IntroductionHave you ever wanted to use the forces of electromagnetism to launch a projectile? The coil gun is a relatively new invention compared to the older and different types built. A coil gun is a projectile accelerator consisting of one or more coils wrapped around a barrel and when you add electricity, these coils becomes electromagnets. Most coil guns will launch the projectile to high velocities but can be tweaked so it does not fire at high velocities. Another concept of the coil gun is called a Rail Gun. The rail-gun is strictly used in military due to the fast speed of the projectile at 8,600 km/h or 5343.
792mph (2.4 kilometers per second). The rail gun launches a 7 pound projectile at “hypersonic velocities”.
A coil gun works using electromagnets which is enameled copper wires wrapped around the barrel and has an electric current going through it. Electromagnets are used daily from a doorbell, junk yards, and even to rock concerts. Some of the most important parts of this coil gun are the:Arduino uno, 3D printer, Stepper motor, IR Photo-diodes, IR LEDs, resistors, Fast Fuse and the batteries.
The 3D printer is a huge part in this project. The printer prints all of the base parts to the coil gun. The Arduino Uno is a microprocessor which drives the Nema 17 Stepper Motor to initiate the coin movement. The IR LEDs send out white light and when the coin passes under it, it blocks out the light from the IR Photo-Diode (receiver) causing the next coil to turn on.
The resistors are used to reduce current flow and divide voltages to the coils. Fast Fuses are used to increase safety to withstand surge currents when turned on/off. Electromagnets are simply coil wire wrapped around an iron or air core.
If it is wrapped around an air core then it is called a solenoid. When electricity is brought to the coil, it becomes energized thus making an electromagnet. Unlike the typical magnet, electromagnets are temporary and can be enabled or disabled through a switch or unplugging the wires from a power source.
There are two main types of electromagnets, AC and DC. DC is what makes this coil gun, DC is usually used to pick up or hold object while AC is used to demagnetize objects like TV screens. AC magnets changes flux density as the current goes through it. The polarity of this object will also change when the current changes every half cycle. The AC currents will actually be reduced compared against the DC magnet.
The importance to an electromagnet is the ability to control certain things within this including: flux density, polarity of the field, and even the shape of the field. The magnitude of the current flowing can be strengthened or weakened by the magnetic flux density, while the polarity is determined by which may the flow is going and the shape of the field is determined by the shape of the core which this coil is wrapped around. A major use of electromagnets are in transformers. Transformers are just two electromagnets coupled together with no isolation between the two. The electrical field can be determined by doing the following equation:E=F/q where “E” is the Electric field strength, “F” is Force and “Q” is the charge. According to Columbus Law, means adding more charge will lead to more electric force. Columbus Law says “The strength of the electric field of magnetism between two points charges, is directly proportional to the product of the magnitudes of charges and oppositely proportional to the distance between them.
” To find the strength of an electromagnet, use Magneto Motive Force (m.m.f)=IxN ampere turns. M.
M.F is the current, I is the flow through the coils, and N is number of turns within the coil. The strength is then determined by ampere turns. The more turns there are the greater the strength.2. Literature Review The first coil gun when it was fired, sounded even louder than a .22 round being fired. The launcher had 1 long continuous coil from start of the barrel to the end.
One long coil like this will in theory weaken the strength of the gun and with multiple stages, after each stage it would speed up therefore reaching higher velocities(if tuned right). The most recent coil gun was done at Rutgers School of Engineering and this project’s results reworded are increasing the layers would only increase the resistance of the coil, therefore weakening the current. The output voltage in this project was 230V leaving the object traveling between 15-20m/s. Launching the object through all 3 stages lead to 40-50m/s with a boost converter bringing the voltage to ~400V.
This device only launched 1 object due to the coils being discharged and having to charge them again and every object must be manually loaded into the solenoid (air core). The results of most coil guns are that the object launches farther and faster due to more voltage (over 4x the amount). 2.
1 Fictional Concept”Arc Reactors” are a fictional design introduced in “Iron Man” used to power things creating 8 gigajoules of power per second. While this not a real thing, it is relatable to a Multi-Isotope Radio-Decay cell. The closest thing to this is called the ITER Fusion Reactor.
The ITER will work by smashing two isotopes of hydrogen, deuterium, and tritium producing helium and a free neutron. When these are mashed together, the leftover mass is then converted to energy. The “Arc Reactor” is a circle likely because there are charged particles moving in a circular pattern being contained by a magnetic field produced by an electromagnet.
