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Fully Automatic Stationary Gun

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Author Topic: Fully Automatic Stationary Gun  (Read 301 times)
Man of Insane Mods.
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« on: August 29, 2007, 12:59:41 am »

Okay as promised, here's the write-up for the F.A.S.G (Thank God I called it "stationary", lol)

1st off I'd like to thank anders for giving the most bashed gun a chance (MT20)
He turned a semi-automatic gun (That jammed like no tomorrow), into a "beautiful" 8 round fully automatic war machine that was just so inspirational.
I used a lot of the advice he gave (because he actually knows what he's doing), and added a few tweaks of my own.

The difficulity isn't not high at all, I'm pretty sure anyone can build one if they follow the diagrams.

Items needed:

Wood -   (x1) 1/4" x 2 1/5" x 3'
   (x1) 1/4" x 5" x 2'

(x2) I recommend Longshot front gun triggers (try to buy it from another member since hardly anyone uses that weak
   gun, and a lot of members just integrate the front gun into the LS so their triggers are just collecting dust).
   If you can't get your hands on a pair of LSFG triggers, then I suppose you could substitute with pull strings.

The motors from a Mech Tommy 20 gun.

The wires and the normally open connection from a Mech Tommy 20.

The metal pieces from the battery compartment of a Mech Tommy 20 and a Nite Finder.

A switch (Can be a button switch, light switch, turn switch, or like myself- a busted computer fan switch)

Copper/metal wires.

The Normally Open connection from a NF (The metal piece behind the trigger that completes the circuit and turns on
   the lazer.)

A bunch of really thin cardboard, 8 1/2" x 14" (I got these from my office. They come with the stacks of  printing paper.)

1' of 1/2" PVC

A handful of screws (Left over Nerf guns screws is best)


Wood glue

Rotary tool/Dremel

Hotglue Gun+Hotglue

Optional piece(s):

The lazer from a NF

A pair of Door Hinges (They're usually sold in pairs from any hardware store for $2-$3)

A tripod (They sell these at Radio Shack from $30-$40, but you can use a kid's telescope tripod like I did.)

(x4) 2' x 3' (or larger) cardboard

(x2) Hefty or strong garbage bags (You could use really thin styrofoam, but it's easier to obtain several square feet of garbage bags.)

A handful of Popsicle sticks

(x6) Binder Clips (Medium - Large sized)

(x4) 3/16" - 1/4" screws

(x4) Washers (With an ID large enough to fit the 4 screws above)

The Battery storage pack

You can use the MT20's battery storage pack if you want, it might actually save you time since everything's done for you and you'd just have to cut out the square frame of it.


If you want to do it my way...

MT20 Motors

Just be careful when taking the motor out of the MT20.
When it's out there's very little modding needed to be done. Just sand down any nudges that juts out and might interfere with the frame of your gun, etc.
The 2 motors were designed to work with 3 AA batteries, (4.5 volts) but you can do as I did and push it up to 4 AA's (6volts). The speed of the spin of the motors works as you might think... more volts/power = faster spin. But growing up watching Home Improvement... more power =/= better/safer. Anders made his operate with just 4 AA's and I agree. Some of you suggest using a 9V battery which is much simpler to hook up to the motor, but doing that will kill your motors over extended use (I hooked it up to a 9V battery to see for myself, and it did spin a little bit faster/louder, but risking 2 motors to do it was not worth it. So just take Ander's and my advice, and STICK WITH JUST 6 VOLTS TOPS!!

For the wheels, I suggest wrapping a few layers of E-tape around them for a batter grasp.

The Dart Propelling Motor

I used a toy race track motor to propell my darts forward because it was all assembled for me. It was basically the same motor used in the MT20's (or hand held fans), hooked up to some gears connected to a rubber wheel. The motor I used had a small gear connecting to a larger gear, which meant that it actually spun the wheel much slower then the motor spun. If you want to make your own propelling wheel, connect the wheel directly to the motor. The wheel can be made out of anything... even a Gatorade cap with some E-tape wrapped around it.

The Internal Wirings

For those of you that have never worked with electricity before, either get an expert to help you or an adult will usually suffice.
ALL EXPOSED WIRING MUST BE SEALED!! Use wire connectors to connect wires if you have (ask your dad, most likely he'll have a few packs). Go to a store and buy them... they've only a few bucks for a pack,... but if you are that cheap and don't care about risking exposed electricity, as a last resort, atleast cover your connected wires with a few layers of E-tape.

