EM Gun - Trying to understand schematic

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Bob Scott
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Post by Bob Scott » Tue Mar 18, 2008 4:48 am

Robert Reed wrote:Bob
A little off topic, but why did you change your avatar? I loved the old one, you big chicken you. :grin:
Here, you can use Marv from Sin City II as your avatar. :grin:

Image

I got him from http://www.theempire.com.au/images/2006 ... Figure.jpg

Bigglez
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Re: EM Gun - Trying to understand schematic

Post by Bigglez » Tue Mar 18, 2008 10:01 am

Greetings all,
Bigglez wrote:I was flipping through the March 2008 Nuts
and Volts and saw the article about an electronic weapon.
I'm trying to understand the schematic, Figure 2.
What is the function of SW2? What are D5 and D7 for?
What does the CR circuit (R13,C7) do?
What is D8 for?
When I revisted this thread this morning I realized that
we're drifted away from my OP (above). No one is to
blame, as I as much as anyone else has taken shots at
the published circuit and design.

In trying to answer my own question for myself, and
with help from the author and others that have posted,
I have a much better understanding of the original
goals and experimental work behind the weapon.

While weapons aren't my "thing", I do find this topic
interesting, and I'd like to continue the discussion.

I'm suggesting that I start a new thread, for open
comments on the theory and construction of a
similar weapon (or coil launcher if you prefer).
This thread should really be about my original
struggle to understand what has been presented,
rather than a continuing critique.

I don't doubt the author built and operated the
weapon, and that others with construction skills
would not be able to follow the plans and build
their own.

Anyone agree, disagree, what to drop it and move on?

Comments Welcome!

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MrAl
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Post by MrAl » Tue Mar 18, 2008 11:27 am

Hi again Peter,


I just want to clarify one thing, that with my posts i was not taking
'shots' at the circuit (as if target practice <chuckle>) but merely
trying to help improve the circuit as much as possible. I do this
with many other circuits too and so i treat this circuit as a
prototype with some loose ends.

I think it would be great to start another thread where we can
talk about another design, with a different driver etc. and maybe
someone can build one up.

BTW, in the original article is there anywhere where it mentions
what kind of transformer metal is being used for the transformer
core, and where to purchase it too maybe?
LEDs vs Bulbs, LEDs are winning.

Bigglez
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Post by Bigglez » Tue Mar 18, 2008 12:50 pm

Greetings Mrai,
MrAl wrote:BTW, in the original article is there anywhere where it mentions
what kind of transformer metal is being used for the transformer
core, and where to purchase it too maybe?
If you have a birthday coming up you might drop
some hints for a Nuts and Volts subscription...

The transformer for the project was custom made by
the author, who gave construction details (also on
his web page cited earlier, with PIX).

The novel approach was to salvage the bobbin and
cores from a CF (compact Fluorescent) ballast.

When this hobby was more about "wireless", coil
winding was a necessary homebrew skill. I don't
think there are many of us that have stocks of
magnet wire, a coil winder, and a decent LCR bridge.
Not to mention that access to cores and bobbins
is a bit of a problem, too.

Comments Welcome!

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philba
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Post by philba » Tue Mar 18, 2008 1:42 pm

Bigglez wrote: When this hobby was more about "wireless", coil
winding was a necessary homebrew skill. I don't
think there are many of us that have stocks of
magnet wire, a coil winder, and a decent LCR bridge.
Not to mention that access to cores and bobbins
is a bit of a problem, too.

Comments Welcome!
This reminds me how stupid I can be. About a year ago a local motor winding shop was going out of business. The guy put his entire stock of wire on craigs list and I didn't go for it. He had spools of 10 different gauges and a couple of winders. I heard later that the guy sold the wire for scrap because he got NO TAKERS. Arrrrggggggghhhhhhh

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Karl Williams
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Open source coilgun project?

Post by Karl Williams » Tue Mar 18, 2008 1:47 pm

Hi All,

Maybe we could get an "Open Source" type of coilgun project going based on a popular microcontroller that we all agree on?

People could submit ideas and then a few of us could breadboard and debug as we go...

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Re: Open source coilgun project?

Post by Bigglez » Tue Mar 18, 2008 2:32 pm

Greetings Karl,
Karl Williams wrote:Hi All,

Maybe we could get an "Open Source" type of coilgun project going based on a popular microcontroller that we all agree on?

