Introduction: .50 Cal Coil Gun

After building a small 6mm coil gun I decided it was time to upscale... To a .50cal...

Youtube video of it in action.


This would mean a dramaticaly larger capacitor bank and equally large solid state switches. Whilst under construction I was approached by a Professor in the Engineering Department asking whether I could adapt it for use as a demonstration piece on electromagnetic acceleration. It only involved a few safety measures so I agreed and they gave me funding for components. The big buy was going to be a high current and voltage solid state switch. Luckily a Mitsubishi CM400HU-24F IGBT was supplied by a member of staff in the department who works on the power systems in trains.

Step 1: The Theory

A coil gun works on the principle of electromagnetic attraction. The coil gun itself is akin to an air cored solenoid. A ferromagnetic armature is placed at the breach of the coil and is electromagnetically attracted towards the centre of the coil when a current is passed though the coil. When the armature reaches the centre of the coil it will start actively decelerating if the current is still passing through the coil as it is magnetically attracted to the midpoint of the coil. This means that the current pulse length needs to be of a finite length in order for the armature to be accelerated up to the centre of the coil and not ‘sucked back’ as it tries to leave the coil via the other end. This is more specifically a ‘reluctance coil gun’, a diagram is shown below.

This is the biggest disadvantage to coil guns, the current pulse length needs to be controlled in order to cut the power when the armature reaches the middle of the coil.

The second largest challenge to overcome with coil guns is delivering the electricity as quickly as possible. It stands to reason that the more energy you can put onto the coil gun, the more energy will be transferred into kinetic energy in the armature.

The main losses in this system are the eddy currents in the flyway tube and the projectile/armature, these can be minimised by slotting the flyway tube or using a non-conductive material. The projectile must be ferromagnetic thus this means that limiting eddy currents cannot be achieved by using a non-conductive material. The best solution to this is to use a powdered Iron in epoxy resin matrix. Although this improves initial efficiency it also removes the ability for the gun to be operated as an ‘inductance coil gun’.
 

Step 2: Things to Consider When Designing

Projectiles
I've done a separate Instructable on Projectile Design since it is such a big section.

Coil Length
The longer the coil is the more time it has to drag the projectile to the centre and the more wraps of wire can be fitted into the solenoid increasing magnetic flux density. The longer the piece of wire the coil is made of and the higher the inductance of the coil the higher the reluctance of the coil is so the longer the current pulse length will be. This means that the rate of change of current is lower and so will not reach as high a peak value. Since the current effects the magnetic field density a high current is desirable so the coil should be tuned so that it makes the strongest magnetic field in the time available.
The coil length is directly linked to the projectile length as they should be roughly equal as mentioned previously.

Number of layers in the coil
More layers mean a stronger magnetic field but it also means higher impedance and so a longer pulse length. If the pulse length is too long then the projectile will experience ”suck back” and have a lower exit velocity, optical triggering can be used to solve this problem.
Too many layers will mean that the magnetic field of the outer layers adds no strength the magnetic flux density in the centre where the projectile is and so the energy is wasted. It also means that the pulse length is unnecessarily long so the current will not rise as sharply as otherwise possible.

Thickness of coil wire
Thicker wire means lower impedance so a faster pulse length and higher peak current. This means less wraps in the coil per unit area so the flux density is potentially reduced if the current isn’t significantly increased by the lower impedance. If the wire is too thin it will have too high a resistance and get unnecessarily hot. In extreme cases it can burn out on firing.

Pulse Length
The pulse length should be exactly the same length as the amount of time it takes to pull the projectile from the breach to the centre of the coil and return to zero. The pulse length is affected by a myriad of variables including, capacitor voltage, capacitor capacity, circuit resistance, and coil inductance which varies dynamically during use as there is initially an air core which is soon replaced with an iron core as the projectile slides in not to mention depending on how many turns, layers and what gauge of wire is used.

