Presentation on theme: "Introduction For Coil gun"— Presentation transcript:
1Introduction For Coil gun -Barry's Coilgun Design
2What is a coilgun or gauss gun? It accelerates a piece of iron or steel down a tube. The tube runs through a series of electromagnetic coils (like solenoids).
3Introduction Solenoid Physics Magnetic Field Force From Magnetism Magnetic MaterialsSolenoid PhysicsMagnetic FieldForce From Magnetism＊ Force Is the Gradient of Potential Energy＊ The potential energy in a magnetic field is Saturation＊ The B-H curve here illustrates the effect of magneticsaturation. It shows the effect of applying an externalmagnetic field to unmagnetized iron.
4Introduction Capacitors Energy Storage ＊The charge or quantity of electricity that can be held in the electric fieldbetween the capacitor plates is proportional to the applied voltage and to thecapacitance of the capacitor: Q = C * V whereQ = charge in coloumbsC = capacitance in faradsV = voltage in volts＊The energy stored in a capacitor is also a function of voltage andcapacitance: W = V2 * C / 2 whereW = energy in joules (watt-seconds)
5Capacitor Charge and Discharge τ0.37I0I0=V0/RtI0=ε/Rτ=RCcεq0.63cεCapacitor Charge q-t plotCapacitor Charge I-t plotqτ0.37cεcεt0.37I0II0=ε/RCapacitor Discharge q-t plotCapacitor Discharge I-t plotNational taiwan normal university
6Introduction Inductors (Coilgun) ＊The symbol and defining equation for an inductor is,where L is called the inductance.Damped Oscillator (RLC)＊The voltage V and current I as a function of time
7Introduction Critical Damping ＊When R2C2-4LC is positive, then α and β are realnumbers and the oscillator is over-damped. Thecircuit does not show oscillation.＊When R2C2-4LC is negative, then α and β areimaginary numbers and the oscillations are under-damped. The circuit responds witha sine wave in an exponential decay envelope.＊When R2C2-4LC is zero, then α and β are zeroand oscillations are critically damped. Thecircuit response shows a narrow peak followedby an exponential decay.
8Introduction Measuring Coilgun Speed ＊ Horizontal Ballistic Speed Trap If you fire the coilgun horizontally off a table, and measure the distance to where it lands, and the height it fell, then you have enough information to calculate the speed.＊ speed = d * SQRT(g / 2h) 1where d is horizontal distance in feet (or meters) and h is vertical distance in feet (or meters) and SQRT is the square root function
9Barry's Coilgun (1) Result: Position Dist (x) Muzzle Speed 18.6mm ＊The exit speed is quite sensitive to the projectile's precise starting position. It takes only a few millimeters further in or out to gain or loose significant speed. This graph shows the measured speed compared to how far the projectile was inserted into the coil.Dist (x)Muzzle Speed18.6mm 4.46 m/s20.44.6721.55.00 m/s22.54.7324.04.2626.83.7328.51.25
10Barry's Coilgun (1) Result: Turns ＊ The timing is entirely controlled by the inductance and capacitance. The coil should be wound with taps at various layers, so you can choose the number of turns and therefore the inductance.LayersResult14strong snap to middle of coil 12strong snap to middle of coil108strong snap, fell out wrong end61.39 m/s forward44.41 m/s25.00 m/s
12Barry's Coilgun (1) Results - External Iron Conclusions ＊This coilgun was built with iron washers at each end to help focus the magneticfield.ConclusionsThis coilgun works best with no external iron. With Iron Without Iron4.78 m/s 5.93 m/s
13Barry's Coilgun (1) Result: Tube Conclusions Brass Tube Plastic Tube ＊Does the material of the firing tube have any effect?＊In running this test, I discovered the plastic firing tube made a dramatic 24% improvement in exit speed. This tells us the eddy currents are very significant! We can expect the energy losses in eddy currents to get much higher as we move to shorter firing times, since eddy currents increase with frequency.Conclusions＊This coilgun worked 24% better with a plastic non-conductive firing tube. This was the single biggest performance gain of any changes I've tried! The plastic tube was inexpensive, but other materials and construction techniques should also produce the same benefit.Brass Tube Plastic Tube4.78 m/s 5.93 m/s
14Barry's Coilgun (1) Result: Tube ＊Eddy Currents The large and rapid flux changes will induce surface currents in the conductive projectile. Eddy currents always act against the applied magnetic field, reducing the absorbed kinetic energy.Eddy currents are an important effect; a much earlier coilgun found a 24% reduction in velocity due to eddy currents in a brass firing tube. Since then, we have only used non-conductive firing tubes such as the plastic ones in this coilgun.
15Barry's Coilgun (1) Result: Voltage Conclusions - Volts30mm Speed45mm Speed 5v 010v12v1.56 m/s 0.07 m/s 15v3.403.0620v5.245.0025v6.015.4230v6.405.9035v6.616.8040v6.747.0945v6.917.3450v6.967.6055v6.757.8560v6.267.7164v5.917.51Conclusions -Notice the sharp knee around 20 to 30 volts.Then only 10% gain is achieved when the voltageis doubled to 60 volts. A reasonable tuning strategy isto gradually increase the voltage until this knee is identified.Further voltage increases will stress the circuitry withoutproviding significant benefits.
16Barry's Coilgun (2) Projectiles Result: Coil of 97 Turns (velocity) ACDFPotential energy (joules)Charge (volts)Velocity (m/s)0.6 J10 v1.316-2.4202.9193.3195.4304.2925.6095.9526.5249.6405.5516.1816.9257.55415.0506.1247.1547.8407.89833.8758.01260.01008.871
17Barry's Coilgun (2) Result: Coil of 97 Turns (Efficiency) Projectile: ACDFPotential energy (joules)Charge (volts)Efficiency (%)0.6 J10 v0.6 %-2.4126.96.36.19900.70.60.39.6400.40.215.05033.87560.0100
19Barry's Coilgun (2) Result: Coil of 84 Turns (velocity) Projectile: A ACDEFGPotential energy (joules)Charge (volts)Velocity (m/s)0.6 J10 v0.0-2.4202.2895.4303.9499.6405.49415.0506.5818.2418.8718.9859.10010.874
20Barry's Coilgun (2) Result: Coil of 84Turns (Efficiency) Projectile: A ACDEFGPotential energy (joules)Charge (volts)Efficiency (%)0.6 J10 v0.0 %-2.4200.55.4300.69.6400.715.0500.40.2
21Finite Element Magnetics you can analyze coilguns without building them and study effects that you can't build, by using finite element analysis (FEA) software and simulate your coilgun.
22Finite Element Magnetics FEM Models - Hollow Cylinder Projectile＊The graphs for seven different projectiles are practically on top of one another. Therefore, the force per unit of mass does not depend on the inside radius of a hollow cylinder of iron.
23Finite Element Magnetics FEM Models - Projectile Length＊These results confirm therule-of-thumb that projectilesshould be about the same lengthas the coil.
24Finite Element Magnetics FEM Models - Coil Diameter＊ Smaller openings are better than bigger coils. In fact, smaller is always better. The graph proves that minimizing the air gap is important.＊ The energy transfer is not very sensitiveto coil opening size.
25Finite Element Magnetics FEM Models -Iron at Coil Entry＊ There is no dependence on work and washer thickness. The total kinetic energy is practically the same for every washer!Thickness (mm) Work (Joules)0.1204.80.6188.8.131.5204.72.12.6205.03.13.64.14.65.1
26Finite Element Magnetics FEM Models - Coil Current