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V3 Coil Carbine

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DerAlbi

Wed Oct 09 2013, 11:02PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Current waveform is... fuck it. Not worth asking the question. its answered many times already. its all out there.
google: "inductor resistance current"
second link:

That was hard. i know.

Paralleling mosfets is not as complex as paralleling IGBTS. But really.. are you kidding me, that you wait for an answer here?
-> Google. "paralleling mosfets"
First hit:

Including causes of imbalance and solutions.

Boy... are you living in china? i think yahoo is capable of searching the internet too.

ben5017

Thu Oct 10 2013, 12:11AM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

YOU ARE NOT FORCED TO READ/RESPOND TO MY POSTS

DerAlbi

Thu Oct 10 2013, 12:39AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

no, but how else to show you that you are better off with stopping to ignore all the answers to your questions. They are there. you are not doing anything fancy. its done before. many times. you struggle with basics. this is explained everywhere.
its mostly about using the keywords or alternative words of a question.
Its the most important thing to learn.. how to learn. trust me.

ben5017

Thu Oct 10 2013, 01:11AM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

I told you this was my first serious electronics project I AM LEARNING THE BASICS. And I never claimed this project was "fancy". The project goals were to make something with my new cnc router, learn to program Arduino, and learn basic electronic design. By the end of the build , whenever that is I will have accomplished all 3

if you do not like my build YOU ARE NOT FORCED TO READ/RESPOND TO MY POSTS

DerAlbi

Thu Oct 10 2013, 02:22AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

how old are you?

Yandersen

Thu Oct 10 2013, 10:33AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

He is an American, Albi...
Easy, Benny. Learning can be done individually by using google and it is more efficient, fast and reliable then asking on forums. And learning cnc before understanding the basics of electronics is... seems to be the same nonsence as switching off coils at 600V having 24V for switch on. It is like building the cage of the gun having no guts solidly optimised... And so on.

As for MOSFETs, the devices you should have used instead of IGBT, the paralleling is as simple as putting the devices as close to each other as possible connecting the pins in parallel. But there are plenty of good 100V MOSFETs available which will perform perfectly alone (see my links again, or you can ask me to search digikey for you for the devices with required parameters).

"Coil Inductance plays a larger role than resistance in limiting the current true?"

Not in your design - you limit the current by coil's resistance, right? The speed of current rise is inversely proportional to inductance and proportional to applied voltage, which is the source voltage minus the voltage drop on the switch and minus the coil's resistance multiplied by current. So the higher the current, the slower it rises. When coils shut off, the speed of current fall is proportional to the zener voltage plus resistance*current - so resistance plays controversal here, see? As result, with 24V on input and 24V on zeners you will have current decaying faster then it was rising. That is why 600V is nonsence and 100V MOSFETs is the top devices for your application, even though 60V ones would be awesome too.

And BTW, as MOSFETs can handle higher pulse currents, you can achieve higher speed, but you need a cap in parallel to battery for that. Shorting the projectile and coils 2-3 times would let you achieve that as well as higher efficiency.

Steve Conner

Thu Oct 10 2013, 11:11AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

First of all...

site rules wrote ...

Part I: Behavior and Conduct
A. Be respectful. This includes everyone: other members of the forum, moderators and administrators, other people on the internet, and any other person, living or dead. Making false statements that are damaging to another person's reputation is not allowed. Insults, threats, and harassment are prohibited!

site rules wrote ...

Part II: Posting
B. Do your own research. If you intend to ask a question, please make sure it isn't already addressed in the archives, or on the wiki. Also, be sure to perform at least a cursory Google search. Remember, nobody wants to do your homework for you. Show some effort, and the community will repay you in kind.

Now onto the science... Coilguns are pretty inefficient so it hardly matters how you drive them in practice. But in theory, the most efficient way is probably to drive from a supply of several hundred volts and use IGBTs in an energy recovery scheme such as the diagonal half-bridge. You minimise suck-back by turning the drive off early and allowing the coil current to decay through the energy recovery circuit. If the coil resistance was negligible, you would shut the drive off when the projectile was about halfway in.

Try Barry's coilgun simulator to get a feel for the way things interact.

ben5017

Thu Oct 10 2013, 01:23PM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

"He is an American, Albi..." And proud of it (albeit a little less lately.., say the last 5 yrs or so...)

I Forgot you Eastern Europeans are so superior to us westerners HAHAHA

-26 yrs old, I don't know why that matters but ill play along

ben5017

Thu Oct 10 2013, 06:10PM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

ben5017

Wed Sept 16 2015, 04:39PM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

Worked on the V3 for the first time in months and finally have some performance data to share

Changed battery to 12s 3.7 AH lipo

performance data:
115 ft/s
32g slug
19j KE

drum mag is still work in progress
I am reading the encoder with the Arduino, but have not written the control code yet.

more updates to come when I find time to work on her some more.

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