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[ESSS]

I don't really know where to post this, but its physics,

 

I have a problem, recently I have been taking part in a scientific project, the project consists in the construction of a one stage coil gun, the idea and principle are simple, we have used capacitors to store the energy and then release it all in one go in order for the concept to work.

 

So we have souldered 20 capacitors in parallel onto two long copper wires, we then charge the capacitors (2200 uf 50v electrolytic) and release the charged energy into a coil, the magnetic feild created for an instant pulls the projectile through the coil and launches it, up to here no actual problem.....

 

now once done this we started experimenting with two different projectiles, one hollow and one full....as one might expect the full projectile resulted more efficient...... what happened then was that we tried adding more capacitors onto the system, now at that point everything goes weird, the full projectile was projected less further than with 20 capacitors (How does this make any sense?) it is possible that the discharge time for the capacitors became bigger and kept the magnetic feild on after the projectile whent through the coil thus slowing it down........

 

This seen we decided to try with 10 capacitors, so once again we souldered these capacitors to copper wires (still the same capacitors) and this time the results were excedingly confusing!!!! The hollow projectile found itself going further (10 cm more) than when 20 capacitors were used!! whereas the full projectile barley reached half the distance it did with 20 capacitors.....What is happening here????: (these measurments were taken several times (I.E. 20) and they all were considerably similar)

 

can someone enlighten me?

[swansont]

Any circuit is going to have a characteristic time, as you note, for the discharge of capacitors and also for the field build-up due to the inductance in the coil. What you may be observing is the changes in the efficiency of transforming the energy. A hollow vs solid projectile will have a different inductance. If you have some of these other values (you gave C aready) you might be able to figure out the characteristic times for an RLC circuit.

 

 

edit: don't know how much this helps, but it's an RLC simulator. http://www.oz.net/~coilgun/mark2/rlcsim.htm

 

It doesn't account for the inductance of the projectile, though