Model rocket fired from a paintball gun

[Sillychris]

I have some 68 caliber dowel which fits a paintball gun very well. The plan is to fit some of this dowel as a rocket and fire it from the paintball gun... because Canada's cold. The thing I haven't come up with is how to ignite the engine upon firing. I'd like to utilize the firing pressure to close an electric switch.

Ideas?

[Winter Man]

Well if you're really set on it, ring contacts (like a DC motor) around the rocket with an embedded igniter. Stick a 9V in the grip and a microswitch behind the trigger, with a slide switch somewhere (with an LED) on the receiver acting as a safety.

[magnemoe]

Same way you launch ballistic missiles from submarines however I think they use some reaction to make the pressure.

As a kid we found you could increase the speed of firework rockets by launching them from an pipe who was closed in the back, you put pipes in ground to fire the rockets, if you dropped an small rocket down the pipe it started with far higher speed as the rocket exhaust pushed the rocket out, pipe was not an thigh fit.

[K^2]

Firing engines while in the barrel will increase the pressure, potentially, beyond what barrel can handle. This can be avoided with a delay, though. I'm also pretty sure the whole thing violates model rocketry regs in the States. Whether that causes any legal problems is up to jurisdiction. I have no idea how that works in Canada, but you might want to check.

That said, forget electrical ignition. This is practically a mortar to begin with, so there is no reason not to make it more like one. Use some of that dowel to make a plunger with a firing pin. Put a primer cap from a rifle shell at the base of the engine.^* This can work with or without a delay fuse, depending on whether you want the engine to fire in the barrel.

^* Again, I don't know how readily ammunition is available where you live, but you can usually get some short .22 rounds used for biathlon pretty much anywhere. Otherwise, primers aren't that hard to make. The home made ones just aren't going to be as reliable and stable.

[Seret]

Please don't disassemble cartridges to extract primers. You can just buy the primers on their own. Reloaders use them.

To get maximum effectiveness you'll need to find some way of providing a good gas seal inside the barrel. You could try a drive ring made from a soft material like copper or plastic which is expanded to bite into the barrel wall by the gas pressure. This is called obturation, there's a lot of different ways to achieve it, have a bit of a play and see what works for your setup.

[Aghanim]

If lets say we change the paintball gun to a coilgun will that thing works to ignite the rocket?

[goldenpeach]

Are you sure it's a good idea to fire a rocket from a paintball gun?

Will you be away when it fire or you will be holding the paintball gun when the rocket is launched?

Remember that,even if real isn't KSP, tour rocket could still go jebby.

[Sillychris]

Are you sure it's a good idea to fire a rocket from a paintball gun?

Of course it's not a good idea! That's why I'm doing it.

The electrical igniters take a a tiny bit of time (maybe half a second) to ignite the engine. That way the rocket will be clear of the barrel when it ignites.

Ideally, I'd like the ignition battery to be at the base of the rocket. That way it rides with the rocket until ignition occurs.

[magnemoe]

Firing engines while in the barrel will increase the pressure, potentially, beyond what barrel can handle. This can be avoided with a delay, though. I'm also pretty sure the whole thing violates model rocketry regs in the States. Whether that causes any legal problems is up to jurisdiction. I have no idea how that works in Canada, but you might want to check.

That said, forget electrical ignition. This is practically a mortar to begin with, so there is no reason not to make it more like one. Use some of that dowel to make a plunger with a firing pin. Put a primer cap from a rifle shell at the base of the engine.^* This can work with or without a delay fuse, depending on whether you want the engine to fire in the barrel.

^* Again, I don't know how readily ammunition is available where you live, but you can usually get some short .22 rounds used for biathlon pretty much anywhere. Otherwise, primers aren't that hard to make. The home made ones just aren't going to be as reliable and stable.

My method was far from an thigh fit, the pipe was so wide the firework rocket with pin fell down by itself, the problem here might be to high pressure in the rocket chamber as its designed to burn at 1 bar and not 2-3. afterwards I see this might have caused the charge to go off early, yes that we was using this to shoot at each other is more alarming

Dont see how this will work with an rocket with fins, so we are probably back to the orginal idea, use an paintball gun to push it, problem here is that the paintball gun is only designed to push 1 gram balls not an rocket 100 times heavier.

