Halloween Fog Screen

Written by: NetworkError, on 03-11-2008 22:17
Last update: 03-12-2008 17:55
Published in: Public, Technical Wootness
Views: 15676


This Halloween I built a fog screen for Omniture's Halloween party.  I got the idea from the waterfall effect on the Pirates of the Caribbean ride at Disney Land. The basic idea is to create a flat, thin screen of fog and project an image onto it.  This creates a holographic illusion of the projected image floating in the air.

After some experimentation, it became obvious that directing fog isn't easy.  The fog generated by fog machines is neutrally buoyant.  To get it to move in any direction and maintain its shape (a flat curtain), you have to sandwich it between two streams of air.  (I've also heard you can chill the fog to make it heavier than the warm surrounding air.  I haven't tried this yet.)

My initial design looked something like the diagram below.  After drawing it up on a whiteboard, I Googled for similar effects and found professional machines using a similar basic design.

 

 This is the side view of my fog machine.


This is the bottom of my fog screen machine.  I made the vents out of MDF and attached them to a 2x4 frame.  It's a good idea to make your vents adjustable.


This is a side view.  (The machine is on its side.)  The hole in the side is fitted for a box-fan.  The fans preasurized the outer chambers and creates the outer two jet-streams.


This is the top of the machine.  The three dryer tubes were hooked to three fog machines which were hung from the cross-members.


This is the final effect.  The image is projected through the fog screen.  When the focussed projected image hits the fog screen, it refracts a bit and the image shows up on the far side very clearly.

Improvements I want to make on the prototype:

  • I should have made the fog vent a little wider - about 1 to 1 1/2 inches.
  • I should have built a fogger into the system rather than using regular fog machines.  (They drip a lot and are harder to manage.)
  • I should not have hooked the foggers to dryer vents that bent around a 90 degree agnle.  The back-preasure made them drip a bit.
  • I should have put some fans in the fog chamber to propel the fog out of the center vent.
  • I should have created a floor vent to pull the fog down and out of the isle.  This would have limited the effect of outside drafts and kept the image cleaner by keeping ambient fog to a minimum.
  • I should have used a bank of PC fans (120 mm) for all intakes and fog propulsion rather than using box fans.

 


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