Electronicaly triggered BBMG

[evilvet]

Hi all,

Just for fun I am using some old parts from the workshop to build a new toy. The idea is to use a gravity fed hopper for 0.177" BB into a breech block. At the base of the block on the vertical axis I have a spring loaded 12v coil to act as a plunger and prevent BB's falling from the hopper into the breech.

On the horizontal axis a 5.56mm air tube is fed from a 100psi shop compressor, leading to a 600mm barrel of 7/32" brass tubing.

Basicaly you have a horizontal air stream at 100psi in a 5mm orifice. BB's are gravity fed from above, dropping into the air stream when the coil plunger retracts. The end result is a stream of BB's at a fairly hefty rate of fire.

Prototype of a three round burst penetrates 3mm plywood at 20 feet.

Any thoughts appreciated.

[jackssmirkingrevenge]

Sounds interesting, photos/videos of it in action? Something like this from what I gathered from your description?

[evilvet]

All due homage to Yoda, he replies with graphics that are perfect. I am a long time lurker and admirer of the master, and yes, you got it right first time.

I have made the prototype from HDPE and not yet fitted the plunger; just doing a hand loaded 3 round feed into the top of the block. I will post some photo's / video tomorrow as it stands.

My local plastic fabrication man, a dude I higly recomend at plasticcenter.com.au is making me a breech block from acrylic so I can watch and film the solenoid in action.

As to the timing circuit, I am intending to use a 555 chip to pulse a relay, giving "dial and fire" from 3 round burst to full auto rock and roll.

Stay tuned.

[POLAND_SPUD]

555 chip

get a timer relay... that's a thingy that does what you want to achieve... and since it is already a relay there is no need to add another one

[django]

Wow this sounds fantastic!!, great to have another Aussie on here too theres only a few of us, once I understand construction of this a bit better and get more info I want to have a go at making this too.......

[jackssmirkingrevenge]

All due homage to Yoda, he replies with graphics that are perfect. I am a long time lurker and admirer of the master, and yes, you got it right first time.

I try glad to be of inspiration

Since you have the facility of a solenoid and preceisely manufactured parts, might I suggest you refine the design a bit more? As air goes into the hopper, some pressure is being lost due to expansion. Why not consider some sort of reciprocating bolt that blocks off the hopper for every shot?



This is as far as I got with something similar but in the end I wanted an air-only device without resorting to electric assistance.

[mark.f]

and since it is already a relay there is no need to add another one

555's are not good for a lot of current (at least the ones I buy around here). You're usually good driving a MOSFET or another NPN power transistor (2N3055) that switches current to your load. Relays, being an inductive load, also have a chance of frying the delicate little chip.




Anyways, sound like a neat little gun you've got there, evilvet, though I wonder why you didn't just use a solenoid valve to control the air supply?

[POLAND_SPUD]

@mark.f
uhmm I don't get it... that's why I suggested using a time relay instead of a 555 timer

in case you don't know what I am talking about http://www.allaboutcircuits.com/vol_4/chpt_5/3.html

[mark.f]

Ah, my bad. Disregard that. I thought you were talking about a 555 chip.

[POLAND_SPUD]

yeah no problem...

I just want to point out that for most people these things are a better alternative to 555timers

they are off-the-shelf parts, can be bought cheap, they work well, handle high currents well, etc.

sure, if you are an electronically inclined guy you can build your own 555timer that is smaller, cheaper and lighter than time delay relays but this is by far the simplest choice...

pretty much in the same way as QEVs are almost ideal piston valves... sure you can build your own but for 90% of cases the QEV is the answer

[evilvet]

Anyways, sound like a neat little gun you've got there, evilvet, though I wonder why you didn't just use a solenoid valve to control the air supply?


Sorry, I did not make that clear. There are two solenoids involved here, both fired from the same DPST switch. The first one controls the air supply, the second drives the plunger. The idea is such that even if the plunger fails or jams in the open position due to some sort of misfire, the air supply solenoid will close once I release the trigger so no nasty surprises. The plunger solenoid is there so that the hopper cannot just gravity feed and have BB's roll out the barrel when the air is off.I also added a closure to the hopper to deal with the "blowback" problem and loss of pressure. First test shots resulted in a fountain of BB's up from the hopper as barrel pressure built up

Photos later today

[evilvet]

Afternoon all

Video at http://www.vimeo.com/11481048 will give an idea of the concept. Not much to see but may be of interest.

Cheers

[Gun Freak]

Looks good but I think you should take away the hose between the solenoid valve and mag cuz it only makes dead space.

And where I live its 10 pm. lol

[jackssmirkingrevenge]

Ack, can't see the vid from work (because it's a bit hard to ask the IT department to upgrade your browser when the only reason we can come up with is "we cannot watch youtube anymore...") but I'll check it out at home.

[evilvet]

Just uploading a new video on using stepper motors to control a 2-axis turret. I had this in the back of my mind for a while since starting on a home built CNC router.

The pan axis is easy, I converted an old belt drive turntable to stepper control. The altitude axis is opening a couple of options, one is to use the traverse workings from a CD-ROM drive to convert the radial stepper motion to linear movement on the tilt axis. Another is to use a continuous loop cable drive with spring tension compensators to give a deflection of +/- 30 degrees from horizontal.

We will see what the next few days bring.

What I will have is a 30-50 RPS BBMG with red dot laser targeting, web cam POV imaging, USB laptop control of a 2-axis turret and all built for under $300.

Now I can combine BBMG, stepper control. basic mechanics and hiding in the workshop for hours all in one fruitful pursuit. Smells like teen spirit to me..........

Video soon