minipump v4.1 mini (redundant?)

by **clide** » Mon Apr 11, 2005 5:44 pm

I built this one not long after the first v4.1. The design is the same as v4.1 in my previous thread, but scaled down a bit for a more compact and less powerful design. It is 3" shorter (4.25" long) and shoots around 100 fps. The main thing I like about this version is it can be pumped between your hands. The previous version could not(not by me anyway). Its quite comfortable to hold because the sleeve fits perfectly with the width of my hand. Anyway, here are the pics.
<a href="http://gbcannon.com/pics/minipump/v4.1/mini/size.jpg">Size comparison to a couple things while loaded</a>
<a href="http://gbcannon.com/pics/minipump/v4.1/mini/loaded.jpg">loaded</a>
<a href="http://gbcannon.com/pics/minipump/v4.1/mini/fired.jpg">fired</a>
<a href="http://gbcannon.com/pics/minipump/v4.1/mini/extended.jpg">extended</a>

Its been holding pressure wonderfully. I've left it charged for over a day several times and it still fires very strong every time.
Other than the occational botched pump, due mostly to slightly too much rubber being taken off the piston o-ring, I haven't had any troubles with it.

Edit: http://localhost/forums/viewtopic.php?t=8824 previous thread explains how it works and has pics of the inside...Looks the same on this version.

by **barillel** » Mon Apr 11, 2005 7:00 pm

Really nice gun... This is probably the most impressive design I have seen in the last year. I love compact fully-custom guns.

by **BillyBobJoe** » Mon Apr 11, 2005 7:04 pm

Ahhhh, double post!

Awesome Clide, you never cease to impress me (and others). I'm assuming it has the same barrel size (ID)? How much do you think this one costed you?

by **theexp** » Mon Apr 11, 2005 8:18 pm

SWEET, can you post a little animation or something, or is it the same principle?

**Sponsored**

by **spudman029** » Mon Apr 11, 2005 8:35 pm

I dont really understand how the whole thing works. Im guessing that when you pull the front part back, it pushes the piston forward, causeing the ammo to shoot out?

by **clide** » Mon Apr 11, 2005 9:49 pm

Yeah same barrel size (about .28" ID). These guns are extremely cheap as far as materials go. Just running through the costs in my head I got less than $5 with high estimates for everything. The main thing is they take quite a bit of time to make. I am getting better though. I think I was able to make this one in about 5 hours. 6 hours for the previous and probably well over 8 for the first.

<embed src="http://gbcannon.com/flash/minipumpv4.swf" quality="high" bgcolor="#ffffff" width="550" height="200" name="minipumpv4" align="middle" allowScriptAccess="sameDomain" type="application/x-shockwave-flash">
There is a flash to hopefully help you visualize how it works. Same principal as the last, so explainations of each step can be seen in the previous thread. All the forces actually firing the gun come from the gun's internal forces. The user creates the pressure and releases the pump from its locked position.

by **neue ziel** » Mon Apr 11, 2005 10:53 pm

so you wouldnt happen to have any of these for sale would you?

by **syco kilaa** » Mon Apr 11, 2005 10:57 pm

wow, I get it, or I think I do, so when you extend it, it alows air to come into the large chamber, then when you close it a piece of rubber blocks off the barrel, thus the air is pressurized, after it is "closed" the air equalizes between the front and the back of the rubber thing, so when you fire it, the whole barrel moves forwards allowing the air pressure behind the rubber diaphragm to drop, thus it is sucked backwards and the compresed air infront of it is directed into the barrel.

by **clide** » Tue Apr 12, 2005 3:09 pm

Looks like you got the right idea syco. Another way of looking at it that may help some people is that it is just a normal coaxial piston valve. When it is in its extended state it has a relatively huge pilot volume. When you push it in, this volume is decreased, creating pressure in the pilot chamber, which then leaks into the main chamber through a tiny leak hole in the piston. When it is released from the locked position the chamber, piston, and barrel all move forward (caused by pressure in the pilot area), leaving behind only the rear pilot wall. Which rapidly decreases the pressure in the pilot area, and the gun then fires like a normal piston valve.

neue: I don't have any made up that I can sell, but I would be willing to make them on request. If you are intrested you can shoot me an email to the address in my profile and we can discuss it.

by **ryanpowell167** » Tue Apr 12, 2005 10:00 pm

So...how much for this one. I made one like the other one but i lack a piston and the barrel has to be epoxied in....Im lazy. These things are so cool. It would be fun to just shoot someone in the ass and turn around and act like nothing has happened.