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Electromagnet

Discussion in 'Electronics & Electrics' started by ][nfector, Nov 3, 2005.

  1. LethalCorpse

    LethalCorpse Member

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    so what? who cares if it's in a vcr or in a drawer full of dildos? the practical considerations remain the same

    Edit: oh, and he did mention the VCR. Read the thread or shut your mouth.
     
    Last edited: Nov 4, 2005
  2. Snakez001

    Snakez001 Member

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    Ummm... Explosives.. great..
    Did u ever read about how the fed's, NASA, and some recording media company (Iomega IIRC) reconstructed the shuttle tapes.. If they can do that from a tape thats been thru the worst kind'a re-entry, the VHS tapes are safe as..
    No to mention the world of bad that comes with explosives..

    I dont even want'a know what is on there that u need to destroy...

    Feds can recover an image on a VHS tape that has been recorded over 20 or more times, or erased 20 or more times..

    U could always just leave it outside. Background radiation, being a little stronger now that it was 100years ago, will destroy the data/image at about a rate of 10% per year in AU. The plastic tape, at about 1% per year.
    U will have to wait a while, but it will happen.. :)

    U can buy mass tape erasers, or just buy a de-gaussing wand..

    Explosives!? damn...
     
  3. Goth

    Goth Grumpy Member

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    Challenger never left the atmosphere... so the CVR's never had to survive re-entry. And as for Columbia, noone was ever going to recover videotape from what was left of that thing.
     
  4. DeNs

    DeNs Member

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    Hehe I just got a mental image of someone crawling into an MRI machine with a VCR when you said that.

    I was pretty confident when saying that, that a magnet like that alone would not be enough to destroy an entire videotape. Still, those magnets are fun to use.

    ---dens
     
    Last edited: Nov 5, 2005
  5. Crosspeen

    Crosspeen Member

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    Firstly, I dont know very much about electronics, so I might be WAY off the mark, but dont capacitors build up to a certain point before releasing all its charge at once?

    So maybe release a pulse big enough to do the job....?

    Just a thought.
     
  6. nux

    nux Member

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    Capacitors store charge.
     
  7. Bloar

    Bloar Member

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    Burn the tape and move 2 digital media which you can easily destroy liek a cdrom.

    ooo even better an excuse 2 buy a dvd video camera
     
  8. OsiC

    OsiC Member

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    The tape will not be effected by a magnetic field unless it has relitive motion to the magnet. This means you need to have:
    1) the magnet physicaly moving
    OR
    2) AC current, which pulses backwards and forwards 60 times a second

    An MRI machine wouldnt do anything. Althogh it has a ridiculasly strong electromagnet, unless you waving it around quickly the tape will not be effective. A MRI electomagnet doesnt pulse because it aligns atoms and keeps them uniform.

    So you need a soft iron core with an insulated wire wraped around it, with an AC charge going throgh it.


    edit:: read below
     
    Last edited: Nov 6, 2005
  9. Goth

    Goth Grumpy Member

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    What you need is a non-zero d/dt(B) at the tape surface, which is achievable by either moving the coil relative to the tape, or oscillating the current through the solenoid, you don't need both.
     
  10. OsiC

    OsiC Member

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    Yeah sorry I didnt put an "or" in there, ill fix it up
     
  11. OP
    OP
    ][nfector

    ][nfector Member

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    thanks to the guys who are offering helpful suggestions and actually reading my posts :thumbup:

    heres what I think I'll do:

    place an eletromagnet with a soft iron core somewhere near the read head right next to where the tape passes. When I want to erase the tape : switch an AC current through the electromagnet but also automatically engage the the fast rewind function in the process screwing the the previously recorded contents of the tape.

    Sound alright ?
     
  12. Myne_h

    Myne_h Member

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    On this topic, I have a few small dents in the roof of my car, I've often wondered if a bigass electro magnet might be enough to hold the metal to allow manual manipulation.

    Could it be done using a car battery and some of that winding wire they use on alternators, do you think or would it burn out? And most of all, is it possible to make it strong enough to re-shape sheet metal?
     
  13. Snakez001

    Snakez001 Member

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    Sounds good to me.. Use some glue to hold the rod in the wire..

    > Goth, the shuttle tapes are similar to home vcr's, helical heads etc. Readup on the Columbia. They recovered all 12mins of re-entry from just before the first oops, plus heaps more.. They physically rebuilt the tape after washing it etc, piece by piece, then reconstructed the data with a number of different techniques. All by hand..
    I still get weekly email updates on new findings etc..
     
  14. OP
    OP
    ][nfector

    ][nfector Member

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    no way. Your looking at something in the range of a 1/10 of a Tesla. You wouldnt even come close.

    To fix that u need one of those guns that welds a little pole onto the metal then u can pull the pole out with the metal to reshape. I forget what they're called.
     
    Last edited: Nov 6, 2005
  15. brokenback

    brokenback Member

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    “No that is exactly what the erase head is designed for, albeit at slower speeds. On a VCR the erase head is a small black head just prior to the rotating video head”.

    The video head has at minimum 2 heads. Each head is offset to each other by precisely 8 degrees (shit i cannot remember the exact offset, just guessing, I knew it once!).

    The heads write at an angle to the tape as they pass the write/read heads (the rotating heads. They write lots of fields at an angle to the tape, this is how they fit a movie on to a video) and this is how they PAL alternate the screens and fields. 1 field is one read head, the other is the offset head (the other field). 2 fields make a screen or 24 pfs interlaced.

    You have to remember the fields are at differing angles to each other also written at angles along the tape. To erase them is the job of the erase head.

    Trying to do this at a rapid rate is IMPOSSIBLE! As someone mentioned earlier, the effect of a degauss is the square of the distance. Thus degauss at the wrong angle or wrong angle and field = no degauss or data that can be re-compiled.

    It has been mentioned that degaussing at 60cps might work….no, this will only degauss the data at a 60 cps rate which can be integrated (re-compiled) back again, given the appropriate technology, aka the “feds”.

    You could degauss a video if you used a “white noise” generator (a generator that generates random harmonics across the spectrum used), but this would have to be very powerful considering the effect of the distance square rule (a basic physics fact).

    Just use a hammer or a burner!

    edit: why am i bothering?
     
    Last edited: Nov 6, 2005
  16. OP
    OP
    ][nfector

    ][nfector Member

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    despite your last post, i find it hard to believe that an oscillating and reasonably powerful electromagnetic field positioned within 1/2 cm of the exposed tape, wont alter the the tape enough to make it hard if not impossible to recognise the video on it.

    I'M NOT TRYING TO MAKE IT "FED" PROOF. Anyway, in Australia, considering the feds here are the Federal Police :o Why do people automatically assume im erasing something illegal.
     
  17. LethalCorpse

    LethalCorpse Member

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    people don't erase shit to make it neat and tidy. They do it to remove embarassing or incriminating evidence. So either it's videos of you rooting stuffed animals in your mum's clothes and you don't want her to see it, or it's videos of you rooting real animals in your mum's clothes and you don't want the feds to see it.
     
  18. #relativistic

    #relativistic Member

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    by non zero d/dt (B) do u mean a B field changing with time? or is that not a derivative ? :confused: :confused:
     
  19. Goth

    Goth Grumpy Member

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    Apologies for the blatant bump, but yes, that's exactly what i meant.
     
  20. tin

    tin Member

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    Or perhaps it's a security camera system that is watching something that losing the footage is better than getting it into the wrong hands. I can't think of why such a system would be using VHS, but who knows.
    I agree with the comment about everyone assuming it's something illegal or otherwise naughty.
     

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