It's been a while since I've had to draw circuit diagrams so please bare with me...

Some of you might be wondering why I didn't ust connect the 3 motors to a single power supply... well I did... at first. When I was building the prototype, I had 6 volts of batteries all powering everything, and it seemed fine at first. Then when I loaded one of the prototype cartridges into the holder, the darts jammed (surprise surprise... a prototype having bugs). That showed me something else that was going to be a problem, when the darts jammed (too much weight for the wheel to handle), the wheel struggled to spin, and it exerted more and more energy to do it, which drained the energy going into the 2 MT20 motors. That was when I realized I needed a second power source, that way I can run 3 volts into a single motor, which gave it a hell of a lot more spinning power to propel the darts forward.

The Frame of the Gun

Think "Shoe box" when trying to imagine the frame of the gun, because that's what mine came out as. Sure if you have a bunch of free time, you can design a super cool frame, but I'm all about simplicity (at least for this build, I am).
There's really no super hard work for making the frame, except physical hard work... hacking/sawing the wood. If you have access to a miter saw or a table saw... then I envy you, because I did all the major cutting by hand... and only the small cuts by rotary tool.

The Measurements of the Cartridges, and the Holder that grabs onto the cartridge

Those thing I leave to you do decide because it's based on the dimensions of your darts.
Make sure when you're making the folds on your cardboards, that you'll leave enough room on the sides of the darts so they wont get stuck inside, each dart must be able to freely drop from the top to the bottom with no resistance (I recommend the space between the dart and the wall of the cartridge to be 1/16", Front to Back; Side to Side)
The Holder should grab onto the cartridge just right, NOT too tight, and NOT too loose. You could do as I did if it's too loose. Cut slits on the top of the holders where the ends of the cartridges would be, and insert a popsicle stick into the slit to grab onto the cartridge (See pics for reference).

Placement of the Clip/Clip Holder

This part is probably the most important part. It took me a week and a half to figure out why the ROF was so erratic. One moment it was spitting out everything in under 3 sec which sucked because the darts only went 6'... the next, it would have a 5 sec gap between shots, which allowed the motor to get back to speed, but the ROF was crap...
It was near the end of the mod when I realized that the position of the clips determined the ROF. If you placed the clip farther back, so that the wheel would touch the head of the darts, then you'll have a SUPER HIGH ROF (I mean 26 darts in under 3 sec), if you place it so that the dart's mid section touches the wheel... the wheel would have to spin a few times to drag the dart forward enough to be propelled. So just do some test run until you find your own "sweet spot" (where you get the greatest ROF but don't sacrifice too much distance).

Adding a Tripod

Since not everyone has a tripod, or have similar tripods... I'll have to leave it up to you to determine how to attach it. For myself, I used some door hinges and screwed it to the belly of the gun, that way, if I were to store it away, the flaps would be able to fold up (See pics for reference).

Super Shields

This is not really required... but it's a great advantage if you're up against Titan users in "capture the flag" games.
The garbage bags is just 1 material you can put between the 2 layers of cardboard, you can put anything lightweight in it... like bubble wrap, silk... etc.
Besides making the shields anti-armor piercing, you can also take advantage of the large size of it, and attach clips to the walls facing you. Just attach some 1LB magnets to the walls and tape some washers to the sides of clips, and you'll have yourself an easy to detach wall of spare clips.

As always... the low quality pictures...

And now, even LOWER quality videos

[url=]Explaining some neat features of the gun
- This video is dark because we were filming it after the Sun was setting.

Being silly

EDIT: Adding this new video of the F.A.S.G

Hope you've enjoyed em, if you are curious, the range for a single shot is about 50ft at around 10 degrees, and for the whole clip... it's anywhere from 25-40ft (It decreases a lot since the motors are being slow downed by each dart it's trying to squeeze off). Although the 2nd video doesn't seem to show the gun firing very accurately, that's my fault for making inaccurate stefans. When using stock darts, the spread is very small.

Thanks for reading ^^)
« Last Edit: August 29, 2007, 11:10:56 pm by b00m13 » Report Spam   Logged

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« Reply #1 on: August 30, 2007, 09:50:58 am »

I don't think I have the skills to ever perform this....

But still its pretty freaking sweet! Great content, you get some points and a cookie! grin
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General Cole
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« Reply #2 on: August 31, 2007, 08:59:48 pm »

I WANT ONE!  And I can strap it to a crossbow!
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