COIL GUN (It didn’t work)
Justin McGowan, Brock Hulse, Jacob Friedhoff, Kevin Haudbine, Derek Maidel
At it’s core, a coilgun is a tube with a variable amount of electrically powered coils along it. A ferrous projectile is accelerated through these coils by powering them - making them electromagnets - in a precisely timed manner, which draws the projectile towards the center of the coil and then cuts the power off right as it hits halfway through. Normally, this is done through clever circuitry with IR gates which can tell when the projectile passes by the center, letting the rest of the circuit know that it’s time to cut the power to that one and power up the next. By doing this, the projectile is slingshotted through the series of coils and shot out of the other end of the tube. The coilgun has the potential to reach extreme velocities, but they aren’t widely used as actual killing devices because of the large amount of power necessary to make the coils accelerate the projectile with such force. It’s simply not practical to carry around a large enough power source to make the electromagnets that strong. In a coilgun, the only really changeable things are the number of coils, the amount of voltage applied to those coils, and the length of the tube. The purpose of this experiment, then, is to find the relationship, if any, between manipulating the voltage applied to a single-coiled coil gun and the velocity at which a projectile is ejected. We believe that when the voltage is increased, the velocity will increase as well, and when it’s decreased, the opposite will happen. Our reasoning behind this prediction is that the electromagnet will draw the projectile forward more or less powerfully, which would affect the final speed in a similar way. Controlled variables will include the circuit which will provide power to the coil, the firing position, and the projectile.
Diagram:
The main materials used in the project were electrical components, specifically a transformer, multiple resistors (¼ watt, 1k ohm), two large capacitors(350 volts, 2500 microfarad), copper wire (~50 feet), pvc pipe (2 feet), insulated magnet wire (~300 feet), and a ball composed of magnetic metal. Earlier in the testing, smaller capacitors were used, but it was determined that the amount of wire being used would require larger capacitors that could store more charge. Primarily a smaller transformer was in use and there was a wooden plank that the entire circuit was organized on. The transformer was later replaced by a power supply that offered more options for what amount of DC current would be in the circuit. Observe the diagram to see just how the circuit was organized. As stated a few times throughout this paper, the setup was based on http://coilgun.info/mark2/home.htm. To launch the ball, a button would simply be pressed, activating the magnetic wire for a short span of time and the momentum of the ball would carry it through the tube. All in all, the design was greatly simplified by the end of the project, but the changes made would have only eliminated potential issues in the designs that caused flaws in the system.
In order to collect data, a timer would be started as the projectile would leave the barrel. A length of a meter would be laid out, with another meter stick on the other side creating a sort of tunnel. There would then be an object to stop the projectile after one meter. As the projectile was stopped, the timer would stop. We would then find the speed by taking the total distance (onemeter), and then divide it by the total time it takes for the projectile to travel the single meter. We would then try this with the capacitor charged to different voltages.
Since we were unable
to record any results on our own, we have some results from another experiment
which can be found here: http://coilgun.info/mark2/resultvoltage.htm,
and here http://coilgun.info/mark2/resultposition.htm.
Our original design was modeled after this experiment so we were expecting
similar results.
|
Dist (x) |
Muzzle Speed (m/s) |
|
18.6mm |
4.46 |
|
20.4 |
4.67 |
|
21.5 |
5.00 |
|
22.5 |
4.73 |
|
24.0 |
4.26 |
|
26.8 |
3.73 |
|
28.5 |
1.25 |
The data he received shows that varying the depth that the projectile was put into the coil would produce differences in muzzle speed. As our project evolved we changed our focus to varying the voltage instead of the depth. We were going to hold the projectile in place and change the voltage. Results for this new hypothesis can also be found by the same person and can be seen below.
|
Volts |
Speed (m/s) |
|
5v |
0 |
|
10v |
0 |
|
12v |
1.56 |
|
15v |
3.40 |
|
20v |
5.24 |
|
25v |
6.01 |
|
30v |
6.40 |
|
35v |
6.61 |
|
40v |
6.74 |
|
45v |
6.91 |
|
50v |
6.96 |
|
55v |
6.75 |
|
60v |
6.26 |
|
64v |
5.91 |
It should be noted that from 0 to 10 volts the projectile did not even make it out of the barrel. From 12 to 20 volts the speed increased by ~1.7 m/s. After 20v the increase in speed started to decay until it topped out at 6.96 m/s at 50v. Above 50 volts the speed began decreasing.
It is not possible to put error bars on this as we are not sure the accuracy of the equipment used or the uncertainty of the data.
In the end we were truly unable to fire the coil gun consistently even after hundreds of attempts, hundreds of dollars, and close to twenty hours in hands on labor. Every team member as an individual researched on their own time and also agreed on the precise construction of our circuit. As a team we were grotesquely baffled as to why our gun would simply just not fire even though we tweaked almost every aspect to see their respective outcomes. We hope there is honor in accepting that we failed. As stated before, we believe that when the voltage is increased, the velocity will increase as well, and when it’s decreased, the opposite will happen. Based off the data collected from our third party it is safe to say that indeed as voltage increases or decreases velocity will increase or decrease proportionally. One caveat that occurred though is that once the capacitors reached a certain voltage the velocity hit a peak where it could not increase linearly. This, which can be referenced above, ended up in a bell curve. The data turned out the way it did because, logically, if more power is put into a system more power will be put out. Just in this situation more power being put out is in the form of projectile velocity and power being put in is in volts. At first our own problem was with a faulty transformer. It then became known that we also had a problem with the capacitors. Then, even the button we were using to trigger our gun discontinued to function properly and caused the capacitors to discharge incorrectly and seep power. In the end we changed all of these factor but alas, the coil refused to fire and we were all genuinely stumped. As far as our procedure went it could not have been more foolproof. Other than foolproof it was also simple, and should have worked
nicely yet here we are. Overall the only other thing we could have done was to follow directions on how to make a coilgun online exactly, but that would have made our experiment unoriginal and therefore not our own.
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"For Love of a Gun." - IEEE Spectrum. N.p., n.d. Web. 31 Oct. 2013. <http://spectrum.ieee.org/consumer-electronics/gadgets/for-love-of-a-gun/0>.
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"World's Coilgun Arsenal." World's Coilgun Arsenal. N.p., n.d. Web. 31 Oct. 2013. <http://www.coilgun.ru/>.
http://en.wikipedia.org/wiki/Coilgun - This is the wiki page for coilguns. Basically any information about coilguns can be found here (other than how to build one).
http://www.anothercoilgunsite.com/ - The guy that runs this site made a coilgun very similar to our design. We tried to follow some of the same specs as him.
http://www.coilgun.eclipse.co.uk/ - This site is a treasure trove of information on coilguns. The theory tab is the coolest part. Every part of a coilgun is broken down and the mechanics and physics of each individual piece is explained.
http://www.deltaveng.com/portable-coilgun/ - This is an example of what we would have loved our coilgun to look and function like. Sadly it didn't.
http://coilgun.info/about/home.htm - Another series builds. We also looked to try to replicate some of the specs in this build.