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Kick'n'Blow

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Kick'n'Blow

Unread postAuthor: LeMaudit » Sun Apr 26, 2009 5:39 pm

Hi guys,

I have played a lot with GGDT, what a wonderful toy! :-)
I played enough to finally understand by varying parameters that the length of the gun I have in mind (being a single or 6-shooter) limit the possible velocity and the kinetic energy because there’s no time for acceleration. Unless going to crazy pressure levels!
With a 30 inch long gun, it would start to be enough, but that’s not my goal. I really would like to make a handgun, not a short rifle ;-)
Also, I plan to have relatively heavy arrows, because a good kinetic energy is what I would like, much better than a high velocity. I don’t plan to be accurate on long range; still I would like some powerful damage picture to show!

Anyway, while thinking about how to increase the velocity and kinetic energy on a short distance (and not doing a crossbow!), I figured that I could use a part of the energy store in a spring to give a good kick, when the compressed air start to blow.

Here’s a crude drawing (not to scale).

You can see the arrow is hollow, this gives me the opportunity to kick from the inside when the spring expand, and at the same time use the rapid air decompression to continue increasing the velocity while the tube is blow from the inside. Like in those nerf guns :-)
Maybe a bit tricky to adjust! It gives me also a way to have a very light arrow back but well sustained in the air, while having a heavy steel tip. This should improve accuracy on middle range.

Maybe I’m just rethinking the wheel here and the Kick’n’Blow is just a fancy name for old stuff. As this being attempted before? What do you think?
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Unread postAuthor: Sparkie » Sun Apr 26, 2009 6:04 pm

You are using the pin to force the projectile to start flying followed by the compressed air giving it force?
Sounds like it could work. Do you need to give it a kick? Just the compressed air would send it flying.
Also what is the hole in top of the chamber for?
looks like you would get the air for the spring area from your firing pin hole

Also how would you load the spring? I cannot see how it can be compressed. let alone having the power to pull it back if the spring is very powerful.
Still these are why we try these thing so we may learn


8) 8)
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Unread postAuthor: VH_man » Sun Apr 26, 2009 6:45 pm

Looks Very interesting. I think it will yield better performance if you leave out the cool spool-valve like mechanism, but then again nobody has ever tried this.

Interesting Idea though. If you make it work, Be sure to compare it to the normal no-valve type.
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Unread postAuthor: LeMaudit » Sun Apr 26, 2009 7:00 pm

Yes. I figured the length of the arrow itself is not enough to accelerate. The kick would hopefully give some additional kinetic/muzzle energy and acceleration from the start. Then the compressed air would provide additional acceleration. Of course I could be completely wrong :-) But that's the idea I had to compensate a very short barrel length for a handgun (6 inch or so)

The hole would be as an intake when the spring is compressed. The little black circles are O-rings, and it would create a vacuum in the chamber. The hole would provide positive pressure to the chamber at the end.

I would load the spring from the back. I just over-simplified the drawing with a pin there to lock in place and I didn't draw the loading mechanism I have in mind. But as you ask, it would be a longer rod after the pin that would be threaded. A simple nut rotated using a power drill should be enough to compress a short, yet very powerful spring (maybe the conical type with a shorter compression length). The thread would provide demultiplication force. Easy way to reload on the field, with one of those tiny but powerful cordless drill ;-)
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Unread postAuthor: Sparkie » Sun Apr 26, 2009 10:04 pm

Nice idea. Maybe you could make the dart so it is forced over a couple of o rings at the back. That way you could get the pressure build up until it "forces" the dart of the o rings for more kick.
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Unread postAuthor: Technician1002 » Sun Apr 26, 2009 11:16 pm

Sparkie wrote:Nice idea. Maybe you could make the dart so it is forced over a couple of o rings at the back. That way you could get the pressure build up until it "forces" the dart of the o rings for more kick.

I mostly worry about the diameter of the air piston in the drawing. If the ID of the dart is 1/2 the diameter of the air piston, the mechanical advantage (disadvantage) is based on area. It's a 4:1 reduction in area meaning a 4:1 reduction of spring force. If your spring pulls at 100 LBS the dart will only see a 25 LB push not counting any other losses.


There is also the "dead space" between the piston and projectile.

I have seen a version of this where the piston was inside the barrel inside the projectile to provide a mechanical advantage and used the air as an elastic collision between the spring pushed piston and projectile.

The kids book "Peter and the Wolf" shows one of these. The old pop guns that blew a cork out of the barrel worked this way.
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Unread postAuthor: LeMaudit » Mon Apr 27, 2009 7:55 am

Thanks for your comments. The drawing is really not to scale. The rough scale I wish I could make working would be I guess a 6 inch long barrel/arrow, 1/4" inside diameter, the internal pushing rod something like 1/8" or 3/16". This would make a dead space (the inside of the barrel) relatively smaller. I also guess the diameter of the chamber/spring would be ideally about 1". The length (including the spring maybe 3 or 4". But I need to do more math to be sure, and adjust to whatever spring I can find.

