Finally, some help!

Erin's boyfriend, Matt Guthrie, looked over and ran some simulations on my schematic. All looks good, except using the light bulbs as a load to safe discharge the capacitor bank. I need to find some other high current, high resistance load to use.

Thanks, Matt!

A test, and a problem

I was concerned about how to wire the Variac. The instructions printed on the component said the primary conductors were connectors 1 and 2, and the secondary 1 and 3. Having the primary and secondary share a connection makes no sense to me. So, I tested it using a 18 VAC source and my voltmeter. Sure enough, it works.

The problem, shown in the picture is that the clear top of the case I am mounting the variac into doesn't give clearance for the arm to turn underneath. I'm supergluing oversized nuts into the case, then I'll superglue the correct sized nuts onto them to raise the height.

New Schematic

Stolen from XKCD.COM

A little work

I mounted my variable transformer om a plexiglas lid for a plastic box. I also finished essentially a GFCI protected, and switched, power outlet.

Not much, but something.

I hate Solder Bridges

Well, I took a day off to work on the gun. I soldered the transmitter and almost all of the receiver. Pics above of my work. Took a lot longer than I thought, particularly when I spent a minute clearing solder bridges for every minute of soldering!

I discovered that the transmitter board and battery won't fit in the project box I bought. Shopping opportunity!

I quit, and when to Ax-Man. I found enclosures to hold the caps and circuit boards, but not the transmitter.

Over the weekend, at the KBC (Keweenaw Brewing Company http://www.keweenawbrewing.com/ ) I was fortunate enough the engage 3 Michigan Tech Physics majors in a discussion of coil guns and Gauss guns. I now know what I am building is NOT a Gauss Gun, as it does not use permanent and electro- magnets.

A wonderful, wasted day!

KISS

I'm going to simplify the schematic. I'm changing the voltage for the "Top" Positive voltage line to 12 VDC, and eliminate a transformer and a bridge rectifier. I also wired the safe discharge load (two lightbulbs) in parallel. Someone tell me if this makes sense, or not! See the new schematic and BOM above.

Two suggestions

I have accepted two suggestions. First, Ryan T says I should include key locked safety switches. In fact, he suggested I should set it up that two keys would have to be turned at the same time. I'm not going that far.

The second, from Travis M., suggests a wireless remote firing mechanism, so I can be a safe distance away from the gun during firing. The images above reflect these changes.

I'd still like someone (like Matt G.) to review and comment on my schematic design!

Control Panel Layout

I decided on how I want the controls laid out on the control panel. See the picture below. I bought a variac on e-bay, so I've updated the BOM, also below.

I'm going to start thinking about my coil winding jig.

I've got an outline of the coil I'll wind. 10 ga magnet wire (the biggest I can get at Ax-Man), 3.5" long, (from the rule of thumb, coils should be 1 1/3 to 1 1/2 the length of the projectile), and the outer diameter not to exceed 1 1/2" diameter. However many layers I get in that volume is what I'll wind. to guide the magnetic flux, I'll use 3 1/8" steel washers at both ends of the coil, and if I can find an iron or steel pipe with a 1 1/2" inside diameter, I'll put the coil assembly inside it.

Updated Schematic, BOM, and some shopping.

I added a "charging resistor", corrected the capacitance for the caps used to control the pulse width range, added a master safety switch, and made a few general changes, based on my latest shopping trip to Ax-Man surplus. See the updates below. I bought a big heat sink, with a huge SCR and blocking diode installed. I thought it was a good $19 spent. When I got home, I couldn't find a reference sheet or specs for either. I guess I'll just try them.

The main capacitors are smaller than I thought they would be. Anyway, here are some component pics as well.

Schematic, proposed circuit

Here is my first draft of the circuit for the single stage coil gun. PLEASE let me know where I have erred.

Scope change, and other.

I've decided to focus on using finishing nails as the projectiles I will work with. Cheap, easy, aerodynamic, and pointy.

I've given up on extracting the wires from the AC motor I got. Each wire is passed through a tube with about 20 other windings, and I don't know how I would pull the wire out without breaking it.

Soon, I will post my first draft of the firing circuit for you, my readers, to comment on. Perhaps, even yet today.

But first, off to a wake.

Not much better, time to move on!

Well, on my bench configuration, I added a switch to I could disconnect the cap from the power supply after charging. Results were similarly feckless.

I also was given a 3/4 HP electric motor for recovery of the winding wire. I've got the armature out, and I think I'll see if there are any web links with ideas how to easily unwind a motor.

I realize I want to play around with different coil types and I want to control the pulse width when discharging the cap bank. I'm going to begin schematic design of a timing circuit.

A toy system, and first lesson

I put together a test fixture to play with. I'll post pics and a schematic in a little bit. As I pressed the fire button, I was entirely underwhelmed with the performance. The steel rod, at best, fell out about 3" from the coil. Adding a SCR and a trigger circuit might make a difference, as well as disconnecting the power supply.

I'll test dis-connecting the power supply after charging.

Also, my volt meter, during charging, slowly increased to about 7-8 volts, and stopped there. I expected it to continue increasing to about 12 volts.

Here is the parts list:

Note 1 is a 12 VDC benchtop power supply.
M1 is my trusty voltmeter.
C1 is a 15,000 MFD, 15VAC Capacitor ($3 at Ax-Man!)
The L1 coil is a random coil, also from Ax-Man. About 1" dia, 3" long, I.D of ~3/8"

Master Plan

Here's what I'm thinking about as an approach to learning:

1) Build a single stage, low voltage gun, largely patterned after Barry's Mark II coil gun. You have to spend time in his site, it's amazing!

2) Increase the size of the capacitor bank as far as practical at 19 - 30 volts.

3) Increase the charging voltage to 220 volts.

4) Design and build a 4 stage coil gun.

Welcome

I have taught classes inside my company on social media, but have never had anything I wanted to post before.

I'm going to try to design and build (or, adapt other's designs and cobble together) a few coil guns.

Helpful suggestions are always welcome.