I think they use Dire Straits, Sade and the Batman soundtrack.
November 22, 2015 5:53 AM   Subscribe

Start your day with a video and some ridiculous numbers: The Slow Mo Guys spin a CD at 23,000 RPM and film it at 170,000 FPS.
posted by AlonzoMosleyFBI (17 comments total) 14 users marked this as a favorite
That was pretty cool, loved how the failure spreads out from one point along the edge.

Also I learned that brits struggle a bit when they say "vacuum cleaner".
posted by octothorpe at 6:13 AM on November 22, 2015

We don't struggle to say vacuum cleaner, because we call it a hoover: I am going to hoover the front room.

This is ace, love the fractal style pattern the failure makes as it spreads through the disc. Also, the side view is amazing, and their comments about the warping are cool - it really does look strange.
posted by marienbad at 6:23 AM on November 22, 2015 [1 favorite]

Nature abhors a vacuum, so do Brits.
posted by blueberry at 6:24 AM on November 22, 2015 [7 favorites]

As a small aside, it really chaps my hide that these guys do this as a thing, and yet they don't own a 25 foot BNC cable and a pickle switch.
posted by ftm at 7:03 AM on November 22, 2015 [2 favorites]

It looks like the failure mode is a fracture at the edge of the disc caused by the flexing of that ripple resonance, which as they said moves at a different speed to the disk. I am not a fluid dynamicist, but presumably that's caused by airflow over the surface.

Be fun to repeat the exercise in (rather than with bits of) a vacuum, or at least in a much lower pressure atmosphere.

And jeez, I remember the excitement of owning an 8x CD-ROM drive. Let's see you read data off this one at top speed, lads...
posted by Devonian at 7:18 AM on November 22, 2015 [1 favorite]

I used to work near a real smart guy who had been in the disc manufacturing business for a long time.

He told me one time at lunch that the biggest problem with expanding to higher density/rpm/multiple layer disc media is that the whole industry is based on the one type of cheap plastic, and it can only structurally handle so much torque (angular rotation?(I'm bad at math)) .

We've been spinning it just below that for a couple decades now.
posted by Sphinx at 7:42 AM on November 22, 2015 [3 favorites]

I wonder how much friction at the disk/air interface has to do with the shattering. They should try a second set of videos with lubricated disks.
posted by oceanjesse at 7:43 AM on November 22, 2015

I'm kinda curious about how they pull 70Gb off the camera and store it somewhere, just in a few seconds.

Also, ultra-high-frequency gurning.
posted by benito.strauss at 7:50 AM on November 22, 2015 [1 favorite]

Technically, if they are spinning a CD that fast, they aren't actually playing that CD. CDs aren't vinyl -- they don't play faster if you spin them faster.
posted by hippybear at 8:28 AM on November 22, 2015 [1 favorite]

I'm kinda curious about how they pull 70Gb off the camera and store it somewhere, just in a few seconds.

The storage is on board. The camera records to high-speed internal RAM and then they play out from RAM by monitoring on the camera's HD-SDI output(s). The camera manufacturer also makes high-speed media that you can use to get the data off the camera relatively quickly (1 Gigapixel/second) so you can clear the on-board memory and keep shooting. You can offload the data via Ethernet, too.
posted by Mothlight at 8:41 AM on November 22, 2015 [1 favorite]

They mention that at its lowest resolution, the camera will do a million frames per second. I find that for most applications, I get acceptable results if I shoot five hundred thousand frames per second and then just play each frame twice...

...or, you know, shoot at 60 fps and then play each frame around sixteen thousand times. No, seriously, I'm sure there are perfectly good reasons why somebody might need to film something at a million frames per second, but it just sounds ludicrous to me...
posted by Sing Or Swim at 8:42 AM on November 22, 2015

No, seriously, I'm sure there are perfectly good reasons why somebody might need to film something at a million frames per second, but it just sounds ludicrous to me...

