RC-Monster Forums  
RC Monster

Go Back   RC-Monster Forums > Support Forums > Project "X"

Reply
 
Thread Tools Rate Thread Display Modes
Need some advice...
Old
  (#1)
What's_nitro?
Soldermaster Extraordinaire
 
What's_nitro?'s Avatar
 
Offline
Posts: 4,529
Join Date: Apr 2007
Location: Plymouth, MA, USA
Arrow Need some advice... - 07.31.2011, 01:59 AM

How many of you have built a coil gun???

I need some advice and/or guidance from the electrical engineers in the group. I have a pretty solid understanding of electronic design, but I often find myself second-guessing my layouts. I think having some other eyes on this would be helpful since my prototyping budget doesn't allow for many burned components...

Attached is a full schematic of the system I have in mind. I've gone over it several times trying to follow all the possible current paths and make sure there are no shorts, or any other undesired electrical activities.

The 20-30vdc supply is via an 8-cell A123 battery pack. The 300-450vdc is provided by a power inverter/voltage multiplier combo, which gets its power from the A123 pack. The "projectile sense" switch is a lever-actuated microswitch, located in the barrel ahead of the firing coil, and arms the gun when it is loaded while lighting an LED as indication. Resistor R3 is in place to keep the base of Q1 negative biased until the "fire" button is pressed. Capacitor C2 is charged to a potential of 10-18vdc, depending on the potential of C3-C5, by a voltage divider consisting of R6-R7. When the "fire" button is pressed, C1 discharges through R2 into the base of Q1, turning it on, which allows C2 to discharge into the base of Q2, which turns on, allowing C3-C5 to discharge through Q2 and L1. When the projectile has moved through L1 far enough to depress the "projectile sense" microswitch, the base of Q1 is again negative biased, turning it off. Q1 turning off then allows the base of Q2 to become negative biased once again through R5, halting the flow of current through L1. The residual EMF in L1 is shunted through D2, preventing any tug-back on the projectile and also protecting Q2 from transient voltage spikes.

At least, that's how it should work.
Attached Thumbnails
Click image for larger version

Name:	SSCGS.jpg
Views:	167
Size:	28.6 KB
ID:	10095  


I am faster than Buzz Lightyear.
   
Reply With Quote
Old
  (#2)
suicideneil
They've been naughty boys, havent they Mr. Flibble
 
suicideneil's Avatar
 
Offline
Posts: 7,491
Join Date: Feb 2007
Location: Devon, England
07.31.2011, 10:22 AM

Pass.

I've watched a few videos of guys who've made these things, and they do always look awesome, but I can't help thinking how pathetically underpowered and pointless they are too. I mean, the efficiency is about 4% or so- the projectiles look killer but you could do more damage with a modified nerf gun or airsoft, let alone an airgun.

Just seems like a massive amount of effort and expense to build something that has such poor power and range & which you would quickly get bored of as a result; buy an airsoft rifle or pistol and dress it up = much cooler.

This guy made a cool mains powered one, just incase you haven't seen it- he published his schematics too:

http://www.megavolts.nl/en/projecten/geweren/46-megagun
  Send a message via MSN to suicideneil  
Reply With Quote
Old
  (#3)
What's_nitro?
Soldermaster Extraordinaire
 
What's_nitro?'s Avatar
 
Offline
Posts: 4,529
Join Date: Apr 2007
Location: Plymouth, MA, USA
07.31.2011, 02:29 PM

I have seen that, Neil. I think I've seen just about every coil/rail gun project on the net. I know they aren't very efficient but I have some ideas about that which I haven't seen used in any of the designs on the net.


I am faster than Buzz Lightyear.
   
Reply With Quote
Old
  (#4)
What's_nitro?
Soldermaster Extraordinaire
 
What's_nitro?'s Avatar
 
Offline
Posts: 4,529
Join Date: Apr 2007
Location: Plymouth, MA, USA
08.02.2011, 02:05 PM

Bump?


I am faster than Buzz Lightyear.
   
Reply With Quote
Old
  (#5)
BrianG
RC-Monster Admin
 
BrianG's Avatar
 
Offline
Posts: 14,609
Join Date: Nov 2005
Location: Des Moines, IA
08.02.2011, 02:17 PM

Couple of things:

I hope you plan to use a Schottky diode for your back-EMF protection. Otherwise, it might not shunt the emf quick enough to protect your transistor and/or power source. Also, make sure Q2 has a C-E voltage of at least 500v.

