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How do discs spin in drives?

Discussion in 'DVD / Blu-ray drives' started by pkrillo, Apr 28, 2011.

  1. pkrillo

    pkrillo Member

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    I was thinking about this the other day. When I place a blu-ray disc into my PS3, about halfway through it "sucks/draws" it in automatically (like when you put a CD into the disc changer in your car). What exactly is the "force" that pulls it in? Is it some sort of mechanical tool, and can it damage your discs?

    Also, I have always been confused as to exactly HOW discs spin inside the drives. I know some drives, you "lock" the disc in (the small, round thing in the middle that locks the disc in also spins it). However, in others, a tray ejects and you place the disc onto the tray. Well, the disc goes in, and you cannot see what happens to it from that point on ...

    How do discs spin in those kinds of drives? And how are they "locked in?" I mean, don't they have to be "locked" in order to spin without wobbling? But if you simply place it onto a tray, how can the drive "lock" the disc in and spin it automatically? I just wish I could see it happening inside the drive for myself ...

    I'm always afraid my blu-ray discs will get damaged somehow (not scratches, but CRACKS) inside the PS3, because I always leave them inside the console after I finish playing (I usually spend 2-3 weeks on a game, so it would not be practical to eject the game every day). Once you "send" the disc into the PS3, there's no telling what is happening to it on the inside.

    Thanks!
     
  2. DXR88

    DXR88 Regular member

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    the disk gremlins pull in your game on the PS3 (its not the truth but hey its pretty mysterious right!) the truth is its operated by two pulleys on the drive, which grabs it and pulls it in. this type of drive is more prone to jamming and wearing out, but its based around a very compact design the size of the that slot is about the same size as the drive Vertically.

    on Desktop drives that tray that shoots out is operated by a set of cogs and gears...on cheaper drives its operated by a rubber band literally, sorta works like a timing belt would on your car.

    the laser movement is controlled either magnetically or by a worm gear. a worm gear is a metal rod with a set of machined groves etched in it, magnet drives are brand new tech altogether still in infancy if yet even born to the consumer world yet.

    the rest is operated pretty much the same when a disk is loaded or the tray is closed the laser assembly moves up Locking the tray into position(its the reason why you just cant yank open the tray) Wobble is controlled by hydraulics in the drive motor, and by a magnet which can be found on the top of the drive casing. this creates enough pressure on the disk to keep it from wobbling.

    the inner workings of optical drives are very intricate. the slightest miscalculation on any part of the drives mechanics can literally cause the whole thing to fail.
     
  3. pkrillo

    pkrillo Member

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    Thank you for that answer.

    So then when the player/console/drive is switched OFF, but the disc is left inside, is the disc "locked" or can it move freely? In other words, if one were to hypothetically knock off or shake the device (when turned OFF) while the disc was inside, would it be "locked in" like when it is suspended in its case, or would it "bump around" inside there?

    I realize that doing so when the device is on and the disc is spinning would be bad, but what if the device is OFF?

    Also, why is it that CDs don't get scratched in a disc changer inside your car? It seems like a strong, outside force (while the disc is being played) could disrupt the inner-workings of the drive, but why is it that CDs can survive all the braking, speed bumps, etc. of driving without a scratch (no pun intended)?
     
    Last edited: May 1, 2011
  4. DXR88

    DXR88 Regular member

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    if the tray is closed, its locked. if the tray is open its unlocked.

    if you power it down with the disc inside its locked, but there might be a slight wobble simply because in a powered off state the drive Motor has no resistance. as with all things nothing escapes the tug of gravity.

    if your going to moving the console. make sure you remove the game, otherwise you risk damage to the drive even if that risk is very low. better safe than sorry

    because there sandwiched in between the drive tray and a magnet. there is no vertical movement room, but not enough pressure to damage the disk.
     
    Last edited: May 1, 2011
  5. xboxdvl2

    xboxdvl2 Regular member

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    old car cd players use to skip.i know someone who accidently drove of a small cliff and the cd was jumping while the car was on the ground upsidedown.old cd players use to jump i remember my sisters sterio when i was a teenager she played a song i hated(at a high volume).i started jumping up and down outside her bedroom and the cd was skpping badly.the ps1 lasers are driven by cogs and gears.take an old cd player apart and you will see how it works best way to learn.
     
  6. NteStlKr

    NteStlKr Member

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    disc drives today (in cars) read ahead, and store the information in memory. The lasers still skip and have read errors over bumps, but as long as the memory the player has outlasts the vibration/bumps, you won't hear it.

    and to add a little info to the locking discussion, there are generally two magnets (or one magnet and a ferrous metal piece). One magnet is in the drive motor, and the other magnet (or ferrous metal piece)is on the other side of the disc. Whenever the laser assembly moves 'up,' the magnets sandwich the disc in, keeping the plane of the disc parallel to the plane of the top of the drive motor (and, thus, the laser rail). I've never seen hydraulics in drives, though I suppose it is possible. All the drives I've seen have little rubber pieces that act as shock absorbers.

    and regarding damage due to movement... it is always best to remove media during transportation of any kind. Leaving it in over night is fine, and produces much less wear and tear than taking it out at night. I don't know why anyone would think otherwise... but anyway, when a drive is on (disc is spinning) any damage to the drive and disc will be far greater (as the energy of the spin of the disc will be added to any other forces acting on it). Also, when spinning, momentum keeps the disc wanting to spin on one plane. So, if the drive (or console) is tilted or moved, the disc will want to stay at the original plane (until enough energy is added to change planes). (in other words, it acts like a gyroscope) This means that there is a very high chance of the disc scratching against parts inside the drive. So never move anything with a disc in it until it is off, and has stopped spinning completely! This goes for anything that spins, or has a spinning component; optical drives, hard drives, fans, drills, and so forth.
     

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