This problem is solved by fixing as many variables as possible such as capacitor voltage and size, projectile dimensions which in turn fix the coil length and internal diameter. Then the remaining variables are varied until the optimal combination is found. The remaining variables are most importantly wire gauge and number of layers. Assuming a suitable switch can be used the wire gauge is usually the largest available.

Switch bounce/resistance
Mechanical switches can arc and bounce which lengthens the pulse and lowers the average flux density experienced in the tube during firing. This is overcome by the use of solid state switches such as SCR’s, MOSFET’s or IGBT’s which experience none of the arcing issues. They are not perfect solutions though as they have several flaws such as requiring a switching current/voltage to work and SCR’s cannot be switched off until the source-drain current drops below zero so require “v-switching”. V-switching is where a second SCR and cap bank of the same or higher voltage is discharged through the first SCR dropping the voltage below zero and switching the switch off.

MOSFET’s are generally quite low power so are of no use to coil guns of a decent scale and a suitable one can be expensive but a solution is to use a bank of them is parallel to spread the current over several less expensive devises. IGBT’s are much better solutions as they can be switched on and off at will and can handle far higher power than MOSFET’s. It is also important that the solid state switch can operate fast enough to turn the device on and off in the desired time frame, Most IGBT’s are capable of this as well.

Capacitor Voltage
The higher the capacitor voltage the higher the projectile velocity since the stored energy in a capacitor is equal to half the capacitance multiplied by the voltage squared as long as the switching capabilities are there then this is one of the more favourable variables to choose to increase as each extra volt makes a big difference.

Capacitor Capacitance
The higher the capacitance the larger the volume of stored energy in line with:
Energy stored in a capacitor=1/2 CV^2

Coil Flux Linkage (external Iron)
Adding an external iron shell to the coil can improve the flux linkage between the coil and the projectile but care must be taken to eliminate Eddie current losses. A powdered iron matrix or ceramic ferrite is therefore the best option. The External iron must not have too much mass as the extra iron material will slow the magnetic flux build up and the coil gun may not saturate as not all of the ferrous material is magnetised which means it is dead weight and just slows the flux density increase rate. This would mean that the magnetic flux would not increase as rapidly and not reach as high peak value. Too little ferrous material means it is potentially wasting the magnetic flux available.

The External iron must therefore be optimised so that it does not saturate and yet there is enough to enhance the magnetic flux density. It will affect the inductance of the coil and so the current pulse length so the coil may need to be of a slightly different shape to gain optimal performance.

Minimise connecting wire length
All connecting wires between the coil and the capacitors should be as short and thick as possible to reduce resistive losses and inductance.
 

Step 3: The Design

Capacitor bank size
A bank of 40 330v photoflash capacitors of 100uF capacity where used giving a total energy capacity of 217.8J:
E=1/2 CV^2
E=1/2*4000x10^(-6)*330^2
E=217.8J

Switching
Only solid state switches would work for this project as any other switches would arc. I was supplied with an IGBT capable of handling up to 1200V and 800A Peak and a maximum full switching on and off time of 1300ns. This is fast enough and can handle far more volts than needed but the current is only just enough. It switches at up to +/- 20v.

Charging
A 1.5v to 400 volt inverter has been included in the enclosure to enable the device to be charged of AA batteries but this would be slow and would use several batteries per shot. The main charging comes from half rectified mains using a light bulb as a charging resistor to give non-linear resistance through the charge cycle. UK mains electricity is 240v RMS, which when half wave rectified using a diode comes out at 336v. My capacitors charge up to 330 volts so 336 is perfect and mains will allow me to charge the bank cheaply and quickly when compared to the battery solution. A resistor was placed across the capacitor bank to slowly discharge it to make sure it is always left uncharged.

Voltage Monitoring 
A simple voltmeter has been mounted to the enclosure so that the voltage on the capacitor bank can be monitored in real time to check the charge state and double check prevention of overcharging.

Projectile dimensions
Through trial and error and parameter sweeps I found the optimum set up for several different diameters of projectile. The important results are below; all were limited to roughly 800Amps so my IGBT could handle the current.

