Coilguns(Pulse Accelerators), like railguns(Linear Accelerators), use intense electromagnetic fields to propel objects at incredible velocities unreachable with modern gas driven weaponry (given enough stored energy of course). This coil gun is known as a reluctance coil gun. The coil uses its electromagnetic field to pull a ferromagnetic (magnetically affected) projectile, in this case a shaped steel round, toward its center. Ideally the current supporting the electromagnetic field will turn off when the projectile is in the center allowing the projectile to continue traveling down the barrel, out the gun, and to the target. Use a coil and a few batteries to understand the properties of this system better. Many coilguns incorporate multiple stages at lower energy levels as efficiency tends to die off as more Stored Energy is used for a single coil design. For more information go to step 5.
A basic coilgun operation diagram is included at the bottom.
'!!!!!!Learn More About Coilguns!!!!!!'
What is a relay?? (Elaboration on step 2)
How does it work?
A relay is a simple electromagnetic switch. It uses an electromagnet to pull two contacts of a separate circuit together, completing the circuit and allowing electricity to flow.
What is it used for?
A relay was originally used to allow a machine or computer to switch something on or off electronically. In this application it is used to switch the capacitors energy into the coil.
Why use it?
Relays allow more current to pass through them than regular push button switches, which normally weld together. You can use a very high rated toggle switch for this, but it is usually more expensive and larger than a relay of the same rating.
The Parts You Need Are:
From Radio Shack or Other Electronic Parts Dealer:
-20 or 22 AWG Hookup Wire (Buy both the solid and stranded)(Larger wire is better because it lowers the resistance in the system which increases the coil gun's efficiency)
-22-20 gauge Magnetic Wire (Depending on your coil preference;See step 2)(Radio Shack has a Package with 40 ft of this but I recommend buying it from a different store to save cost and to get at least 100 ft for a coil more than 7 layers thick)
-A Relay (Electronic Switch), Preferably 30 Amps or more (I got a 12VDC/30A SPST Automotive Relay from Radio Shack, but I would recommend a higher voltage and current rating)
-A Momentary Switch( I used the SPDT Switch with 3/4" Roller Lever from Radio Shack, but you can use a lower rated switch)
-An On/Off Switch(I used the DPDT Heavy-Duty Rocker Switch from Radio Shack but you can use a lower rated switch)
-Battery Packs (More than 2 2AA Holders and 1 9V Holder)(The more 2AA Battery Packs the better)( I would suggest getting a few 2 C Battery Holders as they provide substantially more power to the Charger, resulting in a MUCH faster charge time; be careful not to over load your chargers, see last step for safe charger to battery ratios.
From Other Places:
-Used Disposable Camera's (The More The Better as this is the gun's central component), You can get them by asking most photo places like in Walmart or CVS for used disposable camera's. Remember: it is for the batteries, not a gun...never
-Straws from Burger king or local chain(You May use another place's straws but the coil's inner diameter will differ; Of course if you choose a smaller straw a smaller projectile will go faster but not pack as big a punch, AKA momentum)Also,Smaller Straws may be used to place on the back of your projetile for stabilization, this works well.
-Large Nails (3/16 to 1/4 inch Diameter, or bring your straw to Home Depot to fit the right nail)
-A Bolt, two washers, and a nut. (The bolt needs to be the diameter of your straw and the washer needs to fit well and be as wide in diameter as possible)
-A spray paint "can gun" handle or other handle. (I got mine from Harbor Freight)
-Plexiglas, wood, or sheet metal(Optional for gun casing)
-Flux (Not necessary, but it does help)
-Super Glue/ Epoxy/ Hot Glue(Used for gun casing)
-Wire Stripper( A big help)
-Glue Gun( For outer casing)
-Screw Driver(Flat Head)( To get cameras apart and discharge capacitors)
Losing Drive To Build This? Check out The Videos
The PAR-1 video demonstrates the kinetic output of a 12 layer coil with a 470uF 400V(to 450V) capacitor, that's only 50 Joules!.
My Web Page: Future Experimental Systems
Go to see some coilgun and railgun projects of mine.
Finished a coilgun and want to share it? Post it Here: Coilgun Arsenal
Useful Electronic Goods Sites:
- Mouser Probably the best Distributor I've come across, vast selection of items, best pricing for a non-wholesale electronics site, and great navigation and organization.
- Goldmine Great prices on useful parts
- Digikey Good for hard to find parts.
- MPJA Great place to buy magnetic wire and LEDs
- Electrostore Large high voltage capacitors at cheap price and other high power components.
- Surplus of Nebraska Great prices on magnetic wire if bought in large quantities.
- Alltronics An OK surplus store
Step 1: Charger Circuits
Why connect chargers into a bank?
chargers themselves aren't very powerful, but when you connect them together in parallel like shown in the last picture you increase the possible power output that the chargers can handle. Increasing the number and size of your battery bank (at 3V) will increase the chargers output (to a point) until the chargers fry.
Connecting the chargers in Parallel OR Series?
