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6 Month Gauss Cannon Project

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El_Roberto

Wed Dec 31 2008, 09:42AM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
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Posts: 135

That seems to make sense to me, Blackgrunge do you think that a 8mm diameter 40mm long projectile would saturate in my 6 stage coilgun using 2Kj, and 50mm coils? I could also use 11mm at the same length but I made a small mock up of the first stage and the 8mm had far better performance. Either that or I could lengthen the projectile /coils like you say. Sounds like you have a great knowledge of the subject.

Backyard Skunkworks

Wed Dec 31 2008, 10:19AM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

The optimistic part is assuming your gun will reach 10% efficiency without endless tweaking. How ever good it all looks on paper, you generally need to tweak the thing over and over until you can squeeze every joule out of it.

The math is there to back it all up, sure. But the fickle nature of coilguns makes it quite hard to know how efficient it will be until you test it.

big5824

Wed Dec 31 2008, 12:20PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

Iv grown to believe that the graph on this page shows how saturation affects the increase in force, so once the projectile is saturated you need more and more current for a small force increase, so surely this means that having a larger projectile that doesnt saturate would increase your efficiency, as you can apply a greater force to it, thus more KE

and also, very impressive looking project, i hope it all works well :)

blackgrunge

Wed Dec 31 2008, 03:00PM

Registered Member #1889 Joined: Mon Dec 29 2008, 07:36AM
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Posts: 55

@El_Roberto

Projectile length and coil length should be the same. The only exception is if you have optical triggering. Then the first coil should be slightly smaller so that it triggers the sensor without leaving the coil because as soon as it leaves the coil it begins decelerating. For you, start with all the coils the same size and then if you want to fine tune it a bit later, play around with coil length. As far as saturation is concerned with an 8mm bore at 40mm your going to see saturation but I doubt at 2kJ you will see the maximum velocity. I personally wouldn't go any larger because every time the projectile gets bigger you are sacrificing velocity.

@Backyard Skunkworks

I completely agree. I'm assuming I'll reach 10%. I was just stating that if I reach 10% here's the results I'm going to get. But I agree that it'll be difficult to achieve.

@big5824

That graph is correct. The catch, however, is it assumes that you have unlimited energy to deal with and that you have reached maximum velocity. Just because a projectile is saturated doesn't mean its reached its maximum velocity. If and when you reach maximum velocity, increasing the projectile size will result in higher velocities as a result of a greater applied force. But I can't stress enough that shape plays a huge part in the maximum velocity. A more aerodynamic projectile will go a long way, most would be surprised of its impact.

--------

On a separate note, does anyone know where to get materials that have a higher permeability such as somewhere I could get Mu Metal that's not it sheet form. I've been looking for eons but I can't seem to find it or anything for that matter that has a higher permeability than pure iron and low carbon steel.

rp181

Wed Dec 31 2008, 07:38PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

Ahh, i see what your saying now.
Ile try to find the company i got the hymu 80 from (i got .5" rod 1ft).

What SCR's did you get?

blackgrunge

Wed Dec 31 2008, 08:31PM

Registered Member #1889 Joined: Mon Dec 29 2008, 07:36AM
Location:
Posts: 55

Haven't gotten any new SCRs yet I'm still working with the 2N5207. I called UPS and they said the caps wouldn't be here until friday :[ . But I've been looking at some 50RIA80's or 50RIA120's.

Here's a really good site if you want some of the higher end SCRs its where I'm getting mine. They make all kinds of SCRs and they are located in michigan so its easy on the shipping and handling, well at least for me.

El_Roberto

Wed Dec 31 2008, 09:27PM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
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Posts: 135

Thanks for the info, I just Remade the 8mm coilgun with a shorter coil (old one was 8cm) and the new one fired through two aluminium cans and ricoched (sp?) of the last one and missed the backplate I had and dented the wall, so I will definately stick with the smaller diameter. Also your link is broken, but doesnt it cost allot of money buying SCR's and capacitors new? I have got all my equipment off a site similar to ebay and have saved over a thousand dollars, to buy the SCR's and capacitors I have it would cost about $1500 from stores located in my country and I managed to get the lot for only $30.

blackgrunge

Wed Dec 31 2008, 11:18PM

Registered Member #1889 Joined: Mon Dec 29 2008, 07:36AM
Location:
Posts: 55

Sorry about the link for some reason these forums don't like my links.

As far as SCRs are concerned this place has new SCRs for around 10-15 dollars a piece which is really good given they can handle a 3000amp pulse. So I personally don't mind spending the extra money because I save on S&H anyways. Alltronics charged me $17!! for a $50 order!

El_Roberto

Wed Dec 31 2008, 11:47PM

Registered Member #1774 Joined: Wed Oct 22 2008, 02:51AM
Location:
Posts: 135

If you think thats bad I live in New Zealand and when I tried to order 20 of those massive electrolytic capacitors from alltronics shipping was going to be at least US$200 and for faster shipping US$400! Thats just rediculous

rp181

Wed Dec 31 2008, 11:56PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Have you actually checked the price of those SCR's? From CHTechnology (website is exactly the same as that one but with IGBT's) a 5kA surge was 110$ (ST180S12POV). I got 3 of those and destroyed them all =p
Whats your budget?
P.S. Your other link didn't work because you combined two URL's (barry's site and grandpower).

also, how old are you? want to know beacuse of the "local science competition" part.

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