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Registered Member #1889
Joined: Mon Dec 29 2008, 07:36AM
Location:
Posts: 55
The sensors are mounted in HDPE (High Density Polyethylene) lol. I'm might stick with the small gauge to get a higher turn density. It serves my purposes pretty well because my inductance need to remain very low so my coils have to be small. If I was to use the thicker gauge it would help keep resistance low but I would lose turn density (leading to a drop in field strength).
Guitardude, you wouldn't happen to have any digital oscilloscope graphs for the 16AWG? If they look promising I might try it out to see what kind of results I can get out of it. I also might try putting it through a spice model so I can observe the differences. The first coil will have a higher inductance, just so I don't waste an incredible amount of energy but like everyone is saying I'm not sure what the losses will be to resistance.
I calculated a 2000amp surge with the coil resistance for 20ms and I only lose roughly 28 joules of energy. But as the temperature of the copper rises so does the resistance. Just not sure what the effects will be.
@El_Roberto
I used nylon rod at first and it was terrible to work with. If you try drilling, cutting, or shaping it in any way it tends to want to melt. The HDPE I'm using was great to work with. Just run a few pieces off with a lathe, then get out your drill press and go at it. I did some design sketches in solidworks that represents a few ideas that I had for a more polished look. If your interested, PM me and I will upload them onto my server for download.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
2000A surge for 20ms? Do you have a O-scope available? If you do, you should consider designing a rogowski coil.
If you use a PC sound card for speed measurment's, you can hook up a optoisolator and a voltage devider that shows you pulse width and wave form, any ringback, and time. It is very usefull for data. You can use that information with speed data and coil length to calculate if you have any suck back.
Registered Member #968
Joined: Fri Aug 24 2007, 04:54PM
Location: Norman, Oklahoma
Posts: 104
blackgrunge wrote ...
Guitardude, you wouldn't happen to have any digital oscilloscope graphs for the 16AWG? If they look promising I might try it out to see what kind of results I can get out of it. I also might try putting it through a spice model so I can observe the differences. The first coil will have a higher inductance, just so I don't waste an incredible amount of energy but like everyone is saying I'm not sure what the losses will be to resistance.
I do have some older scope captures with 14awg, mostly of speed gates though .... what exactly where you wanting to see? I don't have coil voltage over time graph...
I just quickly put those coil values into barrys RLC sim, and got a peak of 500A, only dropping to 100A after 40ms.....did i do something wrong? because that sounds wayyyy too long to me. Even if you turn the coil off as soon as the projectile has passed, your only going to have used maybes 5% of the stored energy...
Registered Member #1889
Joined: Mon Dec 29 2008, 07:36AM
Location:
Posts: 55
@rp181 How would you go about using a sound card to measure speeds? I have an old PC sound card (really old) lying around that I could use.
I'm using 31200uF (31.2mF), 8 x 400v 3900uf capacitors. I'd have to ask for access to my local universities oscilloscope if I was to do that and I'm trying to save up my brownie points for when I really need them.
@guitardude012 Oh, I was wondering if you had any current vs. time graphs with a quenched coil. I'd really like to see a oscope graph with the coil shut off prematurely while a quenching diode was used. Not sure if you've done anything like that but I thought I'd ask.
@big5824 That's exactly what I want. I don't want even close to all the energy used in the first stage or it would defeat the purpose of my approach. You can read more about what I'm trying to do in some of my larger posts in this thread (coil shut off, quenching, triggering, etc.). If I use too much energy in my first coil I'd never make it to the rest of the stages. If anything I might consider increasing the inductance a bit just to save as much energy as possible. The only thing I'm really concerned with is ramp up time. I'm not concern with fall time because the circuit is quenched and the coils are being shut off.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
Im bored right now, so ile put of a page on my site explaining it. You don't need a separate sound card, the one in your computer works. How are you measuring speed now? As for capacitors, i was thinking 6 because thats how many im using =p
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
Why does your school have a chronograph? Anyway, i got the page up under data acquisition-optical speed trap. Read near the end and you will find a section on measuring the current rise vs. time, peak current, etc with a PC sound card. Site in sig.
ah yes i read further back again and i understand what your doing now, and i have to say it is a very interesting idea, im guessing the coil inductances will drasticaly reduce down the gun as you need shorter pulses and have a lower voltage available?
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6 Month Gauss Cannon Project