The chargers are connected in parallel, i.e. each terminal is connected to the same terminal on the adjacent charger as shown in the picture diagram. I do not recommend putting the chargers in series, so don't worry about it.
Look and read the picture comments, the pictures show you how to make your chargers better than I can describe it.
First take your circuit and use a pair of wire clippers and cut off the section defined by the small transformer on the top right of the circuit (this includes a transistor and diode)(look at the picture for reference). Attach leads as defined in the picture.
Camera circuits are mostly inefficient i.e. 16% by my testing, if you want your gun to charge faster and with less battery drain check out my DC to DC HV Boost Converter.
The Mini Charger Idea credit Comes from Instructable member "245Tommy" who got it from you tube member "Halo2maniaccc". Thank You both
TEST EACH CHARGER INDIVIDUALLY BEFORE YOU PUT THEM INTO A BANK, some may be defective.
Remember: Flux/Rosin (Which is used to enhance solder's "stick") is important here. You do not need it, but it does help a lot.
Step 2: General Details
Connect the capacitors Via bare Solid wire and solder (Line up the negative with the negative!).
The capacitors should be rated 300 VDC to 900 VDC for best results.
The energy found in a capacitor can be calculated based on this formula:
1/2 x C x 1e-6 x V2
0.000005 x C x V x V
Where C is the capacitance in micro-farads (uF) and V is the Voltage the capacitor is charged to in Volts.
Here is a good video that shows you how to wind your coil:
How to Wind a Coil
-Bolt of an appropriate length and diameter
-Large diameter washers and nut to fit on the Bolt
-Electrical (usually black) tape or preferably super glue or epoxy
-Straw or paper to create a space between coil winding and the bolt
-Magnetic or Enamel wire
-I use Plexiglas washers created via a hole saw and drill press. This allows you to super glue each layer to the plastic washers that way the coil is more structurally sound when taken off the coil. If you choose to have plastic washer you can feed the starting wire through a grove or hole cut in back plastic washer, this aids greatly in winding.
Now, get your straw or piece of paper and cut it about 1-2 mm longer than the desired length of your coil. Put the end washer(s) on the bolt and place the straw or paper on the bolt as shown in the picture, if the straw doesn't fit on the bolt simply cut it length wise.fit the remaining washer and nut on the bolt as shown.
Feed the end of your magnetic wire though the center of your end washer and allow about 2-3 in of the wire to come out the other side. Wrap the wire that was put through the end bolt around the head of the bolt to secure it in place. Now start to wind the coil in a clockwise or counter-clockwise manner around the bolt. DO NOT switch from counter-clockwise to clockwise or vise versa, always wind in one direction around the bolt, otherwise your coil will not work. Continue to wind until you have reached the other end, secure the wire with your thumb and if you have tape tap the layer down tightly, if you are using super glue DO NOT glue the first layer, this will glue the wire to the straw or paper.
To make a second layer simply continue to wind, rotating in the same direction you started and making you way back to the other end of the coil on top of the first layer. Once you have reached the other side glue or tape the assembly and continue to wind in the same clockwise or counter-clockwise direction back and forth along the length of the coil. Wind the coil as perfectly as humanly possible and keep the wire as perpendicular to the bolt as possible.
Once you are done with your coil tape or glue the assembly as tight as possible and let it sit for few hours. Then, take the coil off the winder as carefully as possible and remove the inside of the straw or paper with pliers.
To Make the Guns grip open the plastic handle and hot glue in the roller switch so that the switch is triggered by, well, the trigger. Drill holes in the back and attach wires to the switch (1,3) and then put the wires through the holes. Close the Handle and if you can hear a click when you pull the trigger it should work.
A relay has two working elements in it, an electromagnet and a mobile contact.
First a little Vocabulary:
- NC-Normally Closed-When no current is applied to the electromagnet C and NC are connected
- NO-Normally Open-When current is applied to the electromagnet C and NO are connected
- C-Common- Connected to either NC or NO based on state of electromagnet
- SPST- Single Pole Single Throw- Either NC or NO is included in this relay, not both
This relay will have 4 connections, Although some appear to have more, If the location of the electromagnet is unknown apply a 9V-12V source to each connection combination possible until a click is heard, this is the electromagnetic and when the relay is hooked up as in the diagram in the subsequent step the gun will fire when a proper voltage is applied to these connections again.
- SPDT- Single Pole Double Throw- Both NC and NO are included in this relay(Shown in Picture below)
This relay will have 5 connections, Again If the location of the electromagnet is unknown apply a 9V-12V source to each connection combination possible until a click is heard, this is the electromagnet and when the relay is hooked up as in the diagram in the subsequent step the gun will fire when a proper voltage is applied to these connections once more.
For this Project either a SPST or SPDT Relay can be used, we only use the C and NO connections so a SPDT will have an unconnected Lead.
Opening the Relay will allow you to find these connections more quickly, but put the cover back on when your ready to install the relay.
Also Below is a picture of the semiautomatic configuration.
Step 3: Coils, Capacitors, and Results
All measurement are taken from velocity test with chronograph and are maximum achieved.
