Posted on 2010-06-28 23:23:19
Filed under fang4Over 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.
Nice to see you here zeda.
I'll start making a 2D drawing of my plans tonight and will make a blog post... this should be fun.
I'm happy to see you're considering a standard hand pump again. Good luck with the build.
Are you going to finish FANG 3 with the rotary barrels? I'm a little disappointed
In your sketches that you probably made in class you seem to include a pneumatically actuated cycling system, but I don't think this matches your goal of efficient air usage, just imagine the pneumatic energy involve in a strong reliable cycling system which will all have to come from your manual pumping, and that's not very efficient
I think 30 shots is pretty reasonable, not all 30 shots have to get good range but a capacity around 30 shots will ensure only minor pressure drop between the first few shots the rest will be there if you need it but most of the time you can just pump it between shooting.
In general I'm not very sure what's wrong with FANG3 that your going to shelf it
The most significant reason FANG 3 is done is that the cylinder is broken. The fitting became jammed in the neck due to galling. Another significant reason is that I have a number of improvements in mind.
Cylinders are not necessarily inefficient. The energy losses due to the pushing are surely low, especially given low friction. Regardless, no matter how you do it, the energy expended to advance a dart has to come from the operator, so all we can do is minimize that energy.
I'll finish my current FANG 4 design in late December at my parents' house.
©2007 - 2010 Ben Trettel
Last modified on 2010-06-28 23:23:19.
Wow, that is one of the best designs for a pneumatic gun that I have ever seen, and I look forward to seeing it during construction.
Posted by zeda on 2010-06-29 13:18:09