[-Velocity-]

How will the rocket maintain stable flight? You need some kind of fins or sticks off the back to keep it going straight. Otherwise, it could just turn around and hit you in the face. If it's going a few hundred miles per hour and has a pointy tip, that could be very, very bad for you.

What you need to do is first test your rocket design external to the gun, and make sure the design of the rocket itself is sound, and that it flies straight. The easiest way to test the stability of a rocket design is to tie the rocket on a string so that it's balanced about the point where it is tied. Then, spin the rocket around your head rapidly. If the rocket is stable, it will point into the direction of its spin.

Next, you should test the rocket in the gun without igniting the engine, several times. Make sure that the rocket maintains a straight flight after leaving the barrel!!!!

Only last should you combine the two... still not a safe idea though.

Anyway, as far as engine ignition, why not go simple? Maybe just use a fuse. Light the fuse, drop the rocket down the barrel, and then fire. If you time it right, then the engine will ignite while the rocket is still in the air. Just make sure to point it UP, so that the rocket is still pointing up when the engine ignites.

Edited April 7, 2014 by |Velocity|

[Sillychris]

How will the rocket maintain stable flight? You need some kind of fins or sticks off the back to keep it going straight. Otherwise, it could just turn around and hit you in the face. If it's going a few hundred miles per hour and has a pointy tip, that could be very, very bad for you.

What you need to do is first test your rocket design external to the gun, and make sure the design of the rocket itself is sound, and that it flies straight. The easiest way to test the stability of a rocket design is to tie the rocket on a string so that it's balanced about the point where it is tied. Then, spin the rocket around your head rapidly. If the rocket is stable, it will point into the direction of its spin.

Next, you should test the rocket in the gun without igniting the engine, several times. Make sure that the rocket maintains a straight flight after leaving the barrel!!!!

Only last should you combine the two... still not a safe idea though.

Anyway, as far as engine ignition, why not go simple? Maybe just use a fuse. Light the fuse, drop the rocket down the barrel, and then fire. If you time it right, then the engine will ignite while the rocket is still in the air. Just make sure to point it UP, so that the rocket is still pointing up when the engine ignites.

Your advice is wise, and I already have those details covered. I'm fairly experienced with rocketry and deploying it in non-conventional ways.

The only piece missing from my design is a method to close an electrical switch when pulling the trigger. I don't want anything connected to the paintball gun. I want an independent cartridge that can be primed, dropped down the barrel, and then fired at your leisure. What I need is a method for the co2 pressure to close a switch. I was wondering if anything out there exists already so I wouldn't have to fabricate it from scratch.

If you guys are curious of my application plans, I want to use this to deploy ropes to out of reach targets. And before everyone tells me rocket exhaust melts rope, don't worry. The lead line would be sacrificial and used strictly to hoist the actual rope.

[Sillychris]

I should also point out that initial testing of dry dowel rockets is extremely promising. They were puncturing 4 layers of corrugated cardboard and shown to be stable in parabolic flight. When an engine is added, that will obviously affect the center of mass and it may affect my fin placement... but probably not. A rocket engine is not sufficienty different in density from wood to affect the design very much.

You're obviously wondering how I place fins? Super simple. Rubber arrow fins glued to a portion of the dowel which has been sanded down. When the rocket escapes the barrel, the fins pop out. This also has the added benefit of moving the center of mass forward a bit.

[Razor235]

If you're really daring and/or stupid, you can try something the real Gyrojet weapons did, and modify the nozzle of the engine so that it has internal fins.

NOTE: This may or may not be illegal and incredibly dangerous.

[Sillychris]

If you're really daring and/or stupid, you can try something the real Gyrojet weapons did, and modify the nozzle of the engine so that it has internal fins.

NOTE: This may or may not be illegal and incredibly dangerous.

I am both daring and stupid. I really want one of those things now.

[Winter Man]

Something to keep in mind, you might want to port your barrel an inch or two in, give all that hot gas somewhere to escape. Don't want to have a CO2 tank (or anything else) blowing up on you when you melt the valves. Most rocket launchers are open tubes for this reason, the exhaust is completely vented out the back (also giving rise to the term 'recoil-less rifle').

[-Velocity-]

Your advice is wise, and I already have those details covered. I'm fairly experienced with rocketry and deploying it in non-conventional ways.