I am not sure I understand you numbers, sorry. Would you care to elaborate a bit? With my intended sizes perhaps?

I don't want to use the air as a cushion, but really as an additional force to propel the arrow. The kick would be just a start, to gain some momentum before the air start pushing. I figure I can save a length of a barrel that way. I've never see a pop gun working like that.

I was guessing compressed air will have a better efficiency than simply pushing an arrow with a rod. I was not able to find anywhere some numbers for spring expansion velocity. Only force. Anyone have some opinion on that?
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Unread postAuthor: inonickname » Mon Apr 27, 2009 8:31 am

Rather than using a mechanical spring you can use an air spring. All it would require is a floating o-ring to seal the air. Such mechanisms are used on high performance springer air guns- though usually with a gas like nitrogen.

Air springs allow easy and fast adjustment over tension etc.. The only obstacle you will have is airtighting the system. Not too difficult.

Mainly agree on the comments through here.
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Unread postAuthor: Big-E » Mon Apr 27, 2009 11:31 am

Actually, that's considered a catapult/pneumatic hybrid system. your typical red ryder bb gun works off the same principal; A pin connected to the piston kicks the bb forward initially, while the air compressed by the piston pushes it the rest of the way out the barrel. It definitely works in that regard.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 27, 2009 11:37 am

Realistically, I think that would punch the bolt straight through the head of your projectile. When it start moving, ideally the bolt head is already touching the projectile.

Personally I would use air only ;)

I would also advise against "spigot" type launchers where the projectile is wider than the barrel, they tend to limit performance.
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Unread postAuthor: covey12 » Mon Apr 27, 2009 1:30 pm

looks new to me, im sure someones tried it though, cant wait till you build it, if you do could you take some detailed photographs or videos maybe so others could learn how to construct one? i dont mean to sound pushy sorry
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Unread postAuthor: LeMaudit » Mon Apr 27, 2009 2:12 pm

your typical red ryder bb gun works off the same principal;


Really? I would not have though that, but my only experience is with a high-end Diana spring rifle, and I'm almost sure there is no pin that kick the diabolo pellet.

Realistically, I think that would punch the bolt straight through the head of your projectile. When it start moving, ideally the bolt head is already touching the projectile.


My point was to add kinetic energy to the arrow right when it start moving, as I don't have a length for enough acceleration. Air only would provide increasing acceleration, and my simulations using GGDT all shown that a longer barrel would be necessary to reach an interesting full speed/energy. I was trying to overcome this problem.

Personally I would use air only


My first idea was that, but again GGDT shown that I couldn't reach my goal with a short barrel (6 inches or so)

I would also advise against "spigot" type launchers where the projectile is wider than the barrel, they tend to limit performance.


Can you please elaborate on that? I would have thought initially that because of the relatively loose friction, only with a O-ring at the end, it would have being better energy efficient. And also would have keep the arrow from falling, which is a plus. But I would like to learn :-)

looks new to me, im sure someones tried it though, cant wait till you build it, if you do could you take some detailed photographs or videos maybe so others could learn how to construct one? i dont mean to sound pushy sorry


It will be my pleasure. On my web site usually I often describe the full machining process. like those:
http://www.nutsnbits.com/nutsnbits_00006d.htm
http://www.nutsnbits.com/nutsnbits_000079.htm
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Unread postAuthor: Big-E » Mon Apr 27, 2009 2:54 pm

Quote:

Really? I would not have though that, but my only experience is with a high-end Diana spring rifle, and I'm almost sure there is no pin that kick the diabolo pellet.


Yup, it's true. You can read all about how the lever action bb repeater's powerplant works at the link below. it's quite interesting.

http://www.pyramydair.com/blog/2007/02/bb-gun-powerplant-how-it-works.html
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Unread postAuthor: LeMaudit » Mon Apr 27, 2009 2:58 pm

Geez, can't believe it!! I do have reinvented the wheel :-D I'm kinda proud of it though ;-) Thanks for the link, I need to dig more from this website. Never found this article before.
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Unread postAuthor: Big-E » Mon Apr 27, 2009 3:16 pm

Yes, I know first hand because I basically built one of these form different parts off daisy guns. I believe it's a buck (or similar model) but I added stock & foregrip from a late 60's red ryder. I had to fabricate a new cocking lever since the old one broke. I had this since I was 12 I think; still shoots great!

Image

I believe Diana makes a bb gun as well, it's consisdered among the best, as they are used in shooting galleries.

Spring piston rifles that fire pellets never use a catapult; it would cause the skirt of the pellet to possibly jam. being pushed into the bore gently by a bolt; that's another story.

BB guns have fired steel shot (.177 caliber, actually a little smaller) for many years now, but pre WWII, they fired lead shot. only round ball ammo can be fired from one of these, and the ammo must be solid.
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Last edited by Big-E on Mon Apr 27, 2009 3:39 pm, edited 5 times in total.
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