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Thread: Cheap galvo project idea

  1. #11
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    If you really want a homemade galvo that you can actually use for decent stuff you can build Norm's galvo kit. http://norm.servehttp.com/

    It's based on Chan's design that was linked up earlier but improved and made into kit form. Not too bad of a price, although I was able to buy a set of 15K scanners from ajiii for less than the cost of the kit.

    You won't be able to do much with speakers other than draw some very simple distorted shapes. But, I have read that you get a lot better performance out of speakers than trying to use the voice coil mechanism in harddrives. For a long time I researched how to make my own but I realized it is cheaper to buy a 15K set and that is what I did.

  2. #12
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    Yeah I'll probably end up buying a set, but I just can't get over the idea of -how hard can it be to move a tiny little mirror that weighs about 1 gram(?) 40 degrees back and forth at reasonably high speeds. I'm not into precision graphics, just mainly beamshows, so I don't require ultra precise positioning and closed loop stuff..

  3. #13
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    Quote Originally Posted by steve-o View Post
    The resonant frequency of audio speakers varies with size (as well as other factors. A 15" woofer will have a lower resonance frequency than, say, a 5" midrange. When removing the paper part (the cone) leaving only the spider and the coil the resonant frequency will also change.

    Phase shift (current lag) is present in all inductors (including speaker voice-coils) I'm not sure you mean about the 180 degree shift. In an inductor the voltage will lead the current by 90 degrees if I remember my college days correctly (its been 27 years )

    27 years, wow, it is still fresh in memory then because I think you are right about the inductance.

    The phase shift I'm talking about results from the mechanical part and is a property of single spring-mass-damper systems like a speaker or a open loop galvo. The phase shift is between the input excitation force (magnetic force) and the mirror output position.

    Removing parts will certainly change the resonance freq. but I found that it will stay close to the original value (+ 10 or 20Hz). Removing the paper also reduces damping somewhat but not much. I've actually tried all that with a car stereo speaker and the results that I got where not shocking wrt boosting speaker performace. Look here for some stuff I did a while back. My speakers had res freqs. around 100 Hz.

  4. #14
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    Wow! nice work Zoof-
    Looks like you've about done it all!
    Which design did you have the best luck with?

  5. #15
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    Dec 2006
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    the toothbrush was the best

    just kidding, the speaker gave me the best results because the galvos had too much oscillations due to lack of damping and were only a bit faster than the speakers. The hinges of the mirrors on the speakers are crucial, I spent a lot of time thinking about it and came up with pins and heat shrink insulator and balsa only to find that over a few weeks of time the heat shrink hardened and introduced friction thus hysteresis that was pretty bad, even for simple graphics. Norm (as mentioned above) had speaker scanners and used bent straws as the hinges and I think that is a much better design and can be built in an evening time.

  6. #16
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    Zoof-
    Good info.
    Toothbrush .
    I've got a speaker dissected so I may try it just for grins
    Steve

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