Coil Gun test firing.

 

Maybe I didn't shoot very far, nor punch any holes in tin cans.. but still pretty good for first attempt I think!

Using the scavenged Back EMF really added some kick to the firing! It may be a strange use of a relay, but its a new trick in my toolbox. :) But first lets get some Hero shots of the coilgun in all its glory.

Still brings a smile to my face. I'm glad the failed symet spinner capacitors found a new home. The rings were kept from the old design, and added a nice "raygun" look to the little cannon. I suspended the coilgun in the middle on the rigid solid core wires, hoping for a recoil effect as it shoots (not enough power yet for that). The barrel is a brass tube, so it wont mess up with the magnetics of it all, and the outer ring is + and the inner ring - of the capacitor bank.

The Capacitors were angled forward a bit, and the rear ring was bent back some, to give it a bit more of a tripod look, as well as some more interesting angles to look at. And of course it HAD to appeal to my sense of aesthetics... like a Corvette, if the coilgun LOOKS like its shooting even when it isn't, well then it MUST be cool!

 

Here is the new fangled power booster, fresh from the Back EMF experiments. Reading back, you could see how it is truly a booster, in that I put 7v in, and the back EMF it generates trickle charges up the capacitor bank... to 23volts!  The white sleeved leads are the EMF, the unmarked are the power. The only real drawback is the whine the clacking contactors do on it as it cycles.. at about a 400 hz whine. (one I recognize from my Air Force days)

After trying to get a 555 timer to monopulse to make a quick fire of the capacitors through the coil, to looking into using a camera flash trigger to do the job, I instead went old school: relay logic (!!), as something I could wrap my head around, and had past experience with, as well as something I could build right then with parts at hand.

So here it is. 2 double contactor relays, and 2 pushbuttons. The function is straightforward, if a little interconnected: the left relay is the arming relay, the right one is the fire/disarm relay. The top left contacts act as a holding circuit, that keep that relay on once I press the button. The bottom left contact is the Enable, sending power to be available at relay #2. Relay2 wont energize until I complete the ground with the other pushbutton, the fire button. When the relay energizes, two things happen: the bottom right contact switches the contacts, moving the connection of the capacitors from the power source to the coil for as long as the relay is on. That wont be very long, however, as the top right contact breaks the ground to Relay #1... which you may remember, was supplying power to relay2 so long as IT was on. So, what happens is the firing relay turns on-OFF really fast, but long enough for the bullet to be fired.

 

Here's the wiring schematic, for anyone whose interested. This is a simple way to have a pulse of capacitor dump that is only a fraction of a fraction of a second. Maybe 100ms or so. A quick on-OFF is important to shoot something with a coil, as if the power stays flowing too long, the coil will just be a magnet, sucking the bullet to the center of the coil, and keeping it there. The Capacitor bank I had held enough power that the discharge time would have been too long for them to just dump their charge, so I had to engineer a rapid switching pulse... thingy.

I could adjust the "on time" by simply adding a capacitor across relay2's coil taps.. when relay1 kills its power, the capacitor will leave it on a little bit longer... but just like this seemed to work the best.