6mm Diameter
The standard 6mm coil gun with the predetermined limits from above would give a rough maximum of 33.5m/s and 3.6J kinetic energy on 15 layers of 14AWG 30mm length. The capacitor bank was so large this was evidently too much power to dump into such a small projectile in one stage. The projectile size was too small and a larger projectile was needed. The simulation graph is below

10mm Projectile
Using a 10mm projectile it was found that a 40mm length coil would be best using 10 layers of wire and producing 25.4m/s but a more reasonable 7.6J of kinetic energy.

12mm Projectile
Using a 12mm projectile an optimum length of 45mm was found with 9 layers of 14AWG. This gave a velocity of 22.7m/s and a kinetic energy of 9.9J with a peak current of 811Amps.

15mm Projectile
Using a 15mm projectile an optimum set up was found to be 7 layers of 50mm length 14AWG. This gave a velocity of 16.65m/s and a kinetic energy of 9.15J. This was less than the 12mm so the 12mm was used.





Step 4: Methods of Data Collection

Optical gates
Two light gates are put a set distance apart and electronics are used to measure the time between the two gates being passed and the velocity is displayed on an LED segment display. I have the circuit diagrams and plans for the device but did not have the time to construct it.

Ballistic pendulum
A mass of deformable material is suspended from a fixed length beam; the projectile is fired at the pendulum and sticks into the mass. The kinetic energy of the projectile is transmitted into the pendulum and the maximum displacement measured. Then the kinetic energy of the projectile can be calculated from the vertical displacement as Work done=dh*g*m where dh is the change in height, g is the gravitational constant and m is the combined mass of the pendulum and the projectile.

A computer mouse can also be used by attaching the pendulum arm to the scroll wheel and then by measuring the time between each interval on the wheel and the length of the arm the velocity of the target and hence projectile can be calculated.

Vertical ascent
The coil gun is fired vertically and the maximum displacement measured usually by a camera. Using VUSAT equations the initial velocity can be calculated since the acceleration under gravity is 9.81m/s

High speed camera
The coil gun is fired against a back drop with 10cm intervals on it. The shot is recorded on the high speed camera and the time taken for the projectile to travel the 10cm distance is measured so the velocity can be calculated.

Horizontal VUSAT
The coil gun is fired from an arbitrary set vertical displacement of 1m for example. A soft foam target is set up several meters away and from the indent in the foam where the projectile hit the target the final vertical displacement can be measured. From the change in displacement the flight time can be calculated because acceleration under gravity is 9.81m/s then the distance from coil gun to target can be divided by the flight time to get the velocity. This is the method I used to take measurements for my 73J coil gun.

Sound gates
The coil gun is fired through two pieces of paper one meter apart with a microphone equidistant from each. The sound file is recorded and analysed. From the time between the two noises the time to travel one meter and hence the velocity can be measured. 
This is the method I used to measure the velocity of my 217J coil gun.







Step 5: Testing

Results

YouTube Video of it in action: http://www.youtube.com/watch?v=MYf_fSE3ZUo

From the 217J coil gun I only got one set of results due to time constrains and health and safety issues. Using the Audio Chronograph I got the following results:

first pulse 0.02
second pulse 0.07
time between hits 0.05
distance from target to mic 1
time delay from taget 0.002939
actual flight time 0.047061
Velocity (m/s) 21.24887

The coil gun was predicted to shoot at 22.7m/s. The actual velocity of this particular shot was 21.25m/s. Launch position and slight variations in capacitor bank voltage can have a larger effect than this on velocities. Added to this the program I used to simulate the coil gun and estimate its effectiveness does not take into account things such as friction in the barrel and air resistance and hence tends to overestimate performance slightly. With these considerations taken into account the mathematical modelling can be seen to be surprisingly accurate.



Comments

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LabRatMatt made it!(author)2017-01-04

Mine isn't nearly as powerful, but I made it almost completely out of scrap: https://www.instructables.com/id/Camera-Capacitor-C...

