The Offical Spudgun Thread

[Event]

The fromula given by 'Event' (f(t) = -1/2gt² + vt + s) is not a very good way to calculate the muzzle velocity from hang time since it completely ignores air resistance. The usual phrasing for this simple formula (in the USA) is;

muzzle velocity(in fps) = 16*(hang time in seconds)
(Assumes s=0, uses g=32fps2)

The problem is the terminal velocity of a spud is only about 90fps, much lower than the typical muzzle velocity, so Vmuzzle is not equal to Vhit the ground because of air friction.

For a hang time of 8 seconds the simple fomula gives 128fps, the actual value is closer to 220fps (for a half-a-spud from a 2" barrel). At 10 seconds, the values are 160fps (simple formula) versus ~400fps.

A more accurate (though still approximate) formula is;

muzzle velocity = 20.955*e^0.2953*t

The above formula is for half-a-spud from a 2" barrel, with air friction proportional to v2 and a coeficient of friction based on a 90fps terminal velocity.

I was owned there, but that is very useful info.

 

[Event]

Questions:

1. Is it a combustion launcher or a pneumatic launcher?
2. If it is combustion, what kind of fuel do you intend to use? What kind of ignition source? Which fuel/ignition source would be ideal, if they differ from the materials you intend to use?
3. If it is pneumatic, will you be using a pressure gauge?
4. Of the two types of launchers, which is usually more powerful?
5. I'm aware that in New York, if you are under 16, it is illegal to own a pneumatic spud gun. Are there similar age restrictions/rules in your area?
6. How much does a project like this usually cost?

1. Combustion (Pneumatic launchers are too expensive)
2. We will be using Ether this time around. We used hairspray last time, but that gummed up the chamber and metal contacts in the chamber, which made getting good sparks difficult. The best fuel is Propane, but rigging a device for the Spud Gun gets very very costly.
3. N/A
4. I'm not sure. I think Pneumatic launchers can be more powerful, but to get that power requires loads of money.
5. As long as we don't point it at someone or something, we're fine. Not illegal. I'm 17, 18 in June, so age isn't a problem.
6. Our last one cost a grand total of $55.