The only piece missing from my design is a method to close an electrical switch when pulling the trigger. I don't want anything connected to the paintball gun. I want an independent cartridge that can be primed, dropped down the barrel, and then fired at your leisure. What I need is a method for the co2 pressure to close a switch. I was wondering if anything out there exists already so I wouldn't have to fabricate it from scratch.

If you're using air pressure, you likely can't just have a plunger on the back that is not sealed against the inside of the barrel. Otherwise, the pressures on the back of the plunger will quickly equalize with those in front, and the plunger will not move.

What you might want to try is placing something (like a thin, breakable and breathable membrane) across the muzzle of the paint ball gun. You would place the ignition switch of the rocket on the NOSE of the rocket. It would be some kind of latched push-button. When the nose of the rocket strikes the membrane, it latches the switch closed. As the rocket continues out the tube, it breaks the membrane, and continues on its way, igniting the engine shortly thereafter.

The membrane must be breathable, otherwise the air pressure ahead of the rocket could break it before the rocket gets there.

Instead of a membrane, you could try a plastic cap with a bunch of holes in it. It fits snugly over the end of the barrel, snugly enough to stay on until the nose of the rocket strikes it. Also, tie a string to it, and tie the other end of the string to your gun. This way, you can easily recover the cap after firing.

An issue with the plastic cap however is the possibility it could get caught around the nose of your rocket and wrench the rocket into a spin. To solve this, instead of a cap, you could use simple some kind of plastic plate that locks in place over the barrel and just levers/flips back after the rocket strikes it.

Another safety issue is pushing the rocket down the barrel when the ignition switch is on the front. But this whole thing is highly unsafe. Just makes sure you don't LOOK down the barrel while your pushing the rocket down it.

Another idea I head was to use a photoresistor or photodiode as a sensor to detect when the rocket was outside of the dark barrel and into the brighter outside. You could even use an infrared photodiode that is only triggered by an array of IR LEDs at the end of your barrel (through bright sunlight would probably also be sufficient). But these ideas all require more electronics know-how than you probably possess. At the very least, the photoresistor/photodiode would need to be in a circuit that feeds a current/voltage into the base/gate of a BJT/MOSFET, with the transistor being used as a switch that conducts the comparatively high current required to ignite the igniter. If you're not an electrical engineer or electronics hobbyist, this stuff is probably beyond you.

Edited April 8, 2014 by |Velocity|

[K^2]

If you're using air pressure, you likely can't just have a plunger on the back that is not sealed against the inside of the barrel. Otherwise, the pressures on the back of the plunger will quickly equalize with those in front, and the plunger will not move.

The rocket doesn't need to sit tight with the muzzle. Plunger will push it mechanically just fine and to the same effect.

[MoniG]

I like the idea about fire a rocket from a paintballgun as much as i like my co2 sensor which keeps controll over me so that i dont suffocate in my own room.

[Sillychris]

Velocity, these are some really good suggestions. I particularly like your idea of a mechanical switch that works when the rocket leaves the barrel. I don't know why I was getting tunnel vision over the pressure activated switch.

I could do a spring loaded rocker style switch at the rear. As soon as the rocket leaves the barrel, the switch would be free to expand and therefore trigger.

I like your photodiode idea, too. Only problem with that is it might be tricky to arm before inserting.

I could also go super ultra simple and have a fishing wire pull out an insulator when the rocket is x feet away... maybe that's what I'll do for proof of concept...

This community never fails to impress me when I ask for help brainstorming.

[YourEverydayWaffle]

If the fuse is a soft black powder fuse, fold it forward and just put the rocket far forward in the barrel. See if you can turn up the velocity on the gun, so there might be a little more pressure to launch the rocket. Put some saran wrap over the nozzle to make sure none of the pounded powder gets cracked or dislodged. If the fuse is not very soft, just see if you can chisel a sort of groove in the edge of the rocket to put the fuse into so the end sticks out. Light it and wait till it's just about to go off and shoot the gun. Otherwise, there's gonna be huge trouble if the bolt mechanism gets hit by flame or too much smoke.

[Javster]

Of course it's not a good idea! That's why I'm doing it.

The electrical igniters take a a tiny bit of time (maybe half a second) to ignite the engine. That way the rocket will be clear of the barrel when it ignites.

Ideally, I'd like the ignition battery to be at the base of the rocket. That way it rides with the rocket until ignition occurs.

Don't die!! (it's bad for your health)