We sell cameras in this speed range for use in mechanical testing - two applications I can think of are Hopkinson bar testing, and pretty much anything to do with explosives - either protection from explosives, explosive metal forming, or explosive joints like the ones that let stages go on launch rockets. In the end, metal does pretty weird things when you pull it really fast. Cracks propagating in brittle materials would be another.

The resolution of the 2511 at 1 million frames is a little silly - 128x32 - but the state of the art is ~1 megapixel at 5 million frames from the Specialised Imaging Kirana which is a quarter million dollar camera and will usually be purchased by national labs or defense researchers. Making things worse pricewise, our particular technique requires a pair for 3D results.
posted by ftm at 8:50 AM on November 22, 2015 [19 favorites]

Cool. I'm now going to waste a lot of time on that channel.

It looks like the CD was warping in large part due to the motor mount itself being not quite centered. I wonder if it would do the same thing if you had a perfectly centered mount. Probably not.
posted by jimmythefish at 9:04 AM on November 22, 2015 [3 favorites]

Harold Edgerton would be proud.
posted by The Ardship of Cambry at 9:09 AM on November 22, 2015 [1 favorite]

oh hey, Slo-Mo Guys! We've been watching a bunch of them, plus a secondary Youtube channel "Smarter Every Day" that we found tangentially when the Slo-Mo Guys did a thing with the guy who runs SED.

Youtube specialty channels like these are the greatest thing to happen to TV recently. See also things like Roadkill (a couple of SoCal dudes faffing about with carbureted junkyard heaps, with a roughly equal distribution of breaking shit, breaking down, and burnouts), every current music video ever, and a bunch of weird fringe sports (like cyclocross) getting broader international coverage through their federation channels.
posted by lonefrontranger at 7:04 PM on November 22, 2015 [1 favorite]

here, this is the Slow Mo Guys episode that you didn't know you needed until now: 6 ft Man in 6 ft Giant Water Balloon.

it's utterly absurd, and my husband and I couldn't stop laughing at it.
posted by lonefrontranger at 7:17 PM on November 22, 2015

> CDs aren't vinyl -- they don't play faster if you spin them faster.

While they're not playing the CD, some CD players will actually time stretch a CD if you speed up or slow down the disc RPMs. This was pretty common for cheap portable disc players found in the mid to late 90s when cheap portable players became as ubiquitous as knock off tape decks were 10 years earlier.

Yeah, I know this presumes some pretty ridiculous things about the digital electronics in these devices, like having no true master clock control of the word/byte bitstream or perhaps treating the bits/bytes coming off the CD as the clock based on RPMs of the physical CD - which from an audiophile standpoint is all kinds of fucked up, but they existed.

I know about this because I was trying to find CD players I could manipulate by hand like vinyl turntables for cheap, portable DJing, because DJ rigs were still insanely expensive. ($1500 ish for a basic mixer and pair of Technics, headphones, monitors and PA not included). So I spent a lot of time picking up cheap used portable CD players, defeating the door safety switch and mucking about with my hands on spinning CDs.

Sure, trying to manually speed up CD wasn't ever really going to work. CDs spin much faster than vinyl. But on a larger number of portable players, slowing the CD down actually worked. Kind of. OK, so you would need to be a ninja robot to DJ this way with any accuracy.

Plus the sound was, oh, really gritty as the DAC struggled with dropped bits and frames and you could hear the granularity of the sample rate getting stretched the fuck out with no smoothing or interpolation.

Point being is that some CD players actually work just like an analog record, with less or more bits hitting the detector meaning slower or faster playback.

I never did find a player that would let me scratch a CD back and forth like batman in that really bad movie. Reversing the bitstream always made the DACs just stop playing audio. There was a limit to how much you could slow down the CD before the DAC just gave up entirely, and then it wouldn't start working again usually until the CD was back to normal RPMs and it grabbed a good few bytes, at which point you could start stretching it around again.
posted by loquacious at 8:00 PM on November 22, 2015 [5 favorites]

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