I've been thinking about building a much more powerful version, but that will have to wait until I have the time and resources to do it right.

Im

handheld coil gun frame.JPGIMG_1193.JPG
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kschmidt2 made it!(author)2013-08-12

so if I had a way to get 20kv to peak for 50 microseconds, what do you think the result would be going through a coil? too quick is what I'm thinking, I'm also thinking that the coil would burn out unless it was about 3 mm thick. What are your thoughts on this?

This is purely theoretical, I'm just really interested in knowing what would happen.

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LetsBuildOne made it!(author)2016-01-15

There are too many variables missing to give a succinct answer. I'd need capacitance, or max current at least. Why 50uS? surely the pulse length is governed by the discharge, which has more to do with the capacitance and current. Unless it's a battery bank, which has a current limit. If you have 23kA to go with your 20kV, then we could get 140m/s out of it, 214J KE. Pulse length is 900uS though.

I'm struggling to get the pulse down to 50uS. The system is under damped. Peak Current at 200J bank, is only 41A. 6.8m/s, 0.5J KE.

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kschmidt2 made it!(author)2016-01-26

This is so specific because I was looking at using a motorbike magnito and CDI ignition system for a power source, they peak at 20kv for 50 microseconds, but they're really, really low amperage, so it wouldn't work, I'm still going to try it for a rail gun though, just to see how it goes. If it works it'd be an easy way to make a rapid fire sort of device due to the speed at which it can discharge.

Thanks for the reply though.

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Speedmite made it!(author)2012-01-01

Would this work for a solid state switch if I had 120 of 330V 100uF capacitors? It would be like 3 of your bank in parallel.

http://search.digikey.com/us/en/products/FGA180N33ATDTU/FGA180N33ATDTU-ND/1916864

I would have to buy 15 IGBTs or so to put in parallel to handle the amps, and that would cost around 60 bucks, but I was wanting to build another coilgun/railgun, and though as fun as manually triggering it is, it looses a lot of bang. I built a railgun before, now Im thinking coilguns are more efficient. Eh, only difference is rails or coil, if I change my mind Its only gonna cost me like 5 bucks.

So about 15 in parallel wold work?

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LetsBuildOne made it!(author)2016-01-15

It comes out to about the same: 13J KE, 23m/s. but the current goes up to 1300A.

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ThinkDesignConstruct made it!(author)2015-01-30

can I get your simulator?

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LetsBuildOne made it!(author)2016-01-14

Yeah sure, Drop me an email at letsbuildone@live.co.uk

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LetsBuildOne made it!(author)2016-01-15

I've been told that email address may not be working. Try LetsBuildOne@gmail.com

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burdea made it!(author)2015-02-16

I tried to reach you at letsbuildone@live.co.uk address, but google could not deliver the message. Do you have another email address where I can ask for simulation software?

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LetsBuildOne made it!(author)2016-01-15

That's odd. I just tested it, and it seemed to be working. Try LetsBuildOne@gmail.com

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elizabeth.cain.7796 made it!(author)2015-03-12

how much gauss do those electromagnets reach to be effective

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LetsBuildOne made it!(author)2016-01-15

The electromagnet maximum flux density, is 45900 Gauss for this coil gun.

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LetsBuildOne made it!(author)2016-01-15

The electromagnet maximum flux density, is 45900 Gauss for this coil gun.

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hulkbuild made it!(author)2016-01-12

Bloody good job, mate! The theory is very helpful. Like anything, there aren't really rules to making coil guns, but you did a good job of laying out some of the guidelines. I am thinking of making a coil gun, but am unwilling to work with high voltages. I am hoping that there is a way to make a gun using supercapacitors, which use low voltage but have high capacitance. The resistance of the coil would have to be low, though, or I won't be able to push much current through it with a low voltage.

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LetsBuildOne made it!(author)2016-01-15

Say you use a bank of 10F, 2.5V caps. Charge up to 50v. That's 12500J energy. Over 50 times more than the .50 Cal. This bank, shooting 6mm projectiles, would struggle to break 20m/s, 0.7J KE. This one has 13J KE.

