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Work in progress ~350J 2stage coilgun

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Bonehead

Mon Apr 06 2009, 12:04AM

Registered Member #2046 Joined: Sun Mar 22 2009, 01:12PM
Location: Stockholm, Sweden
Posts: 23

Hmm, where to start... Well, this is the 2 stage coilgun rifle I'm working on.. I got 8x 560ÂµF@400V capacitors available for the build, which makes around 350joules I think?
Bolt-action, magasine-fed. Everything is metal, steel, plastics and so on. Projectile is cut from a bolt and weighs around 70grams.

The electronics are pretty weak so far since I'm not very good at it. The cap-charger consists of a NE555IC which oscillates a BD243C power transistor, which goes through a transformer which gets rectified into the main bank...
Sadly I didn't know that the 555 could only supply around 200mA when I ordered the self-designed PCB so I can't use the BD243C to it's full potential since the HFE isn't big enough.
Eventually I'm gonna do a darlington to pull more amps through the transformer and hopefully decrease the chargetime.

On the issue of firing/timing the stages I was thinking of having 2 V-switches, one for each stage but then I got lazy and decided to just seperate the capbank when firing and let them run dry.. I'm still working on how to detect the bullet to trigger the second coil.

I'm a poor writer so I'll let the pics tell the rest.

I got some older pics of this thing in development and other random crap @ my blog.. Check my "homepage" if that seems interesting. I will post further updates on this project here and on the blog so you won't miss anything.

hotcrazyfruit

Mon Apr 06 2009, 03:53AM

banned on 5/26/2009
Registered Member #1877 Joined: Mon Dec 22 2008, 02:03AM
Location:
Posts: 147

wow looks really cool i recently made a 500 j coil gun, and used a carbon arrow as a barrel. it works amazingly. single stage i used a triac bank (its all i ahd laying around) and threw two 2 inch by 5.25 inch caps in a piece of pvc pipe, connected em with some 12 gauge wire and voila i had an awesome sniper rifle. yours looks good too. any other specs?

Bonehead

Mon Apr 06 2009, 11:58AM

Registered Member #2046 Joined: Sun Mar 22 2009, 01:12PM
Location: Stockholm, Sweden
Posts: 23

Name any specs you're interested in and I'll type up what I have or got planned.

Things I think I missed: 1.2mm magnet wire for both spools, although I think they might have too high resistance at the moment so I plan to remove a fair bit of turns later. I will try out optimal turns for this size of coil using a single stage setup.

In the future I think I will make a rifle with a smaller caliber since when the bullet is this big you need TONS of power to get any kind of decent speed out of it.. My single stage experiments has so far only yielded about 4-6m/s.. But first I need to finish this before trying other calibers.

Oh yeah, the stock was made from a used 2"x4", hence the random holes and bad finish.. Handle was also made from a 2"x4" but a bit better quality in that one.

guitarlord66

Mon Apr 06 2009, 12:07PM

Registered Member #1805 Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67

How did you make the clip? I'm having heaps of trouble making one for my coilgun...
I'm using a solenoid to inject the projectiles into the coil though instead of bolt action.

Bonehead

Mon Apr 06 2009, 06:07PM

Registered Member #2046 Joined: Sun Mar 22 2009, 01:12PM
Location: Stockholm, Sweden
Posts: 23

The clip was actually the biggest bother to make in this project.. I bent two U-shaped pieces from sheet metal, had my brother weld them together. Then I made several different designs of the piece that slides within and how to spring-load it..

An early design was like this:

Had a bolt inside it with a spring around it, allowed for easy adjustment but since the bolt followed the tray you had a big bolt sticking out the bottom when a the clip was loaded...

Current design is something like this:

This way you still have a stable spring but don't need to have any guiding bolt for it and you also save some weight. Downsides are that you have to bend spring metal with pliers to get the spring you want, takes a long time and is a big nuisance..

guitarlord66

Tue Apr 07 2009, 11:32AM

Registered Member #1805 Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67

Awesome thanks,

I am going to try making mine out of plastic but thanks for the design tips!

hotcrazyfruit

Wed Apr 08 2009, 01:56AM

banned on 5/26/2009
Registered Member #1877 Joined: Mon Dec 22 2008, 02:03AM
Location:
Posts: 147

Bonehead wrote ...

Current design is something like this:

This way you still have a stable spring but don't need to have any guiding bolt for it and you also save some weight. Downsides are that you have to bend spring metal with pliers to get the spring you want, takes a long time and is a big nuisance..

thats how modern clips are made. with a spring that spreads from side to side in the clip, it allows for alot more ammunition to be help as well, as the spring compresses more than the one you had before, another advantage is that it provides constant pressure even when the last bullet is in the receiver. iv got this transformer that can charge a 262.5 joules cap in about .2 seconds, so im thinking of parralelling that transformer with another, and then have a fully auto gun. but it seems your beating me to it.

Bonehead

Fri May 08 2009, 12:37AM

Registered Member #2046 Joined: Sun Mar 22 2009, 01:12PM
Location: Stockholm, Sweden
Posts: 23

Managed to grind out a new bullet:

Did a testrig so I could test out different things a bit easier(starting position, capacitance for first stage etc)

It's quick and dirty, there's more info on it on my blog ...

After I finished the test rig Idid some more research and tested Barry's (quite excellent) RLC simulator to get a hunch of how the current wave looks like, it's pretty horrible for my testrig.. As noticeable, there's a lot of bouncing and the coils on the 2stage rifle are similar.. It still has pretty high currents up to 10ms which is far from ideal.
Testrig:

First coil in 2stage:

I also tried to construct an inverter logic, which I successfully did but realized that I didn't have anymore thyristors anyway so it was a waste of time...

I also did a weak attempt at having the second stage "spark triggered" so I wouldn't need all the logic... All that did was give me a horrible pain in my ears(forgot headphones eh ..), gave up on this with the reason that even if I do get it to work it'll be too wasteful of energy and MUCH too loud, logic and photogates is the way to go!

Bonehead

Thu Jun 18 2009, 04:49PM

Registered Member #2046 Joined: Sun Mar 22 2009, 01:12PM
Location: Stockholm, Sweden
Posts: 23

FINALLY managed to purchase some bits for this project. Some logics, voltage regulators and SCR's.
Unfortunately the some of the logic chips turned out ... Quite a bit smaller than I hoped for.

I'm not even sure if I can solder those ..

But hey, at least I got my 20 x 30tps12(300A Itsm 1200V) so I can start testing the second stage..

Bonehead

Sun Jun 28 2009, 03:12PM

Registered Member #2046 Joined: Sun Mar 22 2009, 01:12PM
Location: Stockholm, Sweden
Posts: 23

Started working on the stationary charger for the coil-rifle, it will have a mobile charger aswell later on. 230VAC in, 325VDC out.

12A rectifier on custom PCB, milled by hand with a drill press :X ... Charge current is adjustable by changing bulb, current 75W lamp gives out 6.2A if my math is correct.

Added in a little 12V transformer aswell so I can put in a fan later for eventual cooling.

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