minipump v4 (minipump pocket)

Just build a cannon and want to show it off? Post it in here.

Postby clide » Wed Mar 16, 2005 4:56 pm

Not an upgrade, just a new design.

Its basically just a coaxial gun that uses the gun itself for a pumping mechanism and uses an expanding pilot volume rather than an exhaust valve. The entire thing is 7" long when closed completely and the outermost pipe is 1" nominal. Here are some pics:

o Starts out in a <a href="">slightly extended state</a>
o The pump (gun) is pulled out as the operating sleeve is pulled back. Once the extended groove reaches the BBs the operating sleeve is able to slide back, locking the gun in its <a href="">extended state</a>
o The muzzle is placed on the ground and both the operating sleeve and pump body are pushed downwards. Once the loaded groove reaches the BBs the operating sleeve slides forward locking the pump in its <a href="">loaded position</a>
o Projectile is loaded and gun is <a href="">ready to fire</a>
o Pump body is pushed forward with the thumb and the <a href="">firing slot</a> on the operating rod is moved over the BBs.
o Pump body then moves froward from the pressure behind it, the pressure drops because the volume is increased, and the piston actuates, the pump body ends up back in its <a href="">slightly extended state</a>, ready for the process to repeat.

Some pictures of the inside:
<a href="">opened</a>
<a href="">opened front</a>
<a href="">opened rear</a>
<a href="">internals close up</a>
<a href="">view of chamber</a> Only 1" long (less now) From the outside, the chamber ends .5" before the seem that can be seen on the pump in other pictures.

I had some issues at first. The o-ring groove was too deep and the pump was getting stuck in it's loaded position because it wasn't holding pressure. To extend the pump agian I stuck a wire with an L on the end down the barrel and hooked it around the end and tugged. It worked, but the barrel is just thin aluminum and it bent the end of the barrel where the piston needs to seal. So rather than redoing the entire pump I put it on the lathe and cut off the part below the seam, and took .1" off the barrel. I then remade the part below the seam and used a .1" longer piston. And to prevent the bending of the barrel anymore I <a href="">tapped a hole in the front of the pump</a>.

Seems to be working fine now, the piston still doesn't like sealing with the barrel for some reason, but I put an o-ring around it and cut it up some so it wasn't a perfect seal and that helped some.

Chrony shows speeds around 160 fps with a Tic-Tac, but GGDT was predicting 230ish, so my only guess is that this method of actuating the valve slows down the opening speed of the piston by quite a bit.
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Postby ryanpowell167 » Wed Mar 16, 2005 5:10 pm

That is awesome. That would be cool to have one of those and shoot bbs during class to have wars or something. How did you think of that? I would have never thought of anything like it. Great job. tic tacs could be like inconspicuous ammo. The teacher catches you and all she takes it the tic-tacs. Say the gun is a pen[:p]. You wouldnt happen to have one of those up for sell would you?
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Postby clide » Wed Mar 16, 2005 5:43 pm

I can't quite remember how I thought of this one...usually I remember my thought path, but I'm not quite sure in this case. All I can remember is that I was in the shower. Its probably too big to be considered a pen, but it could probably be scaled down a bit if you were shooting something like BBs.

And its probably too powerful to just kid around with, it's not as powerful as my other verions, but it can still shatter a Tic-Tac on a hard surface. I was going to shoot my arm, but I wimped out. Last time I did that with something I thought wasn't powerful it left quite a welt.

A nice little feature of this thing is that it gives a pretty solid POP without anything in the barrel, but is pretty quiet when shooting a Tic-Tac. I think the barrel is just a little longer than optimum according to GGDT. I may try to get a video of it later if anyone is interested.