Yes you can make a coil gun using low voltage super caps. But don't expect anything like the power that the .50 Cal delivers. It will be closer to the 6mm coil gun.

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MainAvel made it!(author)2014-06-18

And what do I do, if I don't want a lightbulb?

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LetsBuildOne made it!(author)2016-01-14

Use any other 240vAC device of a <100w power. I saw one that used Neon tubes. They're higher power though, so it charged faster.

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absolute+zero made it!(author)2013-09-20

Sorry if you mentioned this and I didn't see it, you have a very good article here. Where should your projectile be at its still position? I've only ever used round projectiles which were placed just outside the edge of the coil.

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LetsBuildOne made it!(author)2016-01-14

It depends on many factors. As a general rule, they should be on the breach of the coil. That is, fully outside, but butt up against it's opening.

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LukeM11 made it!(author)2015-03-30

I've been wondering this for a while

Has anyone had the guts to build a quench gun, a gauss rifle but with superconductive magnets, aside from military or anything with large funding. I have no idea if it is possible on many levels but if you made the coil out of lead, put it in the superconductive state, and then used aerogel to insulate it.

As I said I have no idea if this is possible but it would be really cool to see.

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ausieking made it!(author)2013-05-27

what is the charge time to fire a projectile

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LetsBuildOne made it!(author)2013-05-30

about 45 seconds.

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Wizzup made it!(author)2012-12-15

Is that simulator available to use somewhere for everyone? I would like to use it to design my coilguns coil better. If not, any chance you could do the sim with my current coils parameters?

Cap bank:
3300uF 370V = ~226J
Switching is made with a big SCR

Coil:
1mm thick magnet wire
It is wrapped on a 16mm outer diameter plastic pipe
3 layers, the whole coils outer diameter is 23mm
41mm long

Projectile:
Material is iron, it is 28mm long, 10mm diameter
Mass 17 grams

This is my first coil for this so i would like to know how it performs, i think i would get much more speed with more coil layers and shortening the coil a bit but i would like to know how the current one does before making another. Also all suggestions for the coil design are very welcome.

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LetsBuildOne made it!(author)2012-12-28

Yes, I would be happy to e-mail you the simulator. Just drop me an e-mail at letsbuildone@live.co.uk asking for it and I'll send you the .zip!

As for optimizing your coil gun:
As a guide my coil gun is 217J and KE is about 10J @ just over 20m/s. I optimized for maximum kinetic energy at the limit of 800 Amps peak that my switch could handle

Your design currently puts out a predicted 2.2J at 16.7m/s

First you tube is unacceptably thick walled. The magnetic field strength reduces with the square of the distance to reducing your 16mm tube to a 12mm tube results in:
2.85J at 18.7m/s, If you managed a 10.1mm coil by forming the coil in epoxy you could improve that to 3.12J at 19.59m/s. I'll stick with 12mm for subsequent optimization though.

The coil isn't big enough either and it is discharging too quickly. Increasing the number of layers from 3-7 increases the velocity to 7.37J KE at 30.1m/s.

Further than this I will need to know what the peak current your switch can handle is and also if you are optimizing for velocity or kinetic energy.

LBO

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Tristan23 made it!(author)2012-10-30

i want to know are you using a multi meter

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LetsBuildOne made it!(author)2012-10-30

Yes

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nonobadog made it!(author)2012-05-13

You could get much better performance from a slingshot. How can one increase the performance?

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LetsBuildOne made it!(author)2012-05-13

If your aim is to do damage at range then a slingshot would be a lot cheaper, easier, and effective. A slingshot can't accelerate a projectile using electricity and magnetism without physically touching the projectile and the acceleration will never be any where near as fast, coil guns also have no upper limit to the speed to which you can accelerate the projectile and hence how powerful it can be. Maybe the speed of light... Tacheons though... and that particle they found at cern maybe...

