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john bunsenburner

Thu Mar 26 2009, 10:12AM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

As some of you might know i am building a coilgun for a school project. As i just found out last night the teachers do not feel confortable with ME having soemhting that can potentually shoot a metal object in school. A teacher suggested that I clog the end of the barrel with a piece of sheet metal to make a noise after every fireing. Do you have any other ideas that do not invlolve metal projectiles flying across my school?

Download

Thu Mar 26 2009, 10:35AM

Registered Member #561 Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230

Shoot into sand bags? that would stop all but the biggest coilguns

Barry

Thu Mar 26 2009, 11:41AM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

Shoot a heavier object that moves slower. Then make it blunt so it can't possibly puncture skin. Then show them the projectile and explain that it's as dangerous as dropping it from a height that corresponds to your expected kinetic energy.

For example, if you have 50J stored energy, then optimistically assuming 1% efficiency then it will have 0.5J kinetic energy. The kinetic energy of a moving mass is KE = 1/2 m v^2. Assuming a 20g projectile, solving this gives you a velocity of 7 m/s (or about 15 mph).

To find the equivalent drop height, note that kinetic energy of a mass falling through gravity is KE = mgh. Solving for height in our example of KE=0.5J and m=20g will tell us this speed is reached by dropping it form a height of 2.5 meters which is about the same as holding it over your head and letting go.

This was just an example. Try your own values of stored energy and mass until you have a convincing argument.

Cheers, Barry
If you can't be a good example -- then you'll just have to be a horrible warning.

Bjørn

Thu Mar 26 2009, 02:23PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

What about using a vertical transparent tube and a large heavy projectile so it can't exit the top. That way you can read the energy directly off a ruler on the tube and you can use simple graphs and math to explain how fast a projectile with lower weight would go at the same energy.

john bunsenburner

Thu Mar 26 2009, 03:41PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

Well teachers are mostly concerned about this hitting some ones eye, i had an idea: what if i got fine steel wool and poured it in expanding foam, or soemthign along those lines? Oh and this is for tech not science or math ando so no graphs or calculations will have to be made.

teslacoolguy

Thu Mar 26 2009, 04:01PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

Why not get a clear plastic tube and use that as like a projectile chamber with a sandbag on the end?

Shaun

Thu Mar 26 2009, 04:37PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

I've been in a few situations like yours, and I find the best thing to do about concerned authorities is to not let them get concerned to begin with. First off, you can't use words like "coilgun", because it has "gun" in it and guns kill people. There are plenty of alternatives, like electromagnetic launcher and other terms like that. I used to refer to potato guns/cannons as produce accelerators.

But since you are past the point of simple wordplay, I would suggest calmly explaining to your teacher that what you are making is a low energy, low efficiency device that is not physically capable of injuring a human being (at least the projectile isn't, but don't bring up the capacitor bank!). Many have suggested using a physics argument; that would be my first choice.

john bunsenburner

Thu Mar 26 2009, 05:49PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

My teacher has built several and said that he will be happy to help me one one privately, he just says that in an international school buildign a coilgun is just not a very intelegent thing to do, and he is scared about it hitting someone in the eye, we donnot have the space or time ot construct a shooting range BUT i like the idea of the clear plastic tube as a barrel.

Barry

Thu Mar 26 2009, 11:47PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

Your teacher has built several, and is still more concerned about eyeball safety than capacitor bank safety? That seems strange.

Oh well, more policies are formed for fear of litigation than for actual sensible safety issues. And when lawyers are involved then all reasonable logical thinking goes out the window. The legal system has no logic to it at all, anything can happen, including making hot coffee "safe" by labeling the contents "caution contents may be hot". Sheesh.

Good luck.

john bunsenburner

Sat Mar 28 2009, 01:44PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

Well I will have the coil gun in a little plastic box, and will try not to get anyone btu my self close to this. I have managed to convince the teacher that i can make it, i will just make it use a plexy glass barrel and put a bolt on the end, perhaps ill put an led light on the and then after shot there will be a little flash of light, I will see. the velocities will be kept under 5m/s anyway. As a little bit of irony;
That teachers class is building a railgun at the mement, anyway I will keep it safe.

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