with a strip of paper snug on the outside, measured very close to 53.4375 inches. Doing the math using radius which seems to be right at 8.5 inches with a diameter of 17 inches.

So, for 33.3 rpm it's calculated at 216 hashes or 1 hash every .24739" or .24724" depending on which circumference measure I use. I set up Photoshop to create grid with spacing at .24739 and start adding equidistant hashes of the same width. When I print, tape together, and apply the band just snug I get 217 equidistant hashes. If I use .24724" I can get 216 but I have to apply the band very snug and it still doesn't run quite in time.

Thoughts? Suggestions? Using the wrong approach or equation? I think I need to increase the resolution in Photoshop when creating/printing my hash band to get higher level of accuracy.

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markrob
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Re: Adding strobe hashes to Presto platter

Post: # 46382Unread post markrob
Fri Mar 10, 2017 9:52 pm

Hi,

One issue you might be running into is that most printers are not super accurate (maybe +/- 1%??). Sometimes they scale different in the X direction vs. the Y. You may need to use the math to get close and cut and try to get it to work out right.

Mark

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grooveguy
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Re: Adding strobe hashes to Presto platter

Post: # 46463Unread post grooveguy
Tue Mar 21, 2017 11:25 pm

Mark's right about printers. First do a strobe disc, where "size doesn't matter" and see if it stands still. Your math is spot-on if you'll be viewing with a neon, an iron-ballast fluorescent or just an incandescent bulb that flashes 120 times per second. Put a diode in series with your neon or an LED and you'd need only 108 segments for 60 flashes per second.

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2bitcomputer
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Re: Adding strobe hashes to Presto platter

Post: # 46464Unread post 2bitcomputer
Wed Mar 22, 2017 2:49 am

How about using equidistant hash marks, say 8 or 16, and building a custom strobe that flashes at 100hz (3 x 33.33333).
The strobe could just be a Teensy 3.2 driving an LED using the 'analogWriteFrequency' function?

https://www.pjrc.com/teensy/td_pulse.html

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2bitcomputer
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Re: Adding strobe hashes to Presto platter

Post: # 46465Unread post 2bitcomputer
Wed Mar 22, 2017 4:55 am

That's definitely not going to work because the math is wrong.
33.33333333 rpm/60 = .55555555. hz which would be the frequency the strobe would need to flash at to freeze the TT once per revolution.
If there were say 180 hash marks on the TT the strobe could flash at 100hz (180 x .55555555 = 100) and the hash marks would appear to be frozen if the TT was spinning at 33 1/3 rpms .
So wait...was I (accidentally) right about 100hz but wrong about the number of hash marks?
180 hash marks would mean 1 hashmark every 2 degrees or could you do one every 4 or 8 degrees and have it work...

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