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Read write heads with arm — Parallax Forums

Read write heads with arm

gambrinogambrino Posts: 28
edited 2009-06-08 21:18 in Propeller 1
Hello Forum , i would like to ask you about the HD arm in the hard disk drive , does anyone connected this motor to the Propeller ?Or how i can run this motor throught Propeller.
Thank you in advance,
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Comments

  • LeonLeon Posts: 7,620
    edited 2009-06-08 18:25
    Disk drives don't use motors for head positioning these days. It's probably a voice coil.

    Leon

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  • kwinnkwinn Posts: 8,697
    edited 2009-06-08 18:49
    Leon is correct. It is a voice coil type of actuator and needs the magnet in the drive enclosure to operate. It also uses the track information read from at least one of the heads for position feedback. I won't say it's impossible to pull this assembly out and use it for something else, but it is not something I would want to try.
  • heaterheater Posts: 3,370
    edited 2009-06-08 18:57
    kwinn: Give yourself a treat and try it. Once you've got the lid of the drive just undo three screws and you have the voice coil out together with a pair of viciously strong magnets.

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    For me, the past is not over yet.
  • Ken PetersonKen Peterson Posts: 806
    edited 2009-06-08 19:23
    Leon: Technically, it is a motor. Just not the rotary commutated type that most people think of as a motor. If you look up "electric motor" on Wikipedia, this fits the definition. Regarding a driving signal, it does make sense to think of it as a voice coil. Current of one polarity accelerates the head in one direction, and current of the opposite polarity accelerates the head in the other direction. Working against a spring, you would produce a current to position relationship, as the torque on the head assembly is proportional to the current.

    Ken
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-06-08 19:51
    Like heater said, watch those magnets they are vicious, they just love to bite bits off you hands. Great for magnitizing your screwdrivers (and yes I do keep some degaussed, b4 anbody gets purist on me) I tried playing with one but no useful work could be had, but then they were only designed to move minicule little heads that ride frictionless, on air.
  • LeonLeon Posts: 7,620
    edited 2009-06-08 20:17
    Ken:

    But it's not a motor in the conventional sense, as the OP had assumed. It's more like a loudspeaker, which is where the term voice coil comes from. No-one would describe a loudspeaker as a motor.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • TreeLabTreeLab Posts: 138
    edited 2009-06-08 20:18
    @Ken: Why the spring? I think that the position is absolute according to current-generated B field created in the voice coil's loop. The feedback mechanism of reading track info is for precision and to track in the case of vibrations etc.

    Son-of-a-gun ! I had completely misunderstood this part of the coil's operation. Thanks to Heater for the clarification.

    Cheers!
    Paul Rowntree

    Post Edited (TreeLab) : 6/9/2009 12:18:43 PM GMT
  • heaterheater Posts: 3,370
    edited 2009-06-08 20:42
    TreeLab: You need the spring (or something). Ideally the thing is frictionless, and practically runs on a very free high quality bearing. So any little current will apply a force which will cause it to accelerate endlessly until something balances the force.

    Leon: But loudspeakers do have motors. That's what loudspeaker designers/manufactures often call them.
    Even the IEEE ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F20%2F19815%2F00917185.pdf%3Farnumber%3D917185&authDecision=-203

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    For me, the past is not over yet.
  • kwinnkwinn Posts: 8,697
    edited 2009-06-08 20:45
    heater, I have treated myself several times already. I also keep an old 5.25" hard drive without a cover to show anyone learning computer basics. No problem getting the platter, spindle motor, or head carriage out.

    Like Ken said, it is a motor, and it does make sense to think of it as a voice coil. The hard part is controlling it. You could use a rotary or linear encoder to provide position and velocity information to a servo circuit to do so, but to what purpose?

    As Toby said "no useful work could be had, but then they were only designed to move minicule little heads that ride frictionless, on air".

    TreeLab, I am not sure I understand exactly what you mean, but the current in the coil produces a constant force that accelerates the the assembly in one direction or the other. The current determines the speed of the coil, not an absolute position.
  • heaterheater Posts: 3,370
    edited 2009-06-08 21:18
    I always had this idea to build a long case clock based on a HD arm actuator.
    That is have the arm pointing down and swinging a long pendulum. Arrange for some feed back to keep it swinging.

    The feedback pulses also end up driving a stepper motor that moves the hands.

    Not sure how the Prop fits in here, perhaps it could be a digital clock. Timing from the pendulum rather than a crystal[noparse]:)[/noparse]

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    For me, the past is not over yet.
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