TF2 Direct Hit schematics

[ChriL]

here's the gun i hope to make soon. It's supposed to turn out as a replica of the Direct Hit from the game Team Fortress 2
any suggestions or pointers would be helpful 8)

link to my quick drawing~
http://www.facebook.com/photo.php?pid=3 ... 0896104340

[Insomniac]

So you're going to be setting it up as a coaxial combustion cannon? It looks workable, but not with that barrel placement... There is a severe flow restriction between the walls of the barrel and the narrower part of the chamber.

Is raw power a real goal with this, or is it more for the novelty of a functional replica? A coaxial piston valve could work well, if you kept the whole launcher in the wider section of the gun. You could use the narrower section to house, say, a paintball CO2 tank and regulator for an onboard air supply or something similar.

EDIT:

Also, make sure you use a decent scope... If you want that 25% damage boost, your going to have to be accurate.

[Gaderelguitarist]

Sadly it looks as though you've worked in several dwv fittings into your drawing. I would be very cautious with the use of these fittings, as they are not built for pressure handling.

[ChriL]

So you're going to be setting it up as a coaxial combustion cannon? It looks workable, but not with that barrel placement... There is a severe flow restriction between the walls of the barrel and the narrower part of the chamber.

Is raw power a real goal with this, or is it more for the novelty of a functional replica? A coaxial piston valve could work well, if you kept the whole launcher in the wider section of the gun. You could use the narrower section to house, say, a paintball CO2 tank and regulator for an onboard air supply or something similar.

EDIT:

Also, make sure you use a decent scope... If you want that 25% damage boost, your going to have to be accurate.

i was thinking 50% look 50% functionality
and i've tried my hand at a coaxial air cannon and failed horribly
and probably no scope lol

Sadly it looks as though you've worked in several dwv fittings into your drawing. I would be very cautious with the use of these fittings, as they are not built for pressure handling.

oh well, they seem to be working fine on my other canon (i havent displayed that at Spudfiles yet)

[Hotwired]

It's really the wrong way round for a full length barrel.

However if you accept that you can't get a long barrel in you can have a reasonable short barrel coaxial launcher and stuff the cannister of gas in the rear section of the launcher.

[ChriL]

It's really the wrong way round for a full length barrel.

However if you accept that you can't get a long barrel in you can have a reasonable short barrel coaxial launcher and stuff the cannister of gas in the rear section of the launcher.

ya, but it'd be cool to have a gun like the game.
i did the numbers and the barrel is about the right ratio to the chamber, but as Insomniac said, flow restrictions.

[Insomniac]

One other option, is to ditch the whole cannon idea, and turn it into a sort of shoulder mounted water rocket launcher. This gets rid of a bunch of problems in the design, and turns it into a genuine freakin' rocket launcher.

Oh, and if you use flour instead of water, it will look über cool.

[ChriL]

One other option, is to ditch the whole cannon idea, and turn it into a sort of shoulder mounted water rocket launcher. This gets rid of a bunch of problems in the design, and turns it into a genuine freakin' rocket launcher.

Oh, and if you use flour instead of water, it will look über cool.

that sounds..... freaking awesome!
how would i go about doing that?
to the google!

[saefroch]

The second link in Hotwired's sig.

[ChriL]

do you think making the rocket's propellant be combusting propane work like or better than the water/flour?

[saefroch]

I'm rather confused by your question, so I'll assume multiple possibilities. The compressed air that was fed into the rocket is the source of the propulsion, but it is aided by the greater density of water or even flour, but to a lesser degree. Using just a combustible mix won't propel the rocket very far. Replacing the compressed air with a propane/air mix probably wouldn't cause much of an overall performance difference.

[ChriL]

sorry for being vague.
i meant filling the bottle with propane, then igniting it.
right now i'm thinking that's more complicated than i'm willing to go for.

[saefroch]

That wouldn't behave much like a rocket, it's just sort of jump instead of really launching, due to the small momentum of the gases expanding out the nozzle.

[ChriL]

humm ok i'll keep that in mind...
But back to the combustion cannon, with all of your vast knowledge about spuddin, about how less power full would my idea be compared to a regular one. (maybe % wise) just some sort of quick estaminet.

and just another idea, what if i make the barrel in the smaller part of the gun shrink to 1.5" or 1" would that fix the air flow issues?

[Insomniac]

What you're thinking of is sometimes called a 'whoosh rocket'.
They don't go very far at all. Here's a video of me messing around with a small one for laughs. I don't think it ever managed to fly high enough to even hit the ceiling.

[youtube][/youtube]

The problem with these, in comparison to real liquid fuelled rockets, is that of energy density. Gaseous fuel does NOT hold an aweful lot of energy for its volume, which is why proper rockets use liquified gas.

Water rockets work by pressurising air (to provide the energy), and using it to expel water as a reaction mass. If you launch a water rocket using just air and no water, it won't go very far as the escaping air has very little momentum. The air being expelled out the back is going very quick, but it is very light. This results in an extremely short duration of thrust (the air is gone almost instantly), and the thrust you do get is very low.

Adding water (or flour, though it doesn't work as well) solves this problem. The first purpose of the water is to slow down the time it takes for the rocket to run out of propellent... The water can't flow out as fast as the air, so the thrust lasts for much longer. The second benefit is that the water being expelled has quite a lot of momentum. Due to Newton's 3rd law, this means quite a lot of force is applied on the rocket, which is why water rockets can produce such a high amount of thrust.



As for the original combustion idea.... Provided that you shorten the barrel to reduce flow, you're going to get quite a bit less power than a full size spudgun. The coaxial design is going to rob some power as well. However, it should still be enough to make an impressive BANG and shoot a projectile pretty quickly. Particularly if you use a chamber fan and propane metering system to try and compensate for the less than ideal shape.