http://trettel.org/blog/ Random musings on various nonsenses, updated seldomly. http://trettel.org/blog/86 I have no use for a blog at the moment. Posts deemed worth of preservation will be kept online. All other posts will be deleted. Expect big changes to trettel.org sometime this summer. Sat, 2 Jul 2011 18:57:04 EDT http://trettel.org/blog/85 I'll be hosting my Nerf projects at btrettel's Nerf blog from now on. I'll also slowly create pages for NerfEngrWiki, the Nerf engineering Wiki. Expect all FANG 4 updates to be made at the new blog. Sun, 9 Jan 2011 10:27:49 EST http://trettel.org/blog/82 This week I'm going to make an effort to finish at least a part of FANG 4. The design has been done for well over a month now. I just need to construct it. The main difficulties at this point are having adequate free time and having free time when the UMD mechanical engineering shop is open. UMD has a short break from November 25th to 28th. At worst I'm going to finish FANG 4 then. Hopefully FANG 4 will be a welcome break from the recent fad of pump action springers in the homemade Nerf gun wo Sat, 16 Oct 2010 22:12:26 EDT http://trettel.org/blog/79 After several attempts to write coherent design posts, I've decided to scrap the project of documenting online how I designed FANG 4. I'll probably detail a good deal about the design after FANG 4 is done. I'm going to make an effort to finish FANG 4 within the next two weeks. This may not be a particularly easy task due to scheduling, transportation, and the availability of a machine shop to me. Nonetheless, I'll see what I can do. Wed, 21 Jul 2010 22:46:46 EDT http://trettel.org/blog/77 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 streng Fri, 2 Jul 2010 0:27:38 EDT http://trettel.org/blog/76 In my last blog post, I detailed the reasons behind my decision to use a turret. In the design of a turret, one might want to minimize the amount of material used. In FANG 2, the material I used for the turret cost $15 per cubic inch, so I needed to minimize the amount of material used. A better idea might be to avoid expensive materials, but I did use math to minimize the amount of material by making the minimum distance between each barrel's surface (i.e. the minimum thickness of the turret ma Tue, 29 Jun 2010 11:46:26 EDT http://trettel.org/blog/75 Possibly the biggest choice I can make in FANG 4 is which dart advancement mechanism to use. There are many options available today, and the problems of my past FANG guns all centered around the dart advancement mechanism. Advancement mechanisms considered Barrel mover - The barrel pulls back over a dart in a magazine. Example: APB5K Projectile pusher - A dart is pushed from a magazine into a firing area. Example: FANG 1 Breech closer - A breech closes so that the captured dart can fire. Tue, 29 Jun 2010 10:45:52 EDT http://trettel.org/blog/74 Back in July 2009 my brother and I did a limited amount of testing with typical Slug darts that I made to determine their approximate drag coefficient. The drag coefficient of a 2 inch long Slug dart is about 0.34 with the reference area being as is convention in the exterior ballistics community. The 95% confidence interval is 0.28 to 0.40 (n = 9). One outlier was removed from the data set. These darts were not of the best quality. Your results may vary. This data may be useful for rough estim Tue, 29 Jun 2010 0:23:10 EDT http://trettel.org/blog/73 As a challenge to myself I'm trying to make the best possible pneumatic Nerf gun for the Nerf wars I can attend. I spent a good amount of time thinking about what goals I want and how to achieve these goals. I made a rough House of Quality primarily to rank the engineering metrics and to see the connections between the goals and metrics. Below I'll detail the goals I have identified so far. Obviously, FANG 4 is a semi-automatic pneumatic Nerf gun. These goals are different than that larger goal Mon, 28 Jun 2010 23:48:19 EDT http://trettel.org/blog/72 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. Lat Mon, 28 Jun 2010 23:23:19 EDT http://trettel.org/blog/56 Yesterday I attended my first non-casual Nerf war. I brought FANG 2 in it's partially complete state along with me. I used a single aluminum barrel attached to a PVC coupler as opposed to a turret assembly. For having an unfinished gun and no prior experience, I did fairly well. During the capture the flag games I never was hit. I don't know if that was because people ignored me because they assumed I stank or if they feared my blaster. As I had hoped, the war's given me a few ideas about Mon, 6 Apr 2009 15:25:55 EDT http://trettel.org/blog/49 It's been hard to motivate myself to do anything of importance this spring break, but I have seen a good deal of interest in finishing FANG 2 prototype 1 so I'll give it priority. A few simple things need to be functionally complete: A wooden handle needs to be made New polycarbonate pieces holding the valve and air reservoir holder together need to be made. The current ones were meant to get a good idea of the dimensions (Yes, I am making some of this up as I go along). Polycarbonate pie Wed, 18 Mar 2009 23:14:25 EDT http://trettel.org/blog/48 The image above shows the lines in one piece made with the FDM process. The piece shown (the back end of the turret) actually might need to be remade with FDM due to some warping in the original piece. One corner was warped so that it was not perfectly flat and thus would not seal. Sanding everything flat just made the problem worse (go figure). I epoxied a circular piece of polycarbonate to the back end--this should remain flat. It won't be as pretty as the original plan but it should wo Sun, 15 Mar 2009 10:20:33 EDT http://trettel.org/blog/46 ...or nearly. They still need some post-processing like holes drilled and sanding, but the FDM part is complete. A total of 2.97 cubic inches of material was used at a cost of $15 per cubic inch for a cost of $44.55. FDM isn't cheap but I could do things I'd never consider doing otherwise. Tue, 10 Mar 2009 15:21:57 EDT http://trettel.org/blog/44 With my 3D CAD models complete, I'm finally going ahead with fused deposition modeling. I was given a quote cost at $40 to $45, which demonstrates that this method isn't particularly cheap, but factoring in the machine time I'd spend to make comparable parts with manual machining, it's probably worthwhile. From what I know, the PIRLS lab where these parts will be made can take about a week before the parts are done. The parts are first made, and from what I know they are made solid, with hole Sat, 7 Mar 2009 11:45:37 EST