You can make a coilgun more powerful by putting more energy in. That isn't quite as easy as it sounds though. You could increase the length of your projectile, the coil, and increase the size of your Cap bank in accordance with this. You can also place a secondary coil after the first to further accelerate the projectile when you reach the limit of what can be done with one coil. You can then keep stacking coils but each coil adds much less power than the one preceding it so it's diminishing returns.

The US military are researching them for use in long range weapons for ship but the big problem is that when they try and fire it, the recoil would sink the ship! They were also considered in WW2 for shooting down aircraft as the projectiles are cheaper and easier to produce. All it needs is electricity to fire them and it's rate of fire is almost unlimited, storage of projectiles is less dangerous because there are no explosives involved.

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H20 made it!(author)2011-12-18

My science fair project is based around coil guns, but I don't know how to measure the velocity. I've looked at Youtube videos and have seen the phototransistor method, but I'm not sure if the projectile will go fast enough. Is it OK to place to PT's 1 cm apart?

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LetsBuildOne made it!(author)2011-12-19

1cm apart wouldn't give you an incredibly accurate measurement. The further apart the better. Also the PT's will probably involve some fancy circuits to work out the velocity or the use of an oscilloscope preferably with computer input.

The best method I have found is to stretch out two pieces of paper one meter part and put a microphone in the middle of them (out of the projectile flight path of course). Record the sound on your computer as you fire the coil gun and then use audio editing software to measure the time between the two bangs as the projectile hits each sheet.

Alternatively you can put it 1m off the ground and shoot it horizontally into sand. You can see then measure to the imprint where it landed and use SUVAT equations to calculate the initial velocity.

Finally you could video it shooting in front of a background of equally spaced black and white strips and measure how many it goes over per unit time or how much time it take for it to travel over say ten of 1cm width.

Does this help?

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H20 made it!(author)2011-12-19

if I were to use phototransistors I would find the velocity using Audacity. I have thought about using slow-motion footage but don't have a slow-mo camera or knowledge of any software that could slow the footage down. Do know of any software?

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LetsBuildOne made it!(author)2011-12-20

How would you get the phototransistor signal into the computer in audio format for audacity to analyse? I have some phototransistors for just this purpose, if you could tell me how I'd be very great-full!

I have done the camera approach and a standard camera films at around 25frames per second so over a one meter length it could measure up to 25m/s. I found that at 21m/s it was inaccurate as the projectile was blurred from the lengthy exposure time of my camera. You don't need to slow it down. You need to see it frame by frame with the frame time stamp to 100ths of a second. I used a free trial of Adobe's software available from their website. These others are also available:
http://www.desktop-video-guide.com/top-5-free-video-editing-software-review.html

As long as you can guarantee that the projectile will pass through your two light gates and you can get that signal into the computer then that will be your most accurate and easy option. I would posticulate that the PT signal would be easier to analyse than the microphone method as it will have less noise and a clearer step change as the beam is broken.

Most sound cards run at 48kHz so over 1cm you could measure up to 480m/s though accuracy would be much better at velocities closer to half that.

You should also make your measurements as large as possible as if you can only place your PT's accurate to +/-1mm then you have 4mm of uncertainty in the PT's position which is 40% of the measure so your velocity is effectively an estimate. If it were 100mm then it would be 4%, 1000mm 0.4%uncertainty, you get the idea. Also it means that the time would be longer between the gates so you could measure that more accurately in the software.


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st5k made it!(author)2011-12-17

ok.... i have been working on building a coilgun for a while now and i wanted to pick your brain a little. first off what im working with are 10 450v 1000uf caps, and i was using a homemade static tranfer switch. essentially 3 bolts in a small box with a 20k neg ion gen, worked pretty good too. anyway, should i hook these caps up in series or parallel? i had them in parallel but i wasnt getting the oomph i was looking for. that could have been because of my coil too im not sure, it was pretty crappy not gonna lie. i cant remember the gauge of the wire, i wanna say it was 16. the coil was approx 4 inches long with 3 layers, and i was using a plastic tube with a 5/16 bolt as a projectile. also what should be used as a charging system? i was using a flyback transformer, but was a bit slow. i would love any sort of input u can provide.

