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Registered Member #1937
Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53
Well, as i have stated before i am building a coi8l gun for a school project. To demonstrate the safety of this project i would like to show how predictable and controlable a coil gun is. To do so i would liek to use a formula which calculates the smount of winding i would need around my barrel to achieve a certain velocity. I do not kinow such fomula and so am asking you, my dear 4hv community, do any of you know a fomula which could be used to calculate the amount of windings(so most probably calculate the magnetic field and then from there calculate the velocity and then using this formual ain reverse) needed to achieve a certain velocity.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
No formula exists because results are highly dependent on variables such as your specific 3d geometry and the projectile's B-H curve. To arrive at an approximate solution will involve simulating your design using a finite element magnetics package.
However, coilgun design can start with some simple assumptions that help estimate certain aspects. For example, once you've chosen a desired projectile then we usually assume the coil should be about the same length as the projectile. And once we've chosen a capacitor bank, we usually assume an efficiency somewhere between 0.1% and 2% to help estimate the desired coil inductance. This is not the same as a formula for the amount of windings.
However, once you've made a coilgun, the results are consistent, repeatable and controllable.
Cheers, Barry If a pig loses its voice, is it disgruntled?
Registered Member #1937
Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53
Well all i need is some way to prove that my coil gun is controlable, if i build the gun and tell my teacher that the velocity will fall between 50-60fps then that is perfectly fin, i jsut want to be able to control the gun a bit, and make it so it cannot, for example, penetrate the skin, or cause serious harm, at all.
EDIT: i looked at the provided link, looks very promising, i think that is what i need, thank you!
banned on 5/26/2009 Registered Member #1877
Joined: Mon Dec 22 2008, 02:03AM
Location:
Posts: 147
a fun thing called trial and error. xD to measure speed acuratly, u need a chronograph, i think they are expensive, but iv never gone to buy one so i wouldent really know. xD
Registered Member #1917
Joined: Fri Jan 09 2009, 02:38AM
Location:
Posts: 62
Chronys are quite cheap and very accurate. You can't really get by in the field of projectile-launching without one. Good sources are eBay and hunting shops, and the standard models can measure from 30-7000fps, and projectiles as small as a BB gun pellet. If you want over 7k fps, you're going to have to figure out how to build one.
Simulations can yield accurate predictions, but it's hard to beat measurement of reality when it comes to accurate data.
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makign a coil gun with a specific velocity