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">You wouldnt happen to have one of those up for sell would you?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Depends, how much are you willing to pay [:p] I could use the money if its a decent price. Took me an entire day minus the screw up to make the first one. Another could go a little quicker.
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Postby pyroben » Wed Mar 16, 2005 6:54 pm

could you make up a set of plans?
what kind of tools do you need?
Could you make a set of materials?
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Postby theexp » Wed Mar 16, 2005 8:21 pm

I was wondering the exact same things as Ben
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Postby ryanpowell167 » Wed Mar 16, 2005 8:39 pm

How much you want for one. I could probobly have some cash in the mail, in the next week or so :)
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Postby syco kilaa » Wed Mar 16, 2005 9:05 pm

wow, thats all I can say, I really like the fact that its so small. could you possible send me some plans? plz?
syco kilaa
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Postby ryanpowell167 » Wed Mar 16, 2005 10:05 pm

I only wanna buy one because i dont think i could build one with plans [:p]. How much pressure do you think you're generation in that? Thats every impressive. You have quite an imagination. It kind of makes me qestion you, that you thought of this "pump" gun in the shower.....

EDIT i wanna see a video of how you pump it and stuff, i was a little confused on that.
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Postby clide » Wed Mar 16, 2005 10:34 pm

Sorry no plans. Exact dimentions could vary based on the pvc you get your hands on, plus all the parts can be seen in the pictures, and I'm sure all of the pieces could me made by different dimentions. Perhaps if this were a final version I would consider it, but there are so many things that could be improved upon that its not even worth it in my eyes. I already have several things I would do different if I build another, and I have only been using it for a day.

But I will give a part list because I can see how that could help.
1/2" sch40 pvc for the pump
3/4" sch40 pvc for the pump body
1" sch40 and sdr21 for the operating sleeve and sleeve stop
4 .177 cal BBs for stops
some pvc rod for the end plug for the pump body, piston, and barrel support/chamber plug
some rubber for piston face
o-ring for pump seal.
set screw for piston stop (I use 8-32)
Barrel (I use 5/16" OD tubing that I found at my Ace hardware)

Tools needed:
tap (for the piston stop screw)

I've made an Excel spreadsheet to give info on pressure created with a certain size pump or chamber/pilot, or pump size needed to get a certain pressure for a certain chamber/pilot, or the chamber/pilot size needed for a certain pressure with a given pump size. It is predicting 150ish psi for this gun. I haven't verfied that yet, but it feels about right for the ammount of force needed. If anyone is seriously considering building one I can post the spreadsheet if ya want.

I'm not really sure how much to charge for the thing. As you can see above the cost of materials isn't much at all, so the cost would be based on labor. Just offhand I would say $50, but only building one its hard to pin down exactly how much work I put into it.

Oh and almost forgot <a href="">here is a video</a> Divx is needed to play it.
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Postby ryanpowell167 » Wed Mar 16, 2005 11:36 pm

Ok, tons of questions. On the body, i see some rings inside the 1". Im guessing that is to keep the 3/4 tight in there? What are those? Did you bore them with your lathe? How did you hold the barrel securely in the pvc? Do the bbs go in the holes in the 3/4" part of the body, and when you pull the barrel assembly out they get lodged in the firing slot? Whats inside the 1/2" pvc? rod lathed down to fit inside? Whats the groove cut above the oring in the 1/2" part? Whats the groove cut in the 1/2" part at the end of the barrel assembly?How did you cut a groove for the bbs on the inside of the 1"? Could it be done without a lathe? Could you have used en endcap on the 1" or do the multiple parts serve a perpose? Whats the length of the 1" body, 3/4" body and 1/2" body?On the 1" body it looks like you could have used 1" sch 40 on all of it because it fits the 3/4" perfect doesnt it? Couldnt you make the chamber larger by reduceign the length of the plug that holds the barrel, or would this cause too low a drop in psi?When you pull the barrel assembly out to cock it, doesnt it creat a vaccuum behind the oring or does it have a thing to release it? Im sorry for asking so many questions but i realllllly want one, and i dont have 50 bucks :(

I think i get it!!! Maybe, i can build one by improvising....probably wont be as good as yours.Maybe i will think of something.

Plans would be really cool too!!
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