using both induction and reluctance for coilgun / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

using both induction and reluctance for coilgun

previous 1 2 3 4 next

Move Thread

LAN_403

Electroholic

Wed Apr 19 2006, 04:56AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

Care to Explain more?
What is the bullet placement? before or after the coil?
Which is head, which is tail?
Steel / Alu?
How do you pulse the coil? single / multi pulse?

If you are using only single pulse,
while bullet placement is behind the coil,
with steel as head, Alu as the tail.
I would imagin that when the steel part got pull into the coil, the alu part will be repelled.
You will lost energy and break your hybrid bullet.

the only way for it to work is like Madgyver have said.
longer spacer.
and you still have to pulse it twice.
still don't think efficiency would increase tho.

evilgecko

Wed Apr 19 2006, 06:58AM

Registered Member #288 Joined: Mon Mar 06 2006, 07:52AM
Location: Palmerston North
Posts: 32

If you had iron to the left of the center of the coil, and then aluminium to the right, then both forces would be in the same direction, accelerating the bullet to the right.

Electroholic

Wed Apr 19 2006, 07:06AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

Oh!

I'm dumb.

humm...I bet suck back is serious issue there then.
Then middle section will have to be tuned to the pulse length...

FastMHz

Thu Apr 20 2006, 08:56PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

I just took one of my good CG coils and put an aluminum nail in it and fired it...nothing happened whatsoever...which surprises me, since my induction launchers work so well...maybe it cancels itself out and firing a non-ferrious slug from a cylindrical coil just won't work.

GimpyJoe

Fri Apr 21 2006, 02:53AM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Have you tried playing around with the projectile starting position?

WaveRider

Fri Apr 21 2006, 08:48AM

Registered Member #29 Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500

Starting position is important. Remember that the induction coilgun relies on repulsion of the armature instead of attraction, as in a reluctance coilgun.

Generally, a coilgun designed as for use with ferrous armatures will not work very well with non-ferrous materials. Induction guns need firing pulses at least an order of magnitude (two orders are better) shorter than reluctance guns. As a consequence, higher coil currents are required to generate the proportionally higher instantaneous forces over these short times...this means high voltages and high currents, e.g. kV and 10s of kA, typically. (The dynamics are similar for can-crushers and ring launchers.)

The pulse times must be short enough that the currents induced on the surface of the armature do not have time to penetrate and decay significantly during the firing pulse. Once the currents decay and the magnetic field fully penetrates the armature, the forces vanish.

You can get an order of magnitude idea of the relationship between penetration depth and pulse time from the "skin-depth" formula

x_p = sqrt{t_p / (mu_0 * sigma)}

where x_p is the desired penetration depth (which should be a small fraction of the armature radius), t_p is the permissible pulse duration, mu_0 is the vacuum permeability (4e+07 * pi H/m in SI units) and sigma is the armature conductivity (3.767e+07 S/m for aluminium in SI units).

Ferrous armatures do not have this built-in pulse time limitation. It's enough to switch off the current before the slug starts to exit the coil.

There may be room for building a "linear induction motor" that uses windings on a ferrous armature.....Hmmmm <scratches head....>

TheMerovingian

Fri Apr 21 2006, 09:58AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

I think that the two approaches cannot be used at the same time. For a simple reason:
Induction coilgun needs fast rise/fall rates (since it relies on eddy currents). The iron part of the projectile is also conductive and will be repelled. Probably less than the other side due to the skin effect as you have stated but still present, reducing the advantage. Other problem is that coilguns don't work very well with fast pulses, because if higher inertia of the projectile (alu is lighter). And you risk the current falling way before the projectile reaches the critical point wasting power. Another risk is the detachment of the two sections since the forces are not the same (in the rise-phase of the pulse the alu-section will be repelled more that the attraction of the iron core).

I'm don't saying it is impossibile, just overcomplicated and overdangerous (High voltages, no semiconductor switching, difficulty to multistage it etc)

FastMHz

Fri Apr 21 2006, 06:18PM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Yes I tried putting the AL nail in every position I could with no effect. I used the same cap bank I used for my induction launchers, and the CG coil is the same length of the same wire that I made my pancake coils with - so the pulse length should be similarly short. The nail doesn't even budge, not even by a hair...I hope somebody else tries it to see if the results are the same...there's really no point in making a dual induction/repulsion lanucher if aluminum can't be fired from a CG.

Quantum Singularity

Fri Apr 21 2006, 07:30PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Got to be a problem with your setup fastMHZ...

there's really no point in making a dual induction/repulsion lanucher if aluminum can't be fired from a CG.

Pulslaser (and others too) made a pretty awsome induct/repulsion cg that I beleive fired both solid and hollow aluminum rounds. It is down the list a little ways:http://4hv.org/e107_plugins/forum/forum_viewtopic.php?2913

Not sure if I have an answer why yours isnt working... maybe its just so far out of tune? And I know you probably tried this but as far as start position the projectile should probably be entirely to one side off center of the coil, if not further out. I would think if very much of the projectile crosses center than it will cancel out.

For the original poster... my 2 cents on the combo gun would be that it is an interesting idea and would be unique however I would think the efficiency would be less for sure. The two types are too far apart to be used together efficiently. It would be more efficient just to make an optimally designed cg that used 2 stages rather than a compromised cg that used 1 stage but 2 different forces. Remember the reluctance gun can utilize more of a steady state current through the coil to draw the projectile in (the limit being when the projectile reaches center) and the induction/repulsion utilizes fast rise times to induce eddy currents (which is what creates the force). Thats just a simplistic view of the differences but shows just how different they are.

FastMHz

Sat Apr 22 2006, 12:53AM

Registered Member #179 Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287

Interesting...I'll go do more experimenting...maybe my barrel being copper is a problem or something, so I'll try one of my coils on PVC with the AL nail and see what happens. I don't think I tried putting the nail entirely out of the coil either. I'll post back after I do some more testing.

previous 1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob