FANG 4 status update #1

Posted on 2010-06-28 23:23:19

Over the past few months, I've been planning a semi-automatic Nerf gun. This is a fun project that involves most of what I've learned as an undergraduate engineer and forces me to go beyond what I was taught. I will use my blog to detail the design process, partly for the benefit of any online readers I have, and partly for my own benefit. I will detail precisely what I do to design this Nerf gun so others can use the same techniques to make better Nerf guns and make the game even more fun.

Lately I have changed my ideas too often. FANG 4 was originally conceived as a scaled down version of FANG 3 including a turret and an air tank from Catalina Cylinders. However, I became annoyed with the inaccessibility of Catalina's cylinders. I also started thinking that more than 30 shots from a single tank is unnecessary. At the same time, I started thinking about making a simplified bullpup pneumatic Nerf gun (inspired by this air gun) that uses a hopper clip. The gun would use latex tubing as the air reservoir; McMaster-Carr sells reasonably high pressure latex tubing that I initially thought would be appropriate. After a fairly detailed analysis, I came to the conclusion that making an efficient pneumatic Nerf gun that used a hopper clip would be difficult. As efficiency is one of my primary goals, I decided to postpone this gun until after FANG 4 is complete.

I was intrigued enough by the idea of latex tubing, and I wanted to use the bullpup layout to to shorten the gun. Length affects transportability, general mobility, among other things, and in general shorter lengths are better. So I redesigned FANG to use what I previously called the "barrel mover" design much like CaptainSlug's ABP5K and similar to PVC Arsenal 17's RSP-Skeleton without shells. The barrel moves around the darts. I considered a similar design for FANG 3 back in January. On 2010-06-22 I essentially redesigned FANG 4 along these lines.

I promptly ordered some latex tubing for testing... and the testing did not go so well. I'll detail in more detail why I wanted to use latex tubing for an air reservoir, what went wrong, and why I did not choose latex tubing in the end in a future blog post.

This morning I reconsidered something I had dismissed a long time ago (FANG 2!) before I learned about Catalina Cylinders' air reservoirs: thin extruded aluminum tubing. I discounted these tubes earlier because they "had" to be welded to be useful. I started thinking about boltsniper's paintball gun and realized I could probably use some sort of plug with an O-ring. I still considered welding, but the alloys easily available were heat treated and welding would reduce the strength near the weld. Not to mention that I don't know how to weld. Eventually I realized I could use epoxy putty, a small cylinder of aluminum, and a pipe tap, and these problems disappeared. I'll detail the mathematics used in the design of this air reservoir in a future blog post.

So where does this leave FANG 4? I rethought the design and decided I could make it more compact and sturdy by putting the air reservoir inside of the turret. I considered this earlier when I was thinking about turrets and latex tubing, but I also wanted to make the tubing accessible for replacement, and that influenced my decision to not use a turret for that design.

The current design is shown below. This is a rough drawing; I'll start hashing out some of the details over the next week or two and begin construction as soon as possible.

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Last modified on 2010-06-28 23:23:19.