PowerLabs High Speed CD-Rom Experiments

Introduction:

 Setup:

 Before an experiment could be devised where a CD would be rotated to complete failure, a proper motor had to be obtained that would be capable of achieving those high rotational velocities with the load presented by a CD. Although a CD is very light and aerodynamic, when it starts to spin at a couple tens of thousandths of rotations per minute the drag created by air around its surface can be sufficient to slow the motor down considerably. High torque motors are very common and cheap, as are small high speed motors. Unfortunately however, high speed, high torque motors are a much rarer and expensive find.
 My choice was to use a Dremel tool as the motor. It was cheap, easily available, and, more importantly, the rated 35000RPM spindle speed meant that it had some real potential for spinning things to destruction.

 At 35000RPM very small imperfections and balancing errors can lead to extreme vibration; so much, in fact, that it would be possible to damage the bearings or bend the axle on the tool if something as heavy as a CD was to start wobbling (bear in mind that the Dremel tool was designed for very small, light weight loads and even then many of its attachments carry warnings not to be used at full speed). One of the first challenges of the research was to find a means to secure the CD perfectly in the middle of the tool. A custom made CNC lathe spun aluminum holder was considered but before I ever left the room I realized that the cylindrical sanding attachments Dremel makes not only fit a CD hole perfectly, but also have adjustable width so that the CD could be gripped in place.
 With the CD in place and the dremel plugged in, it was time for the fun to begin!

 The Dremel was switched on and the rotational velocity was gradually increased to its maximum, at which point the CD hummed and whined in a very menacing manner. Mildly disappointed that it had not exploded, I realized that it wanted out; a quick jerk at the tool and the CD slid out of the holder and contacted the carpet whilst spinning at ungodly speeds. It peeled out a bit in front of me and proceeded to make its way to the door at a very high speed. On contacting the closed door, the CD did a most unexpected thing: it first bounced back a few inches, and then, when it hit the door again, it jumped straight up the door and struck the ceiling, exploding into thousands of fragments which rained down on the entire room. This first experiment was unfortunately not videoed, but it served to get everyone in the room to put glasses on and cower away behind pieces of furniture, whilst people in the hall corridor quickly made their way to my door to ask what was going on. Now, with an audience, the camera was taken out and the real experimentation began...
 A standard compact disk has a diameter of 12cm. If this disk is to spin at 35000RPM, the peripheral velocity at the edges of the disk (.377m circumference x 583.3 turns per second) will near 220m/s, or 722fps, or 792km/h or 492miles per hour. That is one fast CD-Rom!

 At those speeds the CD is storing over 150joules of energy.

Conversely, if the CD was to explode at that velocity, the pieces would escape at a similar speed. Although a Dremel tool does not have the required power to sustain its maximum RPM with a load as big as a CD-Rom, the CDs did go very fast; fast enough to blow all the foil off from one of them, explode another, and launch several across the room at speeds high enough that they exploded on impact, or flew up to the ceiling. Videos are available below for your amusement.

 Results and Discussion:

Click picture to watch the full CD experiment video (1m28, 8mb), or check out the best exploding CD here. (6s 2.1mb)
 No one of harmed by the experiments, of course, thanks to the fact that on fragmentation, rotating objects break away at a direction perpendicular to their axis of rotation meaning that the entire room was peppered around the CD, but nothing behind or in front of its face could get hit.
 Several companies have made the maximum speed CD-Writing standard 48x (see article) instead of 52X or higher due to the fact that at 52x the CD is spinning at 10 000RPM and several CDs have been known to explode at those speeds, destroying the drive and some times sending pieces out from the CD tray. The fastest drivers on the market today employ multiple reading heads to achieve twice, or even 3 times the read rate for the same RPM, so until DVDs take over CD drives still have a lot of room for improvements. Just in case anyone is wondering: if a CD really was to spin at 35000RPM in the drive, it would be possible to read it at 175X :)
Update: Matt e-mailed me the following warning:

You'd think a CD could handle 52x, right? After all, they make drives that fast.... but apparently that's not in the Playstation black-disc spec. I tried playing GranTurismo on ePSXe, and it exploded right in the drive!
Shockingly, we all got hit with shards of CD (which were slowed down when they blew the faceplate off my CDROM drive), but the computer was fine, and the CDROM still works today, after dismantling it and removing all the shattered plastic.

- Matt Pierce

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Hits since 06/06/2003.
Last updated 11/02/10

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