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After some experimentation, we went a different direction with our air cannon. We put a sheet of non-elastic material across the bottom for visitors to whomp. It's loosely attached and moves a decent volume of air when it's struck. Because the cannon is angled upward 45 degrees or so, it tends to fall downward again after the blow has been delivered. The material is a rubberized cordura (whose trade name, manufacturer and supplier are known only to a colleague who is on vacation) which is kinda like backpack fabric. Works just fine.

David Savory
Community Extensions Program Developer and Exhibit Curator
Science World British Columbia
TELUS World of Science
1455 Quebec Street
Vancouver, BC
Canada V6A 3Z7

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-----Original Message-----
From: Informal Science Education Network [mailto:[log in to unmask]] On Behalf Of Erich Rose
Sent: Thursday, September 17, 2009 7:41 AM
To: [log in to unmask]
Subject: Air Cannons

ISEN-ASTC-L is a service of the Association of Science-Technology Centers Incorporated, a worldwide network of science museums and related institutions.
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Hey folks,

I am running into a bit of a problem specifying the correct elastic material for an air cannon. I have worked on several of these and we always used black neoprene rubber sheet. We used material already laying about the shop so I had to guess at the proper durometer. We used material 1/16" thk but it would tear fairly easily.  For the one I did recently I specified an elastic natural Gum rubber with a durometer of about 40A. It proved way too stiff.  The folks at McMaster-Carr have suggested an Ultra-elastic Natural Latex rubber with a durometer of 35A.

The cannon is smaller than most at 8" diameter versus the usual 12-18" diameter ones most of us have built. But it is shooting a shorter distance and the mock up worked well with a plastic bag as diaphragm.

Can anyone offer a specification for a good elastic diaphragm? 

--
Erich Rose
Exhibit, Environmental and Industrial Design
807 The Living End
Austin, TX 78746
512-626-9930; [log in to unmask]

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