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LetsBuildOne made it!(author)2011-12-19

You want to hook your caps up in parallel. I doubt you have a 4.5kv supply hanging around to charge the series bank.

At 450v you could use full wave rectified mains maybe from a 12v-240v inverter passed in series through a neon tube on the AC side of the bridge. This would only charge to around 340v though. a little short of your 450v capability. You could use two in series to get 680v then use a charge regulator to limit it to 450v. Or simply watch the voltage across the caps and cut it before it goes over 450v.

Your coil and your projectiles are undoubtedly what are costing you performance. Firstly your 5/16 bolt has a thread which will mess up your flux linkage from the coil to the projectile and effectively introduces an air gap. It will also have more friction and air resistance. You want a smooth non-electrically conductive, ferro-magnetic projectile with flat ends. you can buy ferrite cores off ebay in short lengths.

Your coil will also be stunting its performance. I don't have my simulator on this computer so I can't tell you what coil you want right now but the dimensions of yours seems wrong to me. Firstly the L/D ratio is too high. Your coil should be the same length as your projectile and your projectile should be roughly 5-9 times as long as it is diameter. 4"=100mm is too long. 5/16"=7.9mm so 40-72mm (2"-3") is about right.

At that much power you also want thicker wire, 14AWG or thicker. I can't be sure without checking the maths but three layers seems to few to me. My experience suggests that somewhere around double that would be better.

Are you going for raw power, as in projectile kinetic energy, Piercing power, as in pressure per unit area, or projectile velocity? Each is a different coil and projectile. High velocity wants a light weight projectile and a longer coil with fewer layers. Raw power means you want a large diameter heavy projectile with a short fat coil. Your talking over a 0.50cal. For piercing power there is a compromise to be drawn between diameter which you want thinner, and weight which you want higher but you can't increase the length too much...

Finally it sounds like your coil is badly formed. your plastic tube may be too thick, your projectile may not be a snug enough fit in the barrel or too tight and stick. Your coil should have end plates too that the coil is formed between so it is nice and square in cross section. You should coil it nice and tight and glue each layer in place, one at a time. Try to minimise the gap between the coil and the projectile. The easiest way to do this is to use your projectile as the coil form. just wrap a piece of paper or plastic around it first, one thin layer.

To be honest I know nothing about Static Transfer Switches. This could be inefficient and waste energy compared to solid state alternatives. I appreciate that as these voltage and currents they can be rather expensive though. I'm using a pneumatically actuated spark gap switch with two ali blocks and a copper peg with a morse taper submerged in mineral oil. No current and voltage limits in my range and loses are minimal.

If you want any further help just ask :)

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newwarhammer2 made it!(author)2011-09-22

could i use 1 x120,000 Microfarad capacitor at 16 volts?

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LetsBuildOne made it!(author)2011-09-22

Yes, you could. Don't be expecting amazing results though as the energy stored in a capacitor is 1/2cv^2 so my 4000uF bank at 330v would give 217Joules, I charge it to closer to 400v, that's 320J. Your bank would be 0.96J Therefore less than 0.5% as powerful as this one. This is 13J KE so yours would be 0.06J KE roughly speaking. To put this in perspective, a powerful airsoft gun is 1J. Personally I'd go to your local camera shot and get soldering!

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spark+master made it!(author)2011-09-08

how hot does the projectile get?

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LetsBuildOne made it!(author)2011-09-15

Not noticeably warmer. Once, after several shots of the same projectile in rapid succession I noticed it was slightly over ambient .

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spark+master made it!(author)2011-09-15

could use thin walled capped iron pipe and add a tail and fins like olde tyme grenadiers did, accuracy would be improved. This gizmo is quite a nice lawsuit waiting to happen I must say , I want one! Then again my land is too small, and the rabbits run as it is, stttiiiillll ....... Wosted wabbits fweshly wacked in the yard.... Bacon wrapped of course....

