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banned on 5/26/2009 Registered Member #1877
Joined: Mon Dec 22 2008, 02:03AM
Location:
Posts: 147
El_Roberto wrote ...
Yea before I left for uni I was building a 2kj 6 stage coilgun and while I never made more than one stage (I couldn't afford it after paying uni fees) it could still shoot through about three cans (~300j source, 2/3 charged). So I think ~250j per stage works great, but your scr's wont be powerfull enough, my last stage (had I completed it) would have a peak current of around 4500amps. Of course you could use a large bore size to reduce projectile speed and then the longer pulse would have lower current.
iv got a really hard time beleiveing that it would give 4500 amps, how did you run calculations? because even in one millisecond (a VERY fast discharge time), a 262.5 joule cap would only put out 550~ amps. and not to mention the faster the discharge time, the MORE the scr can handle in the shorter time period. how did you calculate your amps? i always take the number of joules (and since 1 kilowatt hour is 3 600 000 joules) by voltage then by discharge time, which can easily be assumed between 1 and 10 milliseconds, or you can calculate it, but it takes more math.
Registered Member #1774
Joined: Wed Oct 22 2008, 02:51AM
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Posts: 135
I used barry's calculator on his site, and I cant remember how long the pulse time was but I THINK it may have been 1.2ms (And this was with my 350j capacitors not with them half charged)
banned on 5/26/2009 Registered Member #1877
Joined: Mon Dec 22 2008, 02:03AM
Location:
Posts: 147
El_Roberto wrote ...
I used barry's calculator on his site, and I cant remember how long the pulse time was but I THINK it may have been 1.2ms (And this was with my 350j capacitors not with them half charged)
o ok, i didnt know barry had a calculator, i might have to use it then xD
Just a regular RLC discharge graph, that doesn't really tell you anything more than the standard equations for a damped oscillator. But it's really, really easy to use.
Cheers, Barry Why don't you ever see the headline "Psychic wins lottery".
Registered Member #1694
Joined: Sat Sept 13 2008, 09:13AM
Location: Australia
Posts: 108
Basically its a wheatstone bridge with a comparator . The 2k resistor might need changing depending on how much the resistance of the photo diode varies with an IR LED shining on it.
Registered Member #1819
Joined: Thu Nov 20 2008, 04:05PM
Location:
Posts: 137
Barry wrote ...
Spacing the coils in various ways won't have any effect on each stage's timing. Instead, I recommend building subsequent coils with progressively lower inductance to achieve a shorter LC time constant, which has the desired effect of shorter pulses.
You still need to compensate for flux density in the projectile. The flux in the projectile has to drop far enough so that the flux from the next coil will not cause it to saturate. Unfortunately, optimizing this aspect of the coilgun usually requires trial and error, unless you have a full list of material specifications for your projectile. With even spacing between the coils, the projectile can saturate, depending on your input voltage and specific coil design. It might be possible to simulate all of this in FEMM.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
killah573 wrote ...
You still need to compensate for flux density in the projectile. The flux in the projectile has to drop far enough so that the flux from the next coil will not cause it to saturate. Unfortunately, optimizing this aspect of the coilgun usually requires trial and error, unless you have a full list of material specifications for your projectile. With even spacing between the coils, the projectile can saturate, depending on your input voltage and specific coil design. It might be possible to simulate all of this in FEMM.
You have something in mind here that seems important but I don't quite follow what principles you're looking at. Please explain in detail. Sorry if I'm having a bad brain day.
What exactly needs to be compensated? Why? What does 'even spacing' have to do with it? And precisely what is bad about saturation?
banned on 5/26/2009 Registered Member #1877
Joined: Mon Dec 22 2008, 02:03AM
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Posts: 147
killah573 wrote ...
Barry wrote ...
Spacing the coils in various ways won't have any effect on each stage's timing. Instead, I recommend building subsequent coils with progressively lower inductance to achieve a shorter LC time constant, which has the desired effect of shorter pulses.
You still need to compensate for flux density in the projectile. The flux in the projectile has to drop far enough so that the flux from the next coil will not cause it to saturate. Unfortunately, optimizing this aspect of the coilgun usually requires trial and error, unless you have a full list of material specifications for your projectile. With even spacing between the coils, the projectile can saturate, depending on your input voltage and specific coil design. It might be possible to simulate all of this in FEMM.
saturation is a GOOD thing. it means the projectile is recieveig electormagnetism. th thing with saturation, is there is a limit to it. which is why people build multi stage guns, to allow the projectile to de-saturate, before you re-satureate it.
Registered Member #1694
Joined: Sat Sept 13 2008, 09:13AM
Location: Australia
Posts: 108
hotcrazyfruit wrote ...
killah573 wrote ...
Barry wrote ...
Spacing the coils in various ways won't have any effect on each stage's timing. Instead, I recommend building subsequent coils with progressively lower inductance to achieve a shorter LC time constant, which has the desired effect of shorter pulses.
You still need to compensate for flux density in the projectile. The flux in the projectile has to drop far enough so that the flux from the next coil will not cause it to saturate. Unfortunately, optimizing this aspect of the coilgun usually requires trial and error, unless you have a full list of material specifications for your projectile. With even spacing between the coils, the projectile can saturate, depending on your input voltage and specific coil design. It might be possible to simulate all of this in FEMM.
saturation is a GOOD thing. it means the projectile is recieveig electormagnetism. th thing with saturation, is there is a limit to it. which is why people build multi stage guns, to allow the projectile to de-saturate, before you re-satureate it.
ummmm no, saturation is generally a bad thing. The less energy absorbed by the projectile, the more efficient your gun will be. Have a look at a hysteresis chart for soft iron. You'll see the gradient is steepest as low levels of applied force. The idea of building a multistage coilgun is to apply small amounts of energy, many times over. The overall effect is much higher velocities than an equivalent single stage gun (which would waste lots of energy due to hysteresis losses).
banned on 5/26/2009 Registered Member #1877
Joined: Mon Dec 22 2008, 02:03AM
Location:
Posts: 147
Camel wrote ...
hotcrazyfruit wrote ...
killah573 wrote ...
Barry wrote ...
Spacing the coils in various ways won't have any effect on each stage's timing. Instead, I recommend building subsequent coils with progressively lower inductance to achieve a shorter LC time constant, which has the desired effect of shorter pulses.
You still need to compensate for flux density in the projectile. The flux in the projectile has to drop far enough so that the flux from the next coil will not cause it to saturate. Unfortunately, optimizing this aspect of the coilgun usually requires trial and error, unless you have a full list of material specifications for your projectile. With even spacing between the coils, the projectile can saturate, depending on your input voltage and specific coil design. It might be possible to simulate all of this in FEMM.
saturation is a GOOD thing. it means the projectile is recieveig electormagnetism. th thing with saturation, is there is a limit to it. which is why people build multi stage guns, to allow the projectile to de-saturate, before you re-satureate it.
ummmm no, saturation is generally a bad thing. The less energy absorbed by the projectile, the more efficient your gun will be. Have a look at a hysteresis chart for soft iron. You'll see the gradient is steepest as low levels of applied force. The idea of building a multistage coilgun is to apply small amounts of energy, many times over. The overall effect is much higher velocities than an equivalent single stage gun (which would waste lots of energy due to hysteresis losses).
ahh, i geuss i learn somethign new every day. lol. thanks.
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Multi-Stage coilgun
