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Hello everybody, I'm planning to build a coilgun. I've already chose some of the basic features: -Multistage (at least 3 stages); -Charging method ( solid state boost converter); -Switching method ( MOSFETs ); -Chassis (i'm going for a Barret M82-like appearance, just because it looks cool ;) ); -Security Measures (Diodes against voltage spikes, some safety switches here and there to avoid accidental discharges and/or other dangers, a bleeder resistor to discharge the capacitors when turned off);
Anyway, I'm still unsure about the propulsion system: obviously, the MAIN propulsion force comes from the coils, but I was thinking about using an airgun-like piston to push the projectile into the barrel, instead or relying on the first stage of coils. This way I could use all the stages for acceleration (or so I think, correct me if I'm wrong), also the projectile should have a greater exit velocity from the barrel (excluding magnetic saturation problems) and consequentially a greater kinetic energy.
Registered Member #2648
Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291
Hello and welcome.
You might want to make a post here: to get this thread moved to: where it would be more relavent.
1)If you're doing multi stage make sure you got enough capacitance and good pulse control. 2)A boost converter sounds great. Make sure you got one with the right input/output voltages. 3)MOSFETs that can handle the voltages and currents in a coilgun can get expensive, You might want to consider an IGBT instead. 4)Good luck managing to fit everything into something that size and shape =/ 5) Diodes are good against the inductive kick back but beware that it increases the turn off time of your pulse. Switches to disconnect your charging circuit is a good idea. Bleeders are a good idea too.
Injection is not a new idea and certainly works well. Pneumatic injection is commonly used in railguns but in coilguns a push solenoid is more pracitcal. The solenoid pushes the projectile out of the clip and into the coils and just requires another capacitor. Rather than pneumatic inject which requires an enclosed barrel, tubes, air tank and pump. If you look around the coilguns sites, many use solenoid injection.
About the IGBT, which one could you reccomend me to handle voltages about 400-500V? And if possible, where can i possibly salvage some high power transistors?
Registered Member #2648
Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291
Suitable IGBTs can be found on ebay for around $30 with post postage. You should note: "The highest voltage the IGBT has to block should be no more than 80% of the Vces rating." source: you should also note the currents involved in coilguns which can easily go 500+ amps. So make sure that your IGBT can handle the surge current. The IGBTs in the 1200v 300-400A zone mostly appear to handle double the average current for 1ms. Look at the RLC sim on Barry's site for a rough idea of your pulse characteristics and over-rate.
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
I bet you could fit it all into a Barret-sized frame. My 1.2kJ single stage bolt action coilgun is shorter than a retracted-stock m4 and maybe twice as wide.
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Coilgun questions: airgun-like initial propulsion or not?
