FANG 4 design goals

Posted on 2010-06-28 23:48:19

Filed under fang4

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. These goals essentially are things to keep in mind during the design process.

Durability and impact resistance - Most Nerf guns won't survive a 10 foot drop. Durability in general is a serious problem. While I'm not designing my gun to be indestructible, when possible I'll make an effort to make the gun more durable. To do this I've started studying what breaks are common in homemade Nerf guns, determining how to rubberize areas or if rubberization would help, using high safety factors, looking at material fatigue, etc.
Ease of disassembly - If anything requires adjustment, replacement, or upgrade, I want that to be easy. This Nerf gun is experimental. I will use a single screw size and Phillips head screw drivers. I also will minimize the number of screws (within reason) and the number of panels that need to be removed to access a component.
Ease of firing - The trigger can't be hard to pull. The handle can't be uncomfortable. The grip must be adequate. The weight can't be too high. This one's pretty simple.
Precision, accuracy, and ease of aiming - I want the gun to be as accurate as possible. To me, this basically means that iron sights should be part of the design and the sight radius as long as possible (within reason). Things that make aiming difficult (like a piece obstructing the view) must be avoided.
Fast aiming - FANG 4 should be aimed quick if necessary. This basically means that the moment of inertia about the handle and person should be low. That means that the mass should be as low as possible, the gun should be as short as possible, and that the center of mass should be as close to the user as possible. Additionally, if the sight can be made easier to use, that helps.
Ease of carrying - I want a gun that can be carried easily. Low weight is important, as is the existence of handles.
Ease of transportation - This is similar to ease of carrying, but I have the ability to fit in a box in mind. Gun length is important, as are special features like folding or collapsing components.
Ease of loading darts - Darts should be as easy to load as possible. Funky shells or clips tend to get in the way, as do weird gun designs.
Ease and speed of tank charging - The gun should ideally charge quickly. This is determined by a large number of factors including all those that affect comfort, the gun's performance and efficiency, the size of the air tank, the pump, etc.
Mobility, agility - FANG 4 should be as mobile as possible. I have mass in mind primarily here, but anything that applies for fast aiming also applies here.
Rate of fire - The gun should be able to fire at least at a certain rate of fire. There aren't too many restrictions to this aside from what mechanism is used.
Reliability - Reliability may be the most important goal. It's determined primarily by the reliability of the mechanisms used.
High shots per tank - This directly opposes the goal of fast charging. "High" is completely relative too. Right now I consider "high" to be 10 to 15 shots with anything more being frivolous and detrimental to ease of charging.
High shot capacity - Whatever system that stores darts ready for firing is used, I want it to carry a good amount at the very least.
Range/muzzle velocity - FANG 4 should get the desired range goal.
Safety - Safety is another extremely important goal. Nearly every component has the opportunity to be unsafe, so I have to keep this in mind in everything. The most pressing issues, however, is the perception of an unsafe gun, and I'll try my best to make the gun seem as safe as possible.
Ease of counting loaded darts - This one's pretty simple. I want to be able to count the number of darts I have available as easily as possible.
Ease of venting tank - I want the air reservoir to be easy to vent after a round of a Nerf war. This is primarily influenced by the position of the venting valve.
Ease of checking pressures - I want to know the pressures the gun is operating at for safety, consistency of performance, as well as my own curiosity. The design should include pressure gauges when appropriate and make them accessible.
Gun stiffness/movement - Many guns seem to be very flimsy. FANG 4 won't be. This gun will be solid.
Leak avoidance - The design must avoid leaks as much is possible. Generally this means I should avoid seals that can be difficult to get to work right... like those in homemade piston valves, homemade pumps, and homemade air cylinders.
Quiet - The gun should be quiet to shoot, pump, as well as vent. Quiet when shooting is possible with an efficient design; quiet when pumping is possible with a well lubricated pump and the right choice of valves; quiet when venting might not be possible, but an exhaust muffler can help.
Upgradability - FANG 4 is experimental, so it should be as upgradable as possible.
Long lifetime of gun - This overlaps a good bit with durability. I want FANG 4 to last forever. This is different from durability, however, as it includes the possibility of maintenance.
Consistency of performance - FANG 4 should hit whatever range I want consistently. This is important for accuracy.
Fast time to target - I want my darts to hit the target quickly. This goal was added at the end when I realized that slow darts can get good range, but not hit the target too quickly. Additionally, really fast darts can slow down a lot and take a while to hit the target; my goal is what actually matters.

I'm certain I forgot an idea or two to satisfy each goal, but this is reasonably complete. I'm receptive to suggestions.

A future blog post will detail the engineering metrics I have and how the goals and metrics are connected.