Laser Smoke - How to rock a small mirror back and forth?

Discussion in 'The Projects Forum' started by brianllama150, Sep 15, 2010.

  1. brianllama150

    Thread Starter Member

    Nov 6, 2008
    12
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    Hello

    I'd like to make a piece of wall art involving lasers and smoke.

    To begin, take a poster-sized glass enclosure and put it on the wall. It would probably come off the wall about 2 inches, so we'll say a 36x24x2 glass enclosure. Next, pump in some smoke via tube and fog machine.

    Below the case of smoke, also on the wall, is a green laser in a fixed position, pointing down at a small mirror (say 3" x 1"). This mirror will reflect the laser beam up (parallel to the wall) into the glass enclosure. In order to achieve the desired effect, the mirror will have to be motorized somehow to rock back and forth very quickly to illuminate a cross-section of the smoke.

    Click here if you'd like to see a version of the effect: http://www.youtube.com/watch?v=Fj44Y17EdF4

    Here is a simple picture of the setup:
    [​IMG]

    So how should I power that small mirror? Or is there a better way of doing this? I have limited knowledge of DC motors, but I do know that there would have to be some tricky mechanics to making it rock something back and forth, instead of in a circle. Someone mentioned that I should research how buzzers work (electromagnets and such), but I'm hoping someone here could get me started on the right track.

    I really want to get this working! Please help!
    THANKS!
     
    Last edited: Sep 16, 2010
  2. Dyslexicbloke

    Active Member

    Sep 4, 2010
    420
    19
    Comertial units that do thissort of thing usually use a rotating mirror.
    laser bar code scanners for one.
    Think multi sided drum with mirrored faces, each face sweeps an angle before thre next side takes over.

    I guess you wouldnt be concirned with acurate scanning as long as it was quick enough so no need to use steper motors or anything.

    Just a thought ... simple enough toimpliment partivulaly if you use mylar and not glass.

    If you want to stick with rocking you will be making a galvanometer, essentally a mechanical volt meter with a mirror where the pointer would usually sit. Again looads if you google it.

    The motor is far simpler .....

    Al
     
    Last edited: Sep 15, 2010
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    can u get ur hands on an old fax machine.
    I remember some thing abt this machine. It has a rotating mirror assemble to scan the document. It just might be what u r looking for.
     
  4. campeck

    Active Member

    Sep 5, 2009
    194
    3
    Or you could just do this.
     
  5. campeck

    Active Member

    Sep 5, 2009
    194
    3
    Or this...
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    I've often wondered if you couldn't do the same thing with speakers.
     
  7. Dyslexicbloke

    Active Member

    Sep 4, 2010
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    Speakers with the cones butchered are a popular method of making a DIY galvanometer for laser light show. I'v also seen it done with moving coil meter mechanisms and plastic mirrors. I tried the meter aproach but felt the speed wasnt upto much.

    Last one I built just used a brass nut on a pager motor and added some mylar film to the faces.
     
  8. brianllama150

    Thread Starter Member

    Nov 6, 2008
    12
    0
    Thank you very much! That's what I needed.
    Good ideas all around, you're a lot of help.

    I've seen the light show done with a speaker and mylar online. It looks very simple and cool!
     
  9. bertus

    Administrator

    Apr 5, 2008
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  10. marshallf3

    Well-Known Member

    Jul 26, 2010
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    #1: 50 mW is a lot of laser light. I hope you know what you're dealing with and the safety precautions necessary. If this show you plan to create will be accesible by the public you may need to go through some legal stuff before you're allowed to operate it.

    Class IIIb

    Lasers in this class may cause damage if the beam enters the eye directly. This generally applies to lasers powered from 5–500 mW. Lasers in this category can cause permanent eye damage with exposures of 1/100th of a second or less depending on the strength of the laser. A diffuse reflection is generally not hazardous but specular reflections can be just as dangerous as direct exposures. Protective eyewear is recommended when direct beam viewing of Class IIIb lasers may occur. Lasers at the high power end of this class may also present a fire hazard and can lightly burn skin.


    My guess is you've misquoted the power, a common laser pointer will fall under 5 mW and is considered to be much safer.

    That said, using speakers with mirrors has and is still a very common method for creating simple displays. Typically a 4" speaker with a fairly high excursion cone is ideal. You will want to use two of them set up such that one controls deflection on the X axis and the other for the Y axis. It's just a simple matter of mounting angles to get them to do this and a simple stereo power amplifier serves as an ideal driving source.

    I'd also use true first surface mirrors to reduce distortion, you can find these at most any surplus website including eBay.

    I'd try to keep the speakers intact so the voice coils will remain aligned between the magnet poles. If size presents a problem you can cut the things up but at least leave the spider webbing and accept the fact that not only will precision suffer but depending on the selected speakers they may not work well at all.
     
  11. brianllama150

    Thread Starter Member

    Nov 6, 2008
    12
    0
    With this project, the beam will only be going in one direction (parallel to the wall) and it will definitely be diffused by the smoke.

    Thanks for the info about mirrors. I'll probably just find some small pieces to mess with at my dad's glass shop.
     
    Last edited: Sep 16, 2010
  12. campeck

    Active Member

    Sep 5, 2009
    194
    3
    Yeah but normal laser pointers are no fun! My friend has a 50mW and i've used it for pointing out clusters and DSO's at night as well as noticed the smoke effect the op is talking about. I've always worried that a police officer who saw anyone pointing out night sky objects would probably think you were trying to blind airline pilots.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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