The magnetic fields can then curve these particles. The arc reactor used palladium which is known as a “cold” fusion. Palladium isotope Pd-103 produces Rh-104 using electron capture, which means one electron is taken in by the nucleus, which merges with a proton then creating a neutron and an energetic photon.2.2 3D Printer3D printers is a machine which can make a physical, 3D object by melting filament(plastic) into multiple layers on top of each other. The process starts by making or downloading the models on a computer or using a 3D scanner.
To prepare a model, it will need to be sliced which can usually happen through software like Cura on a PC. When it is sliced, the printer will then need to be calibrated by steps/mm. After the printer, the model can be moved from the PC to the printer by USB, data transfer cable(DTC) or Wi-Fi.
It uses some materials that are used in this project like the Arduino Uno and the Nema Stepper Motor. 3. Additional Background3.1 Overview The coil gun uses an electromagnetic field made by electrical current surging through a copper wire or a stage. This needs an object to pass between the coils in a barrel usually air or an iron core. Electromagnets are used in moving subway cars, some trains, doorbells, elevators and more. Information on coil guns come in pieces so to understand everything, research or explanations need to happen.
3.2 Railgun CharacteristicsCoil guns are relatively easy to carry around, because they do not need cords or compressors, possibly cheaper depending on what kind, lightweight, they can be more powerful than electric nail guns (if tuned right), do not need to oil any materials, and have no kickback like other “guns”. 3.3 Capacitors The reasonable choice is to choose a capacitor with higher voltage from the relationship of energy (W= ½ CV2).
The inductance will limit how fast the current will be at maximum. Resistances throughout the coil gun will also limit the current output. An aluminum electrolytic capacitor would be suitable for this project since these have the 2nd highest capacitance rating below super/ultra capacitors. 3.4 Size of the Coil The size of the coil depends on the length of the object it is shooting but still need to consider other variables like, turns ratio of the coil and number of layers. For it to be considered a stage, it will need at least 1 layer, in this case it is 12-14 layers. The gauge of the wire depends on how many layers we can fit in 1 stage.
3.4.1 TradeoffThe field is directly proportional to the number of turns and layers current.
If thinner wires are used, this will allow the magnetic field to be more powerful but as we increase the number of loops, the resistance also increases which will lead to a lower current. 3.5 Preece’s Equation W.H Preece studied the melting point of wires and made the following equation: I=AD¹?when A is the constant and D is the diameter of the wire in inches. If the copper is made of copper then we use I=12,277 A¹???When I is the fusing current in Amps and A is the cross sectional area of wire in square inches. 3.5.
1 Oderdonk’s Equation He also developed an equation to predict how long it takes for a wire to melt. I = current in AmpsA = cross sectional area in circular milsTm = melting temperature of the material in o CTa = ambient temperature, also in o Cs = time in seconds.3.5.
2 Summary Using these equations, the option of gauge wire depends on the person creating the project. In a coil gun, these equations do not matter because the current is going in and out so fast, it will not be able to melt the wire in time. Aside from these, another way for this analysis is to use more fundamental thermodynamic principles and Stefan-Blotzmann’s law to find the heat radiated. 3.6 ConverterIf a converter were to be used to step up the voltage. When the MOSFET is closed, the circuit would be complete forming a circuit to the ground. The terminal of the inductor connected to the battery will become negative to the terminal connected to the diode, successfully locking the two in series at a higher voltage which will proceed to release their combined energy into the capacitor as a transient waveform.
The diode will block the capacitor from discharging itself through the inductor, thus absorbing all the energy and allowing its voltage to steadily climb. The voltage across the inductor is:V?=L(di/dt)If the circuit is continuous then the inductor never touches 0. When the circuit is complete, the current from the battery cannot pass through the inductor which leaves the battery voltage as: VsubDC=L(di?/dt)=L(I?-I?/(t??’-0=L(?I/t??)I? is the initial current through the inductor prior to closing the switch (if any)I? is the current the inductor gains after closing the switch. T?? is the amount of time the switch remains open3.
7 Estimations for the converter The charging time could be assumed by PDC=VDCIDC=120.8=9.6WEC=(½)CV2=(½)(100)(450)2=10.125Jt=10.1259.61.
05sThe coil gun would never charge in 1.05s because the capacitors are not in the same bank. The voltage weakens as it loses energy so the capacitors may not be able to change its voltage. 3.8 Magnetic Field of a Solenoid dvectorH=(1/4pi)(idsxr)/(|r|3 D vectorH is the differential magnetic field intensity I is the magnitude of current passing through a cross sectional area of wire D vectorS is the differential vector in the direction of the current element through which I is flowing