How about using an optical switch instead of mechanical. Purely for reliability from a mechanical standpoint; just an LED and photosensor that triggers when the projectile breaks the beam.
  Send a message via Yahoo to BrianG Send a message via MSN to BrianG  
Reply With Quote
Old
  (#6)
What's_nitro?
Soldermaster Extraordinaire
 
What's_nitro?'s Avatar
 
Offline
Posts: 4,529
Join Date: Apr 2007
Location: Plymouth, MA, USA
08.02.2011, 02:45 PM

Thanks for your input, BG.

I attached the datasheets for what I had in mind for Q2 and the protection diodes.

The transistors have a C-E voltage of 1000V max, but the EMF will probably exceed that value so that's why the diode is still there.

The diodes are 1200V, 7.5kHZ; so <70uS response time. I was just thinking it may make sense to have a diode on the collector side as well to prevent the caps from being charged in reverse.

As far as mechanical vs. optical trigger, I'm still on the fence about it.
Attached Files
File Type: pdf QM200HA-2H.pdf (68.5 KB, 120 views)
File Type: pdf IN3296.pdf (554.5 KB, 146 views)


I am faster than Buzz Lightyear.

Last edited by What's_nitro?; 08.02.2011 at 02:52 PM.
   
Reply With Quote
I fell off the fence. :)
Old
  (#7)
What's_nitro?
Soldermaster Extraordinaire
 
What's_nitro?'s Avatar
 
Offline
Posts: 4,529
Join Date: Apr 2007
Location: Plymouth, MA, USA
I fell off the fence. :) - 08.06.2011, 12:45 AM

On to what appears to be the right side based on my new, freshly revised, schematic.

I decided to go with an optical trigger on the projectile, as well as opto-isolation for the HV side of the circuit.



I am faster than Buzz Lightyear.

Last edited by What's_nitro?; 08.06.2011 at 12:54 AM.
   
Reply With Quote
Old
  (#8)
What's_nitro?
Soldermaster Extraordinaire
 
What's_nitro?'s Avatar
 
Offline
Posts: 4,529
Join Date: Apr 2007
Location: Plymouth, MA, USA
08.06.2011, 12:49 AM

If anyone would like a circuit breakdown, I'll write it tomorrow.....too tired to do it right now.


I am faster than Buzz Lightyear.
   
Reply With Quote
Old
  (#9)
brainanator
RC-Monster Aluminum
 
brainanator's Avatar
 
Offline
Posts: 738
Join Date: Oct 2010
Location: Williston, ND
08.06.2011, 02:13 AM

this is some really cool stuff. Any idea what you're making the housing out of?


OFNA Jammin CRT.5e, Savage Flux HP, MBX5Te, SCX10, Multirotors, foam planes
  Send a message via Yahoo to brainanator Send a message via MSN to brainanator  
Reply With Quote
Old
  (#10)
What's_nitro?
Soldermaster Extraordinaire
 
What's_nitro?'s Avatar
 
Offline
Posts: 4,529
Join Date: Apr 2007
Location: Plymouth, MA, USA
08.06.2011, 11:31 AM

I actually have the shell of a nerf gun that I think it could be built into, sans the gigantic main capacitor.

I'll probably make the housing from polycarbonate since I have a good stock of it already. The circuit in the picture will fit onto a small (2"x3") PCB, which is nice because that will keep everything neat.

A small tip on the schematic- The pink lines represent the barrel of the gun. The zener diodes keep the system operating at exactly 12V to guarantee consistent operation.


I am faster than Buzz Lightyear.
   
Reply With Quote
Old
  (#11)
What's_nitro?
Soldermaster Extraordinaire
 
What's_nitro?'s Avatar
 
Offline
Posts: 4,529
Join Date: Apr 2007
Location: Plymouth, MA, USA
08.07.2011, 04:34 AM

Revised.........again.

Now with component values!

...and the Zener diodes are correctly polarized!



Component selection is based in part on what I have in my inventory. If you can think of a more suitable component please let me know.




Also... 784 views with only 10 replies, 7 of them my own... Must be the Google bots.


I am faster than Buzz Lightyear.

Last edited by What's_nitro?; 08.07.2011 at 04:40 AM.
   
Reply With Quote
Old
  (#12)
Semi Pro
RC-Monster Titanium
 
Semi Pro's Avatar
 
Offline
Posts: 1,402
Join Date: Aug 2008
Location: Twin Citys Mn
08.07.2011, 04:58 PM

im interested but its alittle over my head to be honest


Quote:
Originally Posted by Semi Pro View Post
......maybe they want to be more like novak
Quote:
Originally Posted by BrianG View Post
I'm telling Patrick you said that!
   
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump



RC Monster




Powered by vBulletin® Version 3.8.1
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
vBulletin Skin developed by: vBStyles.com