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Specifics of building a multi-stage coilgun? Answered

So I recently decided that I wanted to build a coilgun. I already knew how they function, and after some light research, I've got the main design already laid out.

What I'm looking for now is some more detailed input on the exact power requirements, circuitry, etc.

Specifically: Firing a standard .177 steel BB, I want to use many small coils in series as opposed to one/few large ones. From my understanding, this will provide better end speed while keeping each coil's power draw relatively lower, and thus safer. (Am I right about this?) How many coils should I use, what would be overkill, etc?

Each coil will be triggered sequentially by a IR LED/photocell trigger system rigged through tiny holes drilled across the barrel. Will a simple on/off circuit suffice, or will the projectile pass by too quickly for the full charge to release? If so, I assume I need a system to trigger a full discharge when tripped. Correct or not, and if so, how?

I'm also considering fitting an extra gate at the end to trigger a circuit to bleed any remaining charge. Ideas on this?

What size of capacitors should I use, and how would I charge them? The only thing Google can seem to turn up is camera flash circuits, but I'd much rather have one tailor-built to the system's exact levels. I'm going to use a press/hold switch to charge them, and would like an automatic shutoff with an LED that comes on when they are charged, but turns off when I release the button. Kind of like a camera flash, actually.

I'd like to fit it with a re-chargeable battery. What sort of power is required here? How many firings would I likely get per charge, etc?

What sort of muzzle velocity can I expect? I don't want to kill bears with it, but soda cans would be nice. I don't want to waste my time fabricating it only to be able to stop it with my eyeball.

Lastly, are there any other points of concern or things I should know?

Thanks for any input, and if everything ends up coming together nicely, I'll be sure to properly document the process for everyone's enjoyment. :)


No file found... Seems like i made only the printout back then 5 or 6 years ago...
Maybe i recreate the schematics sometime...

Oh: And about the charging-circuit:
I simulated once one which is simply a coil (Large) which i energyce and then cutt off. By the selfinducing voltage the energy remaining in the coil gets (partly) pushed trough a diode into the cap.
iI simply checked if the current in teh coil fell to a certain level and repeated the process.
A simple opAmp-circuit made sure the cap got a tickle-charge for maintaining its target-voltage...
If you want, i can see if i find it again...

See V-Switch: http://www.coilgun.info/mark4/diode.htm and the link on the page...

By my tests, the only "switch" capable of cutting the HUGE current fast enough is a small subcircuit called a V-Switch. It is in fact 2 Tyristors and a second small, but high-voltage cap.
I havent seen any modest cheap switches that can handle that big current and arking and act (shut off) this fast...

And dont think you are done by just switching the coils ON in sequence... You need to cut the coild OFF at the the exact moment the projectile is in the center of the coil or the magnetic fieldf will decelerate or even stop the projectile in its center --> The projectile will go to the center of the coil and stopps there.

The bleeding at the end of it... Well... Depends on what you want to do.
If you want a multi-projectile-mag, you dfont want to do that and just fill up the partially drained caps.
Maybe you simply add a little momentary switch which fires a thyristor to a resistor to let the caps bleed out? Of course the Resistor has to withstand the voltage and wattage (Energy) of the caps maximum load.

Also consider making the spaces from coil to coil increasing with distance... The projectil will become faster and faster and if you dont increase the spacing, your timings will becomme smaller and smaller and more difficult to control...