6mm Coaxial Piston Cannon

[FORE!!!!]

So you do a bit of maths in your spare time hey tech

[c11man]

that math is easy........ what realy pisses me off is when i need the reciperical of a number and have no way of getting it, like when in bed

[twizi]

very nice there have been so many little coaxials these day love the push button

[Mr.Sandman]

Make a silencer for it. BUt otherwise nice job. You should make it a submersable speargun.

[FORE!!!!]

@c11man

does this help?
http://www.mathsteacher.com.au/year7/ch ... ip/num.htm

[Mr.Sandman]

BTW @crowley what is that little nub o your gun? I cant figure out what it is. And @c11 why not keep a graphing calculator at your bedside?

[c11man]

fore, i know what it is but its not very easy to figure .016484 or a similar number.

sandman, i tried that but i cant read the damn thing in the dark

[Technician1002]

So you do a bit of maths in your spare time hey tech

Yes, I do some. It is far faster to do the math than to build 5 sub par launchers. I like to know if it is likely to blow up, work poorly, or give me that extra edge of performance before I build. Then I test and tweak from there. Anyone building hybrids needs to do this just to get the mix close.

Those that don't do the math with pistons are often dissapointed and then spend time trying to find why it isn't working right.

I often have several on paper before I build one. It's why the 3 inch is my next one.

[MrCrowley]

edit 2:
Would I be right in saying I need ~7.3 pounds of force to open the push-button valve at 300 PSI assuming the 'piston' is 5mm in diameter?

Do the math. Unfortunately you have mixed metric an English units. The "piston" diameter is not the correct figure to use for the pushbutton. The force is calculated using the cross section area of the valve seat. This is a little smaller than the diameter of the piston and larger than the operating shaft under the button.

For sake of math the area needs to be calculated, but since forces in pressure and button pressure are in English units, it would be best to convert the dimensions to English and work from there.

1 millimeter = 0.0393700787 inches. 5mm = 0.196850393. First part done.

Area = Pi times Radius squared. Radius is 1/2 diameter..
R = 0.098425197 inches
Radius squared = 0.009687519
Pi times R squared = 3.14159265 X 0.009687519 = 0.03043424 square inches.

Force equals pressure times area.

Force = 300 X 0.03043424 sq in. = 9.130271904. So yes, your figures are in the ball park if your dimensions are correct. The force of any spring will be added to the result.


If I made a math error, feel free to point it out. I am human and do make mistakes once in a while.

Turns out I made the math error. I did everything correctly, including the conversions in to imperial. The thing I did wrong was I used pi x diameter = area instead of pi x radius^2 = area.
I just did the same calculation again using pi x r^2 and I got the same answer as you did.

I am human and do make mistakes once in a while

[MrCrowley]

Update:
Shorter barrel
Scope
Modded blowgun