SpudFiles

Hey guys, I'm not really sure if this is the right spot for this thread so if its needs moved then please do so.

At my school, im in physics. We are currently working on building egg launchers. The launcher itself has to fit inside a 3m x 3m square. We have to design a launcher that will fire an object that holds an egg intact 75 meters onto a bullseye. 1 meter wide. I'm mainly looking for suggestions or ideas or whatever you guys think will help. Based on what i have researched on here, i think we want to build a coaxial piston design.

The actual rules of the competition can be found here.
http://www.tech.purdue.edu/anderson/...elines2009.pdf

Thanks in advance!

hobodictator wrote:Based on what i have researched on here, i think we want to build a coaxial piston design.

That's probably too efficient for what you want to do, you want gentle acceleration so a relatively inefficient valve is best. Also, you want your projectile to be as aerodynamic and sectionally dense as possible, so it can travel far in spite of a low initial velocity.

The rules url is incomplete so I can't tell exactly what protective measures you can take with your egg. unless it's specifically not allowed, encasing it in expandable foam is the bare minimum of protection.

Sound like just about any type of launcher could work. An egg 75m is not that hard to do. (Though keeping it intact on landing is another matter.)

3m x 3m footprint means the barrel could be nearly 6m (~20') long (the diagonal of a 3x3x3 cube). With a barrel that long you really don't need a fast opening valve. Heck a 3/4" sprinkler valve is probably fast enough. Wouldn't even need to mod the valve.

The sabot (or carrier vehicle) is going to be critical as is reproducably setting the chamber pressure. A variation in chamber pressure of say 2 or 3 PSI will be enough to change the range by a meter or so. A generic pressure gauge, even a fairly pricey one, is not reproducable to say a half PSI, which is what you probably want. Even a regulator probably isn't that reproducable.

Depending on how many practice shots you get, I would say something like an over under design. Using a modded sprinkler valve you could have about a two foot by two inch barrel and chamber. At a 45 degree angle with 60 psi I would approximate around 75 meters. You could make it mortar style where you turn a crank to adjust for elevation and windage. Then your only problem would be getting the egg to leave the barrel safely and land safely...

One thing that might help you is shaking the egg before you launch it. It's a trick that a friend of mine showed me. If you shake an egg for 30 seconds or so before you throw it or launch it, it's slightly harder to crack.

hopefully Technician will drop by soon. IIRC, he was having success launch eggs around 200 yards. The idea is to use low pressure, high volume, and a slow valve. He did it with the QDV, but the fast opening time is not needed.

You could also hard-boil the egg, if that's not specifically banned.

WOW Thanks for all the respones so far, you guys are helping alot.
Heres the correct url for the rules http://www.tech.purdue.edu/Anderson/egg ... es2009.pdf

The egg cannot eb hard-boiled but I will make sure to try shaiking it first. Great tip. Our budget is around $75-100 for the entire project.

One question i have is: Should we design a launcher around the egg carrier or the egg carrier for the laucher?

The lower pressure idea sounds great also. I do have acces to paintball regualtors that are quite accurate and easily adjustable.

Thanks again for everything so far.

My first thought is a tubular projectile with the egg in the centre of a section of foam that fits exactly in the tube as a sort of piston. Between this piston and the nose of the projectile you could have some sort of spring which allows the piston to move forward as the projectile decelerates on impact.

The piston could be cast around the egg using expaning foam, then cut in half for easy access.

I would go for a 3" barrel, as long as you can make it to fit within the allowed area, and a relatively low flow valve like a 3/4" sprinkler valve. The idea here is that you achieve velocity using low pressure but a long barrel, and by keeping the valve electrically actuated you'd get more repeatability which will help with accuracy.

I'd personally go for an air piston. Simialar to JSR's design but have the egg travel down the tube during impact. Friction along the sidewalls will slow it down over a longer period of time. Depending on the seal on the egg, I may add a soft foam material similar to the density of egg crate (haha) foam in front of the egg for impact dampening as well.

you could make a discarding sabot you could just use a sprinkler valve

what about a bow and arrow make a specol arrow that u glue to the egg and bam done

Gosh i wish my school was this cool when i was a kid.

although.... i did manage to put a pencil into a locker from 20 feet away while "Showing" my projecy from home, to the physics teacher.... he laughed and told me i had an awesome linear excellent as "Guns" are forbidden in schools. hehehe

Enough of my ramble-rabble.

Go with JSRs design for the projectile a spring is FAR more reliable than an air piston when you are using something so imperfectally shaped as an egg.

Simply put.... do what every one here is saying.

An over under design, chamber connected to the barrel via a "U" shape leading the the valve.
Use the longest barrel that you can, and shoot with low pressures.


The only thing i can add, is possibly another spring behind the egg. so as to cradle the egg and actually suspend it inside foam casing that is inside the projectile.

Hope fully i was helpful, and not just a rambling fool

i didn't read what other people wrote, but I think you obviously need a fairly low pressure and also you need to use lots of wadding.

Twizi you've been told about this before.

you could make a discarding sabot you could just use a sprinkler valve

Why the hell discarding? The egg needs the gentlest deceleration as possible, you want to KEEP the sabot with the egg.

what about a bow and arrow make a specol arrow that u glue to the egg and bam done

An egg is rather heavy and un aerodynamic for a bow to launch.

It may make it hard to get onto the bullseye, but a parachute along with the other ideas here would make keeping the egg in one piece much easier- which should really take priority above hitting the target. Drag ribbons or flaps could also be deployed during flight.

This is the basic projectile concept I was describing:

If i were to make a gun to do that i would use a sprinkler valve or a ball valve actually. The slow opening time would give the egg a nice launch while if you had a big air chamber and a long barrel the air would increase the velocity as it slid along the barrel. then use something like JSR's projectile (above). For improved performance you could use a spring loaded ball valve to speed the opening time up.

PS:i'm jealous i want this class.