8 wire stepper translation

Discussion in 'General Electronics Chat' started by stubbornTryHard, Mar 26, 2013.

  1. stubbornTryHard

    Thread Starter New Member

    Dec 19, 2012
    I'm playing with the internal organs of an old camcorder (VHS - remember them ?).... specifically the lens mechanisms.

    On the aperture control, there is a stepper giving me grief.
    I know that I can see 4 equal values/coils using only 4 wires:
    Black-Purple, Purple-Blue, Blue-Gray, Grey-Black
    ... but that's about where I get lost.

    If there were to be other values, I was expecting them to half or doubles, and they are not.

    I then have the Red, Yellow, Brown, Orange ... !?

    (if it helps, BPBG & RYBO were originally bundled into 2 groups of 4, both heading off to different PCBs on the camera - before it got rudely ripped to shreds.)

    I can 'feel' a logic, but just can't pin it down to anything solid (yet!)
    Not like any motor I've played with before, nor wiring i can find on Google.

    Has anyone got any insight based upon the resistance info below ?

    Any help appreciated !!

    Ohm tests (sorry, I tried to format, but it just gets re-formatted !)
    Black Purple Blue
    Purple| 988
    Blue | 684 995
    Grey | 992 1455 998

    Red Brown Yellow
    Brown | 1043
    Yellow | x x
    Orange| x 1044 150
  2. stubbornTryHard

    Thread Starter New Member

    Dec 19, 2012
    Ok, so 94 views and no replies .... that means that I've asked a dumb question, or I've a unique motor that no one's come across before.

    .. anyone mind telling me which ?

    Happy to reword the question or provide further details if necessary :)

  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Photo? Diagram of wires showing ohms and connections between wires? Your description is not great.

    Normally if there are 8 distinct and equal motor wires it is a 2 phase stepper with 8 wires. That is common in large motors but incredibly rare in tiny specialist motors.

    Your description seems to imply 2 groups of 4 wires "going to different PCBs" which would mean some very special type of motor with unusual wires, possibly encoder or feedback coils.
  4. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    An encoder is what I was also thinking for the two sets of wires.

    Another possibility is that there are 2 motors or it is a motor solenoid (rotation plus shaft extension/retraction), so aperture and maybe focus puller, or shutter cycling.

    And for formatting when in doubt screen cap a spreadsheet and post as a picture, but you might manage by including the table in code tags and trial and error in previews.
    Code ( (Unknown Language)):
    2.     A    B
    3. C    0    1
    4. D     1    0
  5. stubbornTryHard

    Thread Starter New Member

    Dec 19, 2012
    Thanks for the comments. appreciated.
    I have a little progress, and more notes/images.

    For progress, I've managed to remove the 'motor' and get a peek inside.. although not a full dis assembly !

    The mechanical output is simply a pin on an arm, whose extent of travel is maybe 8mm , a rough approx of 45 degrees.
    The pin/arm has an internal force returning it to 'home' position.
    The movement of the pin in the range shown, moves the (not shown) lens aperture fully open/closed.

    By applying voltage to Yellow/Orange & Red/Brown, I am able to get the pin to move to it's furthest extreme, or to 'float' in situ (where the internal force is roughly matched by the force of voltage applied).

    In the pictures you can see 2 coils connected to red/yellow/orange/brown, and I at this stage believe cause the actions listed above and detailed further below.

    What is underneath those is hard to say without a full disassembly, which I am considering, but tbh, scared to death of ... it doesn't look easy (for me).

    I'm not expecting a full solution here - but if someone could give me any clues as to how to progress or what to test for, or theory on how to control the extent of travel ..
    .... would be muchly appreciated !




  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    It looks to be a rotary solenoid with two drive coils, probably sine/cosine drive or push/pull type drive.

    The other wires are likely to be feedback, maybe resistive feedback like a pot.

    To drive it you need to apply PWM to the coils under closed loop control which will then hold the output pin in the desired position.

    Basically it will be a pain the butt to drive unless you just want it to move between min/centre/max as a simple 3 position solenoid.
  7. stubbornTryHard

    Thread Starter New Member

    Dec 19, 2012
    Sorry for not giving feedback or thanking you earlier.
    I have played with feeding the little mite PWM, tring to balance one coil against the other, and you are of course tight ... a pain in the butt.

    Taking a step back, I realised that in it's new life, this lens unit is not going to be doing anything quite as sophisticated as it was in it's previous life.
    Hence a simple equation of effort vs. gain - pride.

    I'm going to simply select a new motor/gear to open/close the aperture.
    A simple one, with instructions ;)

    But many thanks for your help, I hate to give up without at least trying and learning a little.
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Thank YOU for posting the final result. :)

    Many other people are rude/selfish and ask for advice, get advice, then are never heard from again.