Practical Coilgun Design 

Inductors 
Coilgun InductanceIs the inductance of the coil important? To try various values, see the interactive RLC simulation. Coilgun InductanceFor the best coilgun design, strive for the largest change in inductance between "no projectile in coil" compared to "projectile in the middle of the coil". That is, the more the projectile engages the field lines, the more it will affect the inductance. This is such an important aspect of rotary motor design, they gave it a name: saliency ratio. It is the ratio of maximum to minimum inductance. If you believe as I do that choosing projectiles and coil geometry is really an exercise in maximizing the change in inductance, then it leads to these conclusions:
Now... Is a large inductance bad? Is it bad to have a large number of turns or a great deal of external iron? It depends on whether the switching speed is important or not. I know it is true that: higher inductance > more turns > more wire > higher resistance But one type of coilgun is driving the coils with a square wave from a d.c. power supply. Once you turn on the juice, it will soon reach steadystate and then inductance doesn't matter. The property of inductance only helps to quantify what happens with varying current, such as ac signals used radios and tuned circuits. I believe inductance in a coil gun only tells you something about how long it takes to establish the magnetic field around the coil. It should be so short as to be negligible for all our calculations. 



Last Update 20080609
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