23 stage no-capacitor full auto coilgun Answered
*********I have updated my design since posting this topic. The video is the more current design than what is written below.**********
I came to the conclusion that using capacitors to provide the power for a coil gun is a stupid idea. A bold statement I know. The reason is that they are big and heavy, take time to charge, and need charging circuits. Also, the sharp rise in current that comes from capacitors is bad unless you are making an induction style coilgun, because the induced currents will hurt efficiency.
If coil guns are ever going to be a practical hand held weapon it will need to be lighter, simpler / less delicate, and more powerful than what you will find on the internet if you look up coil guns. A rate of fire that is competitive with conventional guns will also be needed if a coil gun will be used for anything other than target shooting or maybe hobby hunting. So I designed a coilgun to meet these requirements. Visit my website for a full explanation of the design: http://www.ourbadscience.com/#!em-guns/cwjy
I realized that a coilgun would not be a practical infantry weapon until batteries are more advanced anyway, so that just adds to the list of why capacitors are out. It will be powered directly off of the batteries, and have many coil stages. This allows a very high rate of fire. To get that rate of fire with capacitors you would need several capacitor banks charging at offset times, so after each bank fires another is just finished charging. That would be terribly bulky.
The lower voltage from the batteries will give comparatively slow current rise in the coils which normally would make the coil timing weird. I plan to use an unconventional coil timing though. All the coils will be activated at once, and the coils behind the projectile will be shut off as it passes them. This will have several advantages:
-The coils will only be powering up for a split second at the beginning. Most coils will already be at full power when the projectile gets to them (that is not the case in most coil guns).
-Induced current will not be any issue.
-Since the coils will all act as one coil, the projectile will be drawn toward the center of all the coils that are on. Timing of the shut off of the coils will not need to be perfect.
This will be a pre-tuned passively timed system. I want to use a small adjustable electronic timer for the switch-off timing. This will require some work in the initial adjustment of the timing, but even actively switched coil guns (with optical sensors or something) require that. the advantage of a passive system over an active system is cost and simplicity, and you can pack the coils tighter on the barrel if you are not putting a sensor between each stage. That matters with 23 stages!
As I said check out my website to see more details and pictures for this and other projects: http://www.ourbadscience.com/#!em-guns/cwjy