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LetsBuildOne made it!(author)2011-09-15

As I explain in my instructable on projectiles, You don't want circular conductive paths in the projectile as they allow eddy currents to form and waste energy. The volume/mass of ferro-magnetic material in the projectile is also important as you want enough so that it fully saturates in the magnetic field but not so much that it doesn't fully saturate and you waste energy accelerating dead mass. Essentially, the size and density of the projectile need to be balanced with the inductance to get optimal performance. If you read this instructable and the one on projectiles you should understand what affects coil gun performance. If that still leaves you with questions or you want clarification I will be more than happy to fill in the blanks :)

author
spark+master made it!(author)2011-09-16

Shucks, I was hoping for a hollow projectile. Since you like high voltage check out

http://205.243.100.155/frames/shrinkergallery.html

Bert is a very cool maker of strange things , (like the magnetic gun), when he makes his items he will erase your cred cards magnetic strips and the end result is a hoot.

thanks fer th efeed back

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spark+master made it!(author)2011-09-08

awesome, how heavy are the projectiles, are they ball bearings, pieces of iron pipe?

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LetsBuildOne made it!(author)2011-09-15

I've writen an instructable on this subject: https://www.instructables.com/id/Coil-Gun-Projectiles/

Getting to the point: They are variations on a 55mm long, 13mm diameter solid soft iron bar. They weigh from a little over 40g.

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spark+master made it!(author)2011-09-15

Almost a 2 ounce weight I will check out your other instructable

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XOIIO made it!(author)2011-08-09

Can you give me any help making a faster charger for my coil gun? I have 14 330v capacitors rigged up for testing, but I have 145 cameras to take apart and scrap from. Can you give step-by-step instructions on how you ade the charger for your capacitor bank?

author
LetsBuildOne made it!(author)2011-08-11

Yes I can, I am however currently in Southport celebrating my birthday and as such have none of my stuff with me. Having said that I'll see what I can do now.

Right, you have a couple of options.

First you could use full or half rectified mains. The simplest way to do this is to use a diode from the live followed by a mains rated switch and then a light bulb fitting with a 20W light bulb in it. In the UK you'll get just under 340v DC out. In the US if the mains is 120v then you'll get 170V which isn't a lot of use to you. If you use this method you need to use a voltmeter to monitor the charge level and make sure you don't overcharge them. Also put a couple of mega ohm resistor across the capacitor bank to make sure it can't be left charged and will naturally discharge itself.

You could use 12v DC to 240v AC inverter to source your mains. they're available on the net for about £20 and will run off any 12v source though a decent size lead acid or gel cell would be recommended.

If either of the above options are used then a diode bridge could be used to double the charge rate with full wave instead of half wave rectification..

The other way of doing it is to use a step up buck boost converter but they are a lot more complex to make and explain here.

You could also just link up several camera flash chargers in parallel or add a second 1.5v battery. This is a good way to blow up circuits though so keep a few spares. Camera flash chargers aren't designed for that kind of punishment and don't usually last that long.

Hope this helps, If you want more help then let me know and I'll draw you some circuit diagrams when I get home.

author
XOIIO made it!(author)2011-08-11

Well I do have 137 circuits from all the cameras I took apart, my current charger is two of the worlds smallest shocker circuits because they have more oomph. but they do take a few minutes to charge it, and I'm looking for something much faster. I could use a car inverter with a power supply, and that seems to be the easiest option aside from trying to replicate the camera circuit with a larger transformer, but I would need someones help sizing up the resistors, and the transistor might fry.

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tazerboy made it!(author)2011-04-30

i am having troubles with switching my gun please help, i have a two 450volt
470uf capacitor wired in parallel. and i couldn't find a solid state switch that will
suit it. please help

author
Maverick+A. made it!(author)2011-04-02

Have you tested the maximum effective range of this coilgun?
(If you have tested the range; how long is the effective range?)

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Bio: I build stuff because it isn't available to buy, or is too expensive, or the ones you can buy don't do what I ... More »
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