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Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
hi i've started construction on a six stage cg that is optically triggered with 560 uf 330v capacitor bank per stage. my question is that with the first stage i have a ten layer one inch long coil of 18 gauge wire and i get the most velocity with the projectile starting inside the coil a little ways. Does this mean that my discharge time is too short? Before i hade the coil with only 8 layers and the projectile had the highest velocity with the starting point at the very start of the coil. Should i add more layers to increase the discharge time? Should i use a smaller guage wire to add more turns per layer? By the way so far i'm getting ~5% efficiency and 24 m/s with two stages. any help would be great, thanks
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
by grip i mean more magnetic feilds interact with it, giving it faster acceleration, starting outside the coil will give a longer acceleration period, but the rate will be slower.
This is all theoretical for me, so if someone thinks otherwise, say so.
Registered Member #1464
Joined: Sat May 03 2008, 10:56AM
Location:
Posts: 9
What kind of switch you use? And what is the ohmic resistance of coil? (1 inch long, 10 layers, 18AWG, I gues around 0.25 ohm) If you use MOSFET or IGBT (allows turning off the current) and if your coil have smaller resistance than 1 ohm, I think you should have increase number of turns, or use thiner wire, or increase capacity (2000uF/stage will be enough). Definitely one of these solutions helps you increase length of current impulse. And working area of one stage too.
BTW how long is your projectile? In my design, projectile length is equal to coil length. Starting position - front edge of projectile on rear edge of coil. In this position achieve best efficiency.
5% efficiency and 24m/s are very good, with all 6 stages will be powerfull enough.
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
i'm using an scr and my resistance is around .2 ohms... but i wouldn't really trust the resistance number too much becaue of the tolerance of my meter. My projectile is 1" long and 1/4" in diameter. I made another coil with 22 awg wire and about .8 ohm with same dimension and i still had the best velocity with the starting point in the coil a little ways.
Registered Member #1464
Joined: Sat May 03 2008, 10:56AM
Location:
Posts: 9
If you using SCR, I can't help you. I focused only on design where I can switch on and off the current through coil. Last 3 months on IGBT halfbridge design. With SCR you must experiment with coil resistance, capacitor bank and starting position in order to decay coil current if projectile is in middle of coil. That's all.
In my opinion tunnig 6 stage coilgun (SCR triggered) will be a hard work with rewinding coils.
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question on tuning a 6 stage gc
Half the fun of coilgunnery is the design and building of it... and besides i enjoy the challange.