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Thread: OpenGalvo

  1. #1

    OpenGalvo

    I'm trying to design some incredibly cheap replacement galvos that could be used in any SLA printer for under $15/galvo using parts people probably either already have or can buy from Ebay. My initial results are hopefully attached.

    The mirror (its back visible in picture with coil and magnet attached) was later mounted to the dental floss. The frame is the bottom of a dish detergent bottle. The floss was tightened by a combination of the natural flex of the frame and by twisting a toothpick which was secured in place by friction with a solvent welded abs hook from a failed print of comet 67p (in white on top). The mirror was mounted by friction to the floss by sandwiching the floss between the two little neodymium magnets. Unfortunately the coil on the back of the mirror didn't provide enough/any damping so the assembly is useless despite being able to get a good range of angles precisely with under 5 volts. I suspect this is because for eddy currents to properly form it must be a closed loop and the wire on the back currently is not a closed loop. I might try using a piece of copper foil instead as that's thicker than aluminium foil/nashua tape I also added and would make it easy to cover the entire surface area. I think that even that won't be enough though so I'm going to next try mounting the mirror rigidly to a stainless steel needle mounted between two broken glass christmas tree light tips. (extremely low friction and cheap) From there I can introduce damping by simply adding some tiny rigid flaps elsewhere on the the needle that can use wind resistance to break similar to how the inside of a music box regulates its rotary speed.


    Other approaches I might try are on this page: http://spt06.chez-alice.fr/00/scan1.htm
    Last edited by amoose136; 08-25-2016 at 03:25 PM.

  2. #2
    So I soldered the damping coil into a closed loop and that made no difference. Copper foil on the back also makes no difference. The oscillations are the death of this design even though I am able to precisely control the angle with only a 5 volt source and not much current.

  3. #3
    Senior Engineer
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    That needs a capacitor across it and that will stop the oscillations if you get the value correct.

  4. #4
    Quote Originally Posted by Mjolinor View Post
    That needs a capacitor across it and that will stop the oscillations if you get the value correct.
    Interesting idea. I might try that but I suspect the damping coil simply isn't having enough of a current induced in it.

  5. #5
    No luck with the capacitor. There are still far too many micro oscillations that last many minutes after perturbation. I'm moving to plan B but this could take a bit as I need a needle sharpened on both ends and I need a custom encloser to hold the needle. This encloser will be FDM printed for now but I'm still designing it.

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