Pneumatic Rocket Launcher

On May 29, 2011 Ellery and I built a pneumatic rocket launcher.  This rocket launcher is powered only on compressed air and shoots rockets that are made only out of paper and tape!  The idea came from a project we saw at this year’s Makerfaire.  We found the exact project on Make’s website and followed most of the instructions there to build this.

 

Above is an image of most of the parts used to build this rocket launcher.  Most of them are just PVC pipe and fittings.  Some trickier parts to find are the brass adapters.  The screw in Shrader valve (tire valve) was the most difficult to find.  I couldn’t find any at my local hardware stores but luckily I had an older one lying around that I found at Ace Hardware a few years ago.  Another part to take note of is the green sprinkler valve.  The valve is activated with 24V DC power.  It has 3/4″ threaded openings on either side.

Most of this build is completed by simