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10X Hybrid golfball launcher

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: mobile chernobyl » Thu Jun 17, 2010 12:06 pm

No prob, this pdf is gold for this sub forum. Unfortunately (and expectedly) they do not list the ratios of the compounds,

Perhaps the most interesting part in there is the discussion of the diluent. they are using helium, nitrogen or just an over abundance of fuel to avoid DDT!

For having a preignition chamber pressure of 20KPSI.... and no DDT - I think a mandatory thorough read-through is in order!
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Unread postAuthor: DYI » Thu Jun 17, 2010 5:34 pm

@mobile chernobyl: Good job on finding that PDF. I searched about two years ago for information on the same project, to no avail. What surprised me on reading through the file was how little of it was new to me.

Most of us who found Utron's CLGG project two or three years ago guessed that it operated in the range of 1000X - 2000X (which, with the fueling chemistry shown in the PDF, appears to be right in the ballpark). Some of us were convinced of a liquid propellant, while others guessed (correctly) at the use of what was essentially HyGaC20's configuration, with less buffer gas and pressure scaled up by a factor of ten. We all found it likely that the burst disk was connected to the projectile, although I don't believe the actual design (which is quite ingenious, if useless to most of us) was thought of.

What was most obvious during my reading of the first ten pages was that they had implemented every feature me and Larda had discussed to bring HyGaC20 up to 400X and 2km/s capability (hydrogen as a buffer gas in H2/O2 mixes being particularly notable). Based on what I know from reading the PDF, the performance of the 45mm gun somewhat exceeds what I would expect for that mix number and chemistry, and the achievement of 25% efficiency at such high speeds is simply amazing.

Great find mobile, and good luck with your hybrid.
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Unread postAuthor: mobile chernobyl » Fri Jun 18, 2010 12:21 am

It's amazing what you can find if you know how to search :wink: jk... Your a pretty clever lad lol

That was publicly available circa 2006-07 I believe - So you should have had no problem finding it using simple keywords like "ultron combustion light gas gun".... That's all I used lol.

That said - I still suggest saving the PDF to a reliable storage place.

More useful to me almost is the list of resources and the biblio. on page 25 - give it a look cause they start to go more in depth in discussion of propellant chemistry.

I had a similar feeling of "hmmm that's what I was thinking! if only I had a DOD grant... and a professional machine shop... and a better CFD program than what I currently use lol" - the CFD done by CFX is pretty amazing - not sure if you've done any advanced fluid dynamics problems by hand yet in your schooling's, but they are a bear and that's only in the 2D realm...

I wonder why Mr. Hall isnt working with these guys? or is he.... :idea: lol

Sadly after finding this... yea... this current gun just isn't big enough. A 500X is going to be made in the future, gimme a year or two though. :D
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Unread postAuthor: Gun Freak » Sat Jun 19, 2010 8:58 pm

mobile chernobyl wrote:Sadly after finding this... yea... this current gun just isn't big enough. A 500X is going to be made in the future, gimme a year or two though. :D


Let's leave that up to larda :D
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Unread postAuthor: mobile chernobyl » Mon Jun 21, 2010 1:31 am

Lol we'll see... can't let Larda have all the fun now can we...


Here's the latest HGDT predictions to an accurate AS-BUILT model of the gun (some dimensions changed due to a bad weld that needed to be cut out and re-worked)

One major benefit of parametric modeling programs is that - they can calculate volume of 3d Solids for you! So as long as you have an accurate model of what you've built and know all your materials spec's (in my case wall thickness's) then you can produce an accurate measurement.

My volume came almost exactly to 130 cu in... without trying lol.

The meter tube is pictured below that. It will consist of 7" of barrel material essentially. The volume of it is about 16 cu in.

To anyone whos used it - Can I trust these HGDT numbers for constructing the metering tube? I assume Mr. Hall has done a great job on this, but I just want to hear it from someone first hand that build a meter tube using the given parameters. All the math checks out so I guess I shouldnt really worry but someone's positive first hand experience will probably convince me to make it faster :D lol
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Unread postAuthor: Technician1002 » Mon Jun 21, 2010 3:48 am

For minor variance not caught in the measurements, the model is a good start. Bracketing your pressure much like a photographer will bracket the F-Stop to get the perfect exposure, you can experiment to dial in the correct pressure. Errors arise in the tube between the meter and chamber and it's contents, temperature changes with pressure changes, pressure gauge callibration, ball valve volume, etc.

Use the math for a baseline to tweak from. Try pressure brackets of +/- 2%, 5%, etc and find the direction with the most improvement.
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Unread postAuthor: mobile chernobyl » Tue Jun 22, 2010 12:12 am

Some more Renders for anyone interested. :wink:
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Free and easy burst disc for 1.5" unions! Almost...

Unread postAuthor: mobile chernobyl » Wed Jun 23, 2010 5:54 pm

That's right... found a nice free burst disc for my union today. I haven't analytically calculated the burst pressure yet, but the material thickness is a pretty uniform .012". The alloy used is supposedly 3104-H19.

I tested it and it holds pressure great!

Problem is - my unions are on backwards for this to work properly - for now. The cap inverts around 120psi and the seal is broken - most likely because of a forced alteration from the material stretching.

So almost! The catch is (and i'll find out after I run some FEA on a similar model) I dont think it would have worked that great for a 10X rupture disc anyways.

So it looks like its back to ye olde drawing board for a little while...

In the mean time I found a nice little bit of math here:
http://www.ansys.com/events/proceedings ... RS/227.pdf

Based on that, I can use the formula:

Burst Pressure = (UTS * Td)/(k * d)

Where:
UTS = ultimate tensile strength
Td = Thickness of disc
k = material's k factor (I figured out how to find this below)
d = diameter of disc

with the known information:

Just desiring to get results at all, I will use .3 in a simple calculation (C122's k factor), The rest of alloy 110's properties I'll use are:

UTS = 31.9KSI
Td = .015"
d = 2"

PB = 797.5psi.

Thats Ideal!

Now just how to determine c11000's k factor since that is the most common available alloy for copper sheeting.

::EDIT::

I found a paper referencing this unique k factor (k factor is just a number, usually unique to the process your trying to calculate)

http://www.platinummetalsreview.com/pdf ... 42-046.pdf

k = (D*P)/T

where:

D = diameter of orifice
P = pressure at burst
T = disc thickness

Of course this is still an experimental way to find k...

-However you can determine K from the chart given on page 3 of the 2nd .PDF I posted.

-----------------------------------------

Good news!!! I managed to find another Concentric reducer and Socket Weld union in our junk parts, so looks like I have been given a second chance to get this right!

I plan on trying to use the soda can bottoms if possible, I've run the same calculation as above on them and have gotten promising results.


Soda can alloy = 3104-H19 or 3004-H19 aluminum, Specs to those materials are:

Ult Tensile Strength -
3104 -> 42100PSI
3004 -> 42800PSI


Using:
Burst Pressure = (UTS * Td)/(k * d)

I've determined the following:

UTS -> 42KPSI (low side)
Td -> .012"
d -> 2"
k -> .3**

**determined through the charts slope

Bp = (42000 * .012)/(.3 * 2)

Bp = 840PSI

That's perfect... if true!

:D

------------------------------------------

Another mini update - Calculated aluminum foil with this formula - it checks out!

Aluminum foils UTS is appx 311MPa which comes to about 45KSI

Using a micrometer, aluminum foil measures to be around .0001" (calibrated the micrometer with standard shims down to .001")

Using the same perimeters (sticking with k value of .3)

Bp = 7.5PSI.

A little bit more confidence inspiring!

:o
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Unread postAuthor: mobile chernobyl » Sat Jun 26, 2010 3:57 am

Well, it was bound to happen.

8)

Stand has recoil absorption built in now. I couldnt stand looking at Larda's and thinking about how crude my design was lol.

I got rid of the pipe clamp support system, for 2 main reasons:
1 - I didnt want to have to loosen the barrel end every time I wanted to load ammo - I wanted the barrel supported, yet still "floating". This was not possible until I was forced to redo my union for burst disc placement optimization. Now with the chamber been the threaded end of the union - it needs to resist rotation - this is taken care of with the dual rails supporting it - yet allowing it to slide.
2 - I'm not 100% sure they would have enough friction acting upon the surface of the chamber (remember, it's near polished stainless now) and if they didnt, I didnt want to be behind the gun at all when it was firing - trust me that's not a cool feeling to have lol. :roll:

The 3 front barrel supports are 3" x 1" UHMW bar stock - they will allow barrel support, yet sliding of the barrel to breech load stuff.

The shock absorber will be something from a car - I'm not familar with car stuff so much as bike stuff, so I'll hafta look into this, but the eye-to-eye measurement is similar to what a lot of Honda's use so I'm not worrying about it not fitting in the future when I go to make it. I need to figure out the damper's actual "spring constant" since they are usually always nitrogen charged. The shock will be driven in a 1:1 ratio too - so I need to make sure it's not being over driven as per original application's specs.

The gun will slide on two 1/2" stainless rails, giving about 6-7" of travel dependent on the shock of course. The gun will have two tubes welded to the sides of it to accommodate this (probably the last step I will do in making the frame since this step is absolutely crucial in lining up correctly to avoid unnecessary binding.

Jury's still out if I should go full on howitzer and put wheels in the front, or keep it tripod like my previous renders.
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Unread postAuthor: Crna Legija » Sat Jun 26, 2010 4:19 am

Looking good, but i think that you should get more travel on the recoil absorption system 6 inch isn't much (that's what she said).If you only shoot golfball it'll be alright, but put a half kg lead slug in there and i think you might want more
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Unread postAuthor: SpudFarm » Sat Jun 26, 2010 8:45 am

-_- wrote: but put a half kg lead slug in there and i think you might want more


The recoil of those cannons really aren't as brutal as you would think.
If you saw how I mounted my cannon and consider that it moved about 3mm backwards on a shot with a 850g lead slug.

I think your system is awesome! There is so much beutiful stuff on this forum at the moment. I really regret that I made my hybrid as big as I did..
I do have a chamber that I can use to make a smaller one though. Something like what you are building fired from the shoulder would be quite an experience!

Keep up this Mobile. Looking great!
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Unread postAuthor: mobile chernobyl » Sat Jun 26, 2010 2:23 pm

And to copy Larda even more... :wink:

Using simple physics, I can calculate the maximum recoil force of the gun (appx 25lbs in finished form) firing a 1000gr (thinking the heaviest thing i will ever fire) at a 12X mix.... I get a recoil force of around 950ft/lbs.

Now i'll round that up to 1000ft/lbs and I'm going to need something to catch and damp all that recoil. Figuring thats going to be the most this gun will ever fire, I'd rather allow for smaller payloads to be absorbed as well. So im increasing the travel of the gun sled from 6" to 8" now. This will allow me to keep a lower spring constant to accommodate for smaller recoil forces as well.

Why? Well I still kinda wanna make this thing turret operated, by a human, not remotely for most shots (after 9 or 10X i would remove the human from the situation for safety).

so what I've done is found some 20" eye to eye gas springs, they have a 8.375" stroke. Their spring constant is 60lb/in.

so that gives me:

2 * 8.375 * 60 = 1000 ft lbs of resistance force.

Now figure that air as it compresses is not linear, so there is a factor of progressiveness there. I've seen anywhere from 25% and up, depending on a few variables. For one the gas inside the spring is pure nitrogen. Another thing is starting and ending volume in the spring itself - this is not published. However I do know that it is not linear, so I will be getting more than 1000ft lbs of recoil absorbing action at the extreme end.

Unfortunately (well not really) this only allows the gun to travel .25" for a golf ball at 15X mapp. That only exerts a 30lb recoil force, so its not really needed then.
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Unread postAuthor: Ragnarok » Sat Jun 26, 2010 4:15 pm

mobile chernobyl wrote:Using simple physics, I can calculate the maximum recoil force of the gun (appx 25lbs in finished form) firing a 1000gr (thinking the heaviest thing i will ever fire) at a 12X mix.... I get a recoil force of around 950ft/lbs.

Just a quick question... did you include the momentum of the gases in the equation? They can make quite a big difference.
(I'll also assume that the 25lbs is just the moving sled proportion, although it can be worth doing the calculation both ways)

so what I've done is found some 20" eye to eye gas springs, they have a 8.375" stroke. Their spring constant is 60lb/in.
so that gives me:2 * 8.375 * 60 = 1000 ft lbs of resistance force.

Ah. You've made a bit of a boo boo here.

a) The spring equation is kx<sup>2</sup>/2, not 2kx.
b) You've mixed your units. It's really important not to mix inch pounds and foot pounds.

The energy stored in a 8.375" spring with a 60 lb/in constant is 2104 inch pounds - which works out at 175 ft-lbs.
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Unread postAuthor: Ragnarok » Sun Jun 27, 2010 1:12 pm

For whatever reason, my last post here hasn't shown up on "recent posts", so because it's quite important that mobile chernobyl reads it (and reasonably soon), I'm afraid I'm going to have to bump this.
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Unread postAuthor: Technician1002 » Sun Jun 27, 2010 5:04 pm

Instead of working with Newtons, I worked from the force. For every action there is an equal but opposite reaction. From that I knew how much peak force to expect on the cannon. If the force is matched, a launch without recoil movement is possible. When it is unmatched, there is movement. When unmatched, using mass 1 : Mass 2 the relationship between the two masses can be found to find the maximum velocity the launcher will come back. If the velocity is low enough to safely catch, then I know it will come back into me, but with manageable speed to arrest the movement in a reasonable distance.

This was used to predict the Gatorade shot before launching a full one. We knew it would kick hard, but withing limits to contain it. We could have calculated the KE in the recoil if we desired, but didn't bother.

If unstrained, what is the maximum recoil velocity of the launcher? If restrained, what is the maximum recoil force on the launcher? Do you want behind it when it goes off?
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