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using both induction and reluctance for coilgun

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LAN_403

Quantum Singularity

Sun Apr 23 2006, 01:39AM

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

Hmm, if your barrel is conductive that could very well cause the problem. Seems like it would have the effect of shielding the projectile inside from the forces, and if the pusle was strong enough might crunch the barrel like a can crusher. I may be getting beyond my knowledge in this matter but I would think as the pulse started to grow, the flux lines would first intersect the barrel and induce current to flow around the barrel. As more flux lines pass more current is induced in the barrel and therefore a strong magnetic field begins to form that repels the flux from the coil. I am not sure how completely this would repel but my guess is very little if any magnetic flux would make it through the opposing field around the barrel and induce a significant amount into the projectile. Anyone else agree or have a different/better explanation?

FastMHz

Sun Apr 23 2006, 05:21PM

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

Thanks for the info Tristan - I do have slits cut into the side of the copper barrel to eliminate eddies to some degree, and regular steel slugs shoot out of it with lethal power...but no matter what I tried with the aluminum it just wouldn't move. I got it to budge about a mm once, but I think the coil itself jumped when I pulsed it...I haven't tried my pvc barrel yet 'cause I've been a bit busy with building my electric bazooka

Maz - I still think you should try it anyway and see what happens...it might be hard to tell if the AL part is working at all though since the steel part will work regardless...

Maz

Sun Apr 23 2006, 11:19PM

Registered Member #111 Joined: Fri Feb 10 2006, 01:04AM
Location: Menasha,Wisconsin
Posts: 65

This is basically what i was thinking. quick paint job to get a visual. i wish i could say that i have tried it but i do not have the setup for reluctance to i look forward to seeing others results!

Reaching

Fri Nov 24 2006, 10:05PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

grabbing this thread out, cause im on the search for new ideas for my big multistage coilgun.

so why not combine reluctance and induction but with 2 coils? a reluctance cg needs a longer pulse and a induction cg needs a short pulse. so i thought about it. i made a hybrid projectile with 2 sections. the head is a 3cm long 8mm steelrod the tail is a 2cm long 8mm aluminium rod held together with a iron screw inside.
why not use a simple reluctance cg coil to accelerate the projectile, then it passes a fotogate which switches the second coil on for pushing the projectile forward via induction. if it works fine it is very good for multistage coilguns cause you can use both principles. while the steel is saturating after beeing magnetized from a coil the inductive part can accelerate the whole thing. the steel part has more time to demagnetize(dont know the right word).
i hope there are no open questions, the picture is self explaining

Marko

Fri Nov 24 2006, 10:22PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

As it was discussed, when you try to launch this bullet using reluctance effect will be cancelled by attraction to iron. Maybe if you used very long projectile, with non-conducting part, or etc, but I still don't see any advantage versus using one of techniques solo.

Reaching

Sat Nov 25 2006, 02:18PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

ok, you dont understand what i was trying to explain.i want to use to seperate coils on 2 seperate coilforms to accelerate the iron part via reluctance and the aluminium part via induction. the first coil switches on and the iron is sucked into the coil, when the iron reaches the middle of the coil the first coil is turned off. the projectile leaves the first coil and passes the second coil and activates a fotogate that is placed on a calculated direction so that only the aluminium part of the projectile is in the second middle of the second coil so the aluminium part is repelled by the magnetic field of the second coil which is turned on with the fotogate. so you combined both principles. the advantage i see is that the iron part of the projectile has more time to demagnetize but still increase its velocity by the inductive part

mike0t4ever

Sat Nov 25 2006, 08:55PM

Registered Member #321 Joined: Wed Mar 15 2006, 03:33AM
Location:
Posts: 14

if you have a one coil for inductive acceleration and one coil for reluctance acceleration

then really all you fave are 2 coilguns in one your efficiency will never be the sum of efficiencies but rather the average efficiancy of each gun on its own

Reaching

Sat Nov 25 2006, 11:20PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yeah, and whats the problem? with a simple multistage cg you also have the average efficiency of both stages not the sum of both. i have to try it. the problem with a multistage cg based on reluctance is the saturation of the projectile. with a second coil based on inductance you have a chance to depolarize the projectile cause both parts of the projectile are connected electrically. so the projectile is no longer saturated , just a thought, but somewhere you have to start and why does everyone mean trying new techniques is wrong?? why not combine two techniques and use the advantages of both. for a reluctance based multistage cg the time is very important and the saturation rate of the projectile. so why do you mean it is wrong to accelerate the projectile via inductance to get a little more time for the iron part of the projectile to desaturate?? that would mean that you can add more kinetic energy in the following stages, increasing efficiency, not too much but better than nothing,

mike0t4ever

Tue Nov 28 2006, 01:36AM

Registered Member #321 Joined: Wed Mar 15 2006, 03:33AM
Location:
Posts: 14

i'm not saying it's wrong to try

what i am saying is that the additional complexity of not only the gun but also the projectile makes this a very difficult tuning problem

also an electric connection between the ferrous and Al/Cu part of the projectile will do nothing to reduce magnetic saturation problems.
it may actually increase the eddy losses on the ferrous part by giving the eddy currents a more conductive path.

i think by saturation you meant hysterisis
the only way you can reduce it is if the ferrous and conductive parts of your slug have a fair amount of coupling between them (which will reduce the efficiency of the reluctance based acceleration due to eddy currents)

WaveRider

Tue Nov 28 2006, 04:27PM

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

In my mind, there would be little benefit to using reluctance and induction effects in the same coilgun. The problems that you need to overcome are different for each.

Reluctance coilguns operate over relatively long timescales compared to induction guns. Example: Current on- times for most reluctance-based hobby coilguns: 0.5-3ms. Coil currents: 100A - 1000A. Capacitor voltages: 100-450V.

All of this is doable with readily available, relatively inexpensive SCRs, IGBTs, capacitors.

Contrast this with an induction gun: Current on-times < 10-100us. Coil currents: 5000-50000A, Capacitor voltages: 5000-25000V.

At this point, we see that given the need to switch kA currents and multiple kVs puts high levels of stress on the switching elements. It is more complicated. Switching time scales must generally be an order of magnitude shorter than for reluctance guns to reduce field penetration into the projectile (to get good force acting on the projectile).

Induction guns can generate tremendous forces (far more than reluctance guns). So if you go to the trouble of building a proper induction gun, in my opinion, it's not worth the trouble to tack on a reluctance gun...

My 2c...

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