Air reservoir to use epoxy, not epoxy putty

Posted on 2010-07-02 00:27:38

Filed under fang4

After some thought and discussion at SpudFiles, I've decided to use epoxy rather than epoxy putty to plug up the end of the aluminum tube for the air reservoir in FANG 4. Previously I had thought that epoxy would be too much of a pain to work with, but after some more careful analysis, I'm convinced that epoxy is a better choice as it has a higher shear strength, the possibility of reinforcing the resin with a wire mesh for a composite plug, and a proven method of construction.

The shear strength of epoxy often is far higher than that of epoxy putty. I'm not certain how they compare in densities (epoxy putty is lighter than aluminum), however, the higher shear strength will mean that less material could potentially be used in the epoxy chamber. I will likely have to do some sort of FEA to determine if the thickness of the epoxy plug is adequate because it could be so think that it acts like a diaphragm, but that's simply part of the design process and I'm looking forward to learning new techniques.

I'm angry that I hadn't thought to use this before as I would have avoided Catalina Cylinders completely. They make a good product, but their cylinders should not be used in Nerf or spud guns until they are more readily available.

A few weeks ago I asked Jeremy, the owner of SpudTech, if he might be interested in listing aluminum cylinders for use in spud guns. He said yes and mentioned that he'll add them as a pre-order item in the near future. I can't easily check if the cylinders are listed as I'm writing this from a text-only browser (links), but this is something to watch out for.

In other news, I've started looking at impact design for FANG 4. I'm trying to list all ways the current design could be dropped and how to best design the Nerf gun to withstand these drops. Due to a lack of data and test results, FANG 4 will be overengineered. I checked out a book from the UMCP engineering library about plastic failure and I'll be using some guidelines and methods from that book to help design FANG 4.

My job has not kept me busy so far this summer. I anticipate that the biggest obstacle to the completion of this project is my own laziness. I've been getting better in this respect. Blogging will keep me on track.