-UM:7 Layer, 33mm L, 6.5mm InDia 1320uF 330V E.37m/s 4g(11*330V 120uF)
-8 Layer, 30mm L, 8mm InDia 960uF 350V 24m/s 8g(8*330V 120uF) 3.9%
-12 Layer, 30mm L, 8mm InDia 600uF 350V 12m/s 8g(5*330V 120uF) 1.57%
-12 Layer, 30mm L, 8mm InDia 470uF 450V 27m/s 8g(1*400V 470uF) 6.1%
-16 Layer, 30mm L, 8mm InDia 470uF 450V 28m/s 8g(1*400V 470uF) ****Best results 6.6%
-UM:12 Layer, 30mm L, 8mm InDia 470uF 800V E.>50m/s 8g(4*400V 470uF)
-UM:12 Layer, 29mm L, 8mm InDia 940uF 400V 31m/s 8g(2*400V 470uf)
-UM:12 Layer, 12mm L, 8mm InDia 1200uF 350V 26m/s 8g(10*330V 120uf)
-8 Layer, 12mm L, 8mm InDia 880uF 450V 13m/s 9.0g(4*400V 220uF)
-Ferrite Surrounded-8 Layer, 12mm L, 8mm InDia 880uF 450V 14m/s 9.0g(4*400V 220uF)
-8 Layer, 30mm L, 8mm InDia 1100uF 450V 33.0m/s 9.0g(5*400V 220uF) SCR Switched 4.4%
E.=Estimated Velocity-The velocity here is estimated based on visual comparison to the other results, they are Not measured.
UM=Unmaximized- Coil not experimented with to achieve maximum results
If you do not have access to a chronograph the method HERE is relatively accurate.
If you use this method to get velocity results make sure your coil is perfectly horizontal and don't fire to the ground, fire at a piece of foam that is a meter or so away.
Also HERE is an optical velocity measurement set up.
Even at best the shown results are + or - 20% correct, this is because most electrolytic capacitors capacitance rating is within the + or - 20% region.
Step 4: Bring It All Together
Test the system, if it works use Plexiglas, wood, or even metal to make housing for your gun depending on the desired size/weight etc.
The Battery Banks Must not exceed +3V for relatively safe operation.
Step 5: Projectiles
The projectile material is a very important part of your coilgun system.
-Basically your projectile must be ferromagnetic, i.e contain mostly Iron.
-It must be magnetically soft, which means that if a magnetic field is applied to it the material will not stay magnetized.
-It must have the highest magnetic saturation point possible
The Best Materials I know of are listed below from best down:
Low Carbon Steel (Steel with a rating of 10XX where XX is the lowest number possible, such as 1006)
Stainless Steel - Most stainless steal is NOT ferromagnetic, it must contain at least 80% Iron to be considered ferromagnetic.
Round Low Carbon Steel 1006 from McMaster-Carr will be the best material I found for your projectiles for a reasonable cost and availability. It is the lowest carbon steel I could find for "low quantity" purchasing.
If you want efficiency in your coilgun but don't have the tools, time, or effort to make your own projectiles buy HERE, you can customize your rod cuts for a relatively low price and you don't have to do the tedious work, and the steel is low carbon, which means higher iron content and more efficiency. Also they sell acrylic for my casings, which is a plus.
Now this is the "Hardest" and most time consuming part. In order to make the projectiles, cut the heads off of the nails using a Dremel tool with a reinforced cutting disc (will wear quickly) or a large grinder with a cutting blade.
You can also use a hacksaw with a steel cutting blade, credit for this idea goes to member jondo huang, I never even thought of it. This is the preferred method as it is cheaper and the cut is much better.
Then cut the rest of the nail to the correct length ( They should be 3/4 to 5/4 the length of the coil). If you are looking for efficiency, i.e. velocity, simply grind the edges of the projectile to a rounded flat surface and not pointed.
Mine are sharp so they can do more damage. In order to do this I placed the projectiles in a drill press and used the grinder to grind the edges down, if you use the Dremel you can get a smoother finish and finer point. This can be a long process, but well worth it.
You can glue smaller diameter straws to the end of the rounds to stabilize them, usually the longer the round, the longer the stabilizer will have to be to ensure level flight.
Step 6: Coilgun Research and General Information
Experiment with a different amount of capacitors to maximize the Muzzle Energy.
-Potential Energy=(1/2)(capacitance in uF/1,000,000)(voltage in V)2
-Kinetic Energy= (1/2)(mass in g/1,000)(velocity in m/s)2
Equations for Capacitors in Parallel
-Capacitance(C) total=(C of 1st capacitor)+(C of 2nd Capacitor)+...
-Voltage(V)max= Lowest rated Voltage
Equations for Capacitors in Series
-1/(Capacitance(C) total)=1/(C of 1st capacitor)+1/(C of 2nd Capacitor)+...
-Voltage(V) max=(V of 1st capacitor)+(V of 2nd Capacitor)+...
I take no responsibility for your actions. If you shoot, shock, or otherwise injure yourself or others, Your
On Your Own.
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