People could submit ideas and then a few of us could breadboard and debug as we go...
Sure! Although I think it's an analogue intense
project, with minimal uC involvement.

You can jump start us with a preliminary goal
or spec. Are you trying to improve the EM-15,
and use the same mechanicals, or is this a
fresh start?

How did you arrive at 300j energy? Is this a
practical limitation, a result of known materials,
or the outcome of some bench testing?

The project has two challenges; namely;
charging the capacitor(s) quickly and safely,
and dumping the charge into kinetic energy
to shoot the projectile.

Or, did I jump to conclusions?

Comments Welcome!

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Bob Scott
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Re: Open source coilgun project?

Post by Bob Scott » Tue Mar 18, 2008 3:10 pm

Bigglez wrote:How did you arrive at 300j energy? Is this a
practical limitation, a result of known materials,
or the outcome of some bench testing?
I'll bet N&V published the article because the "weapon" looked good but was low power. After looking at the author's video, I saw another video suggestion pop on screen with a more dangerous 2,500 joule device.

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haklesup
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Post by haklesup » Tue Mar 18, 2008 3:18 pm

Karl, it looks like you have a great opportunity to not only improve the design "open source" style but a followup article on Rev 2 and your experiences and engineering thought process would useful from many angles.

(muse) A good article shows the circuit and explains the operation and construction but a great article gets inside the designers head and explains why the choices were made (and what those other choices were and why they were not chosen) so the reader can actually pick up where you left off. (even if the reasons were mundane)

WRT the uController concept, what functions do you see as being digitally driven. Would you go so far as to drive a charge pump (substitute the bipolar oscillator you currently have) with the digital I/O pins. For example, a square wave filtered to a sine then buffered through an audio amp and applied to the transformer primary. you could program the frequency and duty cycle on the fly. This makes the project like a demo board where a user can try other settings than the designers optimal choice.

At the simpler end, the uC could function to operate the switches, measure the HV (instead of the comparitor) and run some sort of LCD display with basic status. On a more complex side a uC could synchronize the firing of a multi coil launch rail and allow reconfiguration of said timing through menu driven display and some user buttons. With A/D and D/A capibility the HV preset could also be programmable. How far do you want to go?

For the purpose of project management, I might suggest that it be broken into the following segments, you may see a better way to break it up.

Specifications and operating parameters
Block Diagram
User Interface
HV source
Trigger section
Charge storage and coil driver
Component selection review and BOM
Packaging and Assembly issues


At each step a contribution might include:

Schematic fragment
Simulation of subcircuit or validation
Component donations
Firmware Code, device programming
Prototype assembly
Electrical charactrization / test
Documentation

Bigglez
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Post by Bigglez » Tue Mar 18, 2008 9:16 pm

Greetings Phil.
philba wrote:This reminds me how stupid I can be. About a year ago a local motor winding shop was going out of business. The guy put his entire stock of wire on craigs list and I didn't go for it. He had spools of 10 different gauges and a couple of winders. I heard later that the guy sold the wire for scrap because he got NO TAKERS. Arrrrggggggghhhhhhh
Too bad... (I think we've all been there or somewhere close).

For small coils and transformers the "Morris" coil
winder is popular and shows up on eBay from
time to time. I found a made in China motor coil
winder (via Hong Kong) on eBay for about $30,
and it's a great improvement over my
"bobbin on a pencil" hand winding technique.

As for magnet wire, I have a few open reels from
the scrap bin of a former employer. The kicker is
that when you work around abundant scrap (of any
kind) it looses value and the novelty wears off
quickly. Only after I moved on did I realize I left
a lot of mag wire useful for a hobby but otherwise
worthless scrap in the recycling bin!

Comments Welcome!

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MrAl
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Post by MrAl » Wed Mar 19, 2008 5:54 am

Hi again,

I think that an open source project would be cool too.
I also agree that this is more of an analog project, but a uC
controller would be interesting too, probably using a PIC.
I think that two versions...one with a PIC and one without a PIC
would be a good idea because some people dont want to get
involved with uC'ers. The non uC version would appeal to people
who would just like to get back to a pure analog design too.

We also need at least one volunteer who would like to build this
up and test it.
LEDs vs Bulbs, LEDs are winning.

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