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Coilgun 1A
Loneoceans
/ Loneoceans Laboratories / EM Propulsion / Coilgun 1A
13J Single
Stage Learning Coilgun
Introduction and aims.
Since this is my first coil gun,
and also my first project to do with electromagnetic propulsion, the
aim of this project is to construct a simple and working single stage
linear electromagnetic mass accelerator to better understand the
workings of this type of propulsion systems and to be a basis for my
further higher powered projects. This will be used to research
and demonstrate the principles of magnetic acceleration, and the
accelerator is to be kept as a test bay for different coil/projectile
combinations. The use of a single stage keeps design parameters
simpler and leaves more room for experimentation. Furthermore, this is
my first attempt at building one and therefore, the power would be
kept low. This coil gun would be built from a used disposable camera.
Cheap and easy! A high voltage sign is printed to warn others from
receiving a nasty shock!
Power Source
Being my first project, I shall
start with cheap and simple stuff. Power source is 2 electrolytic
capacitors fitted into a used disposable camera casing (which will
house the electronics as well). Both capacitors are rated for 330VDC
and store 120uF charge. This amounts to 6.534 Joules each or around 13
Joules in total. The capacitors are connected by wires fitted within
the casing. Although total power is quite small, it will work.
Furthermore, beginners should always start with less dangerous levels
of high voltages and current. Starting small is good. However, it
rarely charges to 330V, and almost always stops at 300V (i believe it
is due to the lousy charger) and therefore 300^2 x 0.5 x 0.00012 = 5.4
Joules x 2 = about 11 Joules total energy.
Switching
This
coil gun utilizes a spark gap as a switch. Noisy, loud, bright and
scary, it works. Following projects would employ a solid state switch
which would make the coil gun totally quiet. For now, the low ratings
make this a feasible solution. In the photo, you can see the two red
wires sticking out. Connecting them together makes the current flow
through the coil. Switching is just connecting the two red wires
together. Sometimes, the spark heat melts the two wires together and
they have to be cut. Much energy is lost however, through this
switching devices. Gives some people a nice scare.
Charging
Since used disposable cameras
already come with their own charging system, I used the one which
comes with it. However, since I added another capacitor, charging
takes around twice as long and makes a nice high-pitched whine. It
works :)
Coil form, Barrel and Projectile
Here both the projectile and
the plastic pen tube around which the coil will be wound are shown.
The projectile is a 2mm thick, 25mm long piece of metal. It fits just
nicely in the pen tube (barrel). The coil form is a 3mm inner diameter
pen tube with 2mm thick walls. Such thick walls make the efficiency
low however, but it was the best barrel I could get with such limited
resources. It is 13.5cm long. I used 0.6mm magnet copper wire. The
coil is 4cm long, 5 layers and has an estimated 200 turns. You can see
a comparison in the photo.
Measuring Projectile
speed
I used two methods of calculating
projectile speed, the distance/height method and the acoustic method.
Distance Method
I set up the gun and had a white
backdrop with a ruler placed there too. I took a picture (with flash)
of the projectile in flight. I then measured the distance it had
travelled and the height it had dropped with the ruler in the picture,
and calculated the speed.
The projectile travelled a distance
of 143mm and had fallen 11mm. Using the formula Speed = d * SQRT(g
/ 2h) , where d is horizontal distance in feet (or meters) ; h is
vertical distance in feet (or meters) ; and SQRT is the square root
function. Taking gravity to be 9.8m/s2, 0.143 *
SqRT(9.8/2x0.011) = Speed = 3.018m/s
Acoustic Method
I placed a microphone by the coil gun setup. Using the sound card and
microphone on my computer to record a shot. Then I edited the
recording and then used the time scale on the audio software to
measure the time between firing and impact. I did this two times and
here are the results.
Test 1: Fired at 03.15216 sec, Hit
at 03.23216 sec, 0.08 seconds for 25cm, (1/0.08)x0.25 = 3.125m/s
Test 2. Fired at 04.16375 sec, Hit at 04.23815 sec, 0.0744 seconds for
25cm, (1/0.0744)x0.25 = 3.360m/s
The average speed would be closer to acoustic test 2 for in the
distance test and acoustic test 1, the capacitors were not fully
charged.
Back to the
Laboratory Index
(c) Gao Guangyan
Since this is my first coil gun,
and also my first project to do with electromagnetic propulsion, the
aim of this project is to construct a simple and working single stage
linear electromagnetic mass accelerator to better understand the
workings of this type of propulsion systems and to be a basis for my
further higher powered projects. This will be used to research
and demonstrate the principles of magnetic acceleration, and the
accelerator is to be kept as a test bay for different coil/projectile
combinations. The use of a single stage keeps design parameters
simpler and leaves more room for experimentation. Furthermore, this is
my first attempt at building one and therefore, the power would be
kept low. This coil gun would be built from a used disposable camera.
Cheap and easy! A high voltage sign is printed to warn others from
receiving a nasty shock!
