SpudFiles

So, as im still fairly new to the forums and have been commenting on things... I guess its time to build a cannon.

This design has been in the back of my head since I started lurking here, consuming every scrap of information available (Jesus... theres more than I will ever need...). From all that I have gathered here, I assume it isn't going to be super powerful or anything, but im okay with that. I know there are many changes that would up its efficiency, but for my first build I am more concerned with achieving a working launcher.

Few goals include-
-Artistic; parts and design must be visually pleasing.
-Self-contained; all parts must be mounted to gun... barrel, tank, pump, everything but ammo.
-Comfortable to operate; basically feel/shoot like a normal rifle.
-Semi-accurate/powerful; able to hit a coke can @20yards 8 out of 10 shots.

All parts used are listed on the Parts Layout Diagram pic. The design uses a blowgun barrel, and standard blowgun ammo (see link). Operating pressure will be 100-150psi. Dont know my barrel:chamber ratio yet, but this is just the first post. I figure I have about a week untill I have a working launcher... then maybe 2 weeks after that to finish all the "art" work on her. (LOTS of hand cut / etched brass plate. maybe some woodcarving)

These darts specifically... but any blowgun dart would work.
http://www.dellsmart.com/index.php?_a=viewCat&catId=16

Now, a few pics

EDIT- disregard the date stamp on the last pic... the year is off... new camera

Give me the facts and I'll give you the law?

You did go a bit overboard with the fittings, but if you're going for aesthetics as well I suppose it's justified. I should work nicely.

Why are there 2 check valves on your pump assembly? You only need one, closest to the cylinder assembly. It's also going to need considerable force to pump, at just 100 psi you'll need to put almost 45 lbs on the plunger. It would have been better to have a longer pump of say 1/2" diameter, at 100 psi force needed goes down to just under 20 lbs.

Also, shame about the hoses and clamps, they won't go well with the "steampunk" effect - I would have used copper tubing and ferrules, would set it off nicely against the brass.

If you can get up to reasonable pressure in the 100-200 psi range, your accuracy targets are more than achievable with a set of decent sights.

That looks great! I'm looking forward to seeing it completed. Good first launcher idea.

Zoltar9879 wrote:Good first launcher idea.

... though with some consultation before buying the parts I think it could have been further optimised in terms of performance.

that stock looks bloody awesome, looking forward for this one. i read your lay out and if your going with 3/4 inch pipe for the chamber you wont need two of them and if possible you should go with copper pipe in place of hose just in case you step up the pressure.

Thanks for the replies!

yeah... the fittings are a bit much however, as previously stated, im really only looking for something that works rite now. Anything else (power/accuracy) is just icing on the cake. As a matter of fact... im currently sitting at work designing my second build lol. I think ill post the design well before I buy parts this time tho... would be nice to have some confirmation of expected performance before the $ investment.

@ JSR- the two check valves work similar to a re-breather on a diving setup. On normal hand pumps there is only one o-ring... which is floating... and seals on the push... then allows air back into the chamber on the pull because is doesn't seal on the pull. My design doesn't use o-rings at all but rather washers cut from a sheet of gasket rubber. This means that the pump is constantly sealed (push AND pull), and therefore needs a way to let air back into the chamber. This may or may not be optimal (no background in this stuff... designing on the fly here) but I figured that it would be easier to build a high psi pump if there were more than one seal on the plunger (more seal=less chance of air slipping past plunger @ higher psi)... or at least thats my reasoning behind the design. I AM however, interested in your comments on smaller diameter/longer pump designs being easier to pump to higher psi... are there any threads on pump design theory?? (as a P.S. I would like to thank you for your post on a previous thread concerning handmade stocks... those artists were amazing... im always looking for inspiration.)

@zoltar9879- thank you thank you I fully intend on keeping this thread current with pics/info as I progress on the launcher. Keep your eyes on it as it will be updated often.

