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Navrit Bal

Fri Nov 05 2010, 11:34PM

Registered Member #3323 Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116

Using v = Vâˆš(eC/M) with your results, I get 0.5282... = 100 x âˆš ((0.01x0.012)/4.301) and the same with the equation above that...
What am I doing wrong?

Also Barry, could I list you as a source in my bibliography? If so, could you list your qualifications?

Barry

Sat Nov 06 2010, 04:11PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

I just have a minute here now, so I'll have to check the math later and get back to you. Of course I welcome others to have a look and comment.

Sure, I'd love to be in your bibliography, thanks for checking. For my qualifications, see About Barry on my website. It lists a bunch of work junk which is probably not relevant, but hopefully the MSEE degree lends some credence, even though it comes from the previous millennium.

Cheers, Barry
I'm bored so I've decided to become an evil genius and take over the world! Already got the genius thing going for me. Oh yeah, wait, got the evil thing, too!!

Navrit Bal

Sat Nov 06 2010, 04:35PM

Registered Member #3323 Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116

Thanks for letting me put you in my bibliography.
I now have 14 SWG - 2.00mm magnet wire, from Maplins. I will have to eventually wrap it around a custom plastic spool/tube, the contractive forces shouldn't be a problem at these power levels. For now, I'll leave it on the spool that it came with.

Navrit Bal

Mon Nov 08 2010, 11:23PM

Registered Member #3323 Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116

For the diodes in anti-parallel, I have 51 1N007

which allows a peak current of 1530A. I will now model my coil and pulse around this current, also I think that this is an achievable target... By the way, I'm running at 330V.

Does anyone know a rough value for E.S.R. for photoflash capacitors? Otherwise, I can never accurately account for their resistance in simulations, and then might blow something up

Barry

Wed Nov 10 2010, 03:14PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

Navrit Bal wrote ...

Using v = Vâˆš(eC/M) with your results, I get 0.5282... = 100 x âˆš ((0.01x0.012)/4.301) and the same with the equation above that...
What am I doing wrong?

The equation uses kg, not grams, so be sure to use mass of 0.04301 instead of 4.301. Also, it appears that I had a math calculation error of my own, sorry about that. Now the correct answer is 5.2 m/s or 17.1 fps.

I updated my kinetic energy web page accordingly.

Thanks for finding this! Barry
someone actually took the time to invent the word procrastination?

Navrit Bal

Wed Nov 10 2010, 07:41PM

Registered Member #3323 Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116

I knew I went wrong somewhere

and I'm glad I helped!

Could anyone offer any advice on the anti-parallel diodes? I'm going to try this tomorrow at ~2-4PM, that's when my allotted time is.

Also, could you use anther coil to effectively reverse the negative initial pulse?
If not, could you use something that somehow discriminates between positive and negative voltages and allows them to different parts of the circuit depending on the polarity? (+ goes back to the capacitors, - goes elsewhere)

Navrit Bal

Wed Nov 10 2010, 10:36PM

Registered Member #3323 Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116

Also Barry, with your "t = 2d/v" equation mentioned, what is 'd'. Based on what you had there, is it the coil length?

Barry

Thu Nov 11 2010, 12:08AM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

Navrit Bal wrote ...

Also Barry, with your "t = 2d/v" equation mentioned, what is 'd'. Based on what you had there, is it the coil length?

On the Estimating Timing page, "t = 2d/v" will give us a very crude estimate of the time it takes for the projectile to move from its starting position (at rest) to the point where acceleration ends.

In most coilguns, the projectile is about the same length as the coil, and you can use d = coil length = projectile length = distance over which it is accelerated.

In other words, the projectile begins acceleration where the tip enters the coil, and ends acceleration when the projectile is centered and its tip is just about to exit the coil's other end.

If you had a much longer or shorter projectile, you'll have to look at your geometry and take a guess at what points you think movement will begin, and acceleration will end. For example, if you shoot an iron pellet (like a BB) using a long coil, the distance 'd' starts at the coil entrance and ends after the pellet has moved a short ways into the coil (about the length of the coil's inside diameter). This acknowledges the fact that the magnetic field is essentially uniform once things are well inside. To be certain would require knowing the force profile as a function of position.

Hope this helps! Barry
If at first you don't succeed, find out if the loser gets anything.

Saz43

Thu Nov 11 2010, 12:11AM

Registered Member #1525 Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294

Navrit Bal wrote ...

I knew I went wrong somewhere

I can't comment on the use of another coil to absorb the negative pulse, but my intuition tells me that it would be difficult to do. Do you mean have it set up somehow like a transformer where the secondary absorbs the energy of the collapsing field of the primary? It certainly wont "reverse" the negative spike, that's for sure.

There IS a circuit that can direct the negative pulse back into the capacitor banks at the proper polarity, called the half-bridge. Here is a very successful coilgun that uses it:

For the commutation diode, if you're using an SCR switch, the diode just has to handle the peak reverse current (as found using Barry's RLC simulator).

Navrit Bal

Thu Nov 11 2010, 10:12PM

Registered Member #3323 Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116

I was just asking about anything like them, and the half-bridge might be the solution!

As I said, I have a Toshiba mg100q2ys42

and I just realised, has a half bridge built in!
Although, I don't know which terminals I would use for what... an explanation or a little help would be great. Am I reading correctly that it takes 200A over 1ms?

Also, I soldered the diode array today of all 51 1N007s, soldered together and with a copper wire woven through it. 6ghimu

The Coil : 11izmma

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