Also... any thoughts on my design concerning what kind of performance I should reasonably expect?? Such as... how many fps my projectile should be expected to fly...Max range... general stuff, im hoping that im not the only one to have combined this air-chamber size, with this barrel size and @ this psi.

have you got GGDT. plug in your numbers and it will tell you a pretty accurate estimation of the power of you gun.

Oh wow... nice program... hate to say that I dont have all the information required tho there is a lot of unknown with the projectile and the qev... guess ill just have to wait till the qev arrives in the mail and take it apart. TY for the link

ThornsofTime wrote:the two check valves work similar to a re-breather on a diving setup.

I get it now, I had misread the diagram - yes, it makes sense now one thing you should be concerned with is the volume between the end of the piston travel and the check valve to the chamber - this is dead space which is never compressed, and therefore will limit the maximum pressure you can achieve.

I AM however, interested in your comments on smaller diameter/longer pump designs being easier to pump to higher psi... are there any threads on pump design theory?

Remember that pumping effort is directly proportional to the area of the pump head, which grows exponentially with diameter - make the pump body twice as wide, and it will be 4 times as difficult to pump. Conversely, half the diameter and pumping effort is 4 times less, although of course to achieve the same pressure the number of pumps required increases.

I can do worse than point you to this excellent tutorial by Gippeto. There is nothing exceptionally difficult about floating o-rings

Here's another example to inspire you.

any thoughts on my design concerning what kind of performance I should reasonably expect?? Such as... how many fps my projectile should be expected to fly...Max range... general stuff, im hoping that im not the only one to have combined this air-chamber size, with this barrel size and @ this psi.

This sort of QEV launcher really shines with higher pressures (300-600 psi) but I have a feeling that with your current pump setup you will find it hard to go past 50 psi and performance might be a little disappointing.

Buy a floor bike pump and a screw in schrader valve. That would be your best bet IMO because you would save a lot of time on making the pump, And you would be guaranteed to be able to get at least 200PSI with a normal floor pump.

For less bulky air lines you could try paintball macroline. It's what I use. But seeing how you've already bought the stuff... Your attitude is a good one, you just want to get something done then improve it... I dig that.

Ok... Having read the recommendations and comments of others, I decided that it made no sense to build something I wouldn't be happy with.

I spent a few hours re-thinking the design and have a few questions.
A) do you think my design would work with one pressure tank?? (instead of two)
B) Given the changes, could this launcher be safe to operate up to 200-300PSI??

Changes
A) Moved to a 1 tank design, replacing second tank with a hand pump.
B) ALL hoses and clamps have been ditched for metal tubing.
C) Redesigned hand pump... single one-way valve... plunger now works with a single floating O-ring.

@JSR- took me a while... but I eventually agreed with you that the hoses and clamps had to go. Thanks again for the pump info... and yes your Latin isn't too shabby (or your google translator )

I submit to you.... PLAN B!!!!!

@Lozz08- The idea of a self-contained gun (aka not having to lug around a pump) is VERY important to me. Im not closed to the idea for future builds, but for this one... I want to be able to take it out to the field with friends and plink. And yeah... caught red-handed... the design before my first post (was really just doodles on paper) used paintball air accessories

Yeah... TOTALLY just realized that I didn't have an avatar... FIXED

Looking good

ThornsofTime wrote:A) do you think my design would work with one pressure tank?? (instead of two)

Definitely, if you can get to 200-300 psi, and it will be a hell of a lot quieter too

B) Given the changes, could this launcher be safe to operate up to 200-300PSI?

Yep

and yes your Latin isn't too shabby (or your google translator )

It's a known enough phrase in English, but yes, I took Latin as a secondary credit at university

The idea of a self-contained gun (aka not having to lug around a pump) is VERY important to me.

A regulated paintball bottle would give you many shots before it would need to be refilled, it might also be an option if you had a convenient way of filling it.

If you want to keep the on-board pump byt reach higher pressures/reduce pumping effort, adding a lever might be a good idea as oncommercial multi-pump rifles.

You'll need to mod th QEV to fill chamberside, but you've got a great design there

Looks sexy! You're off to a good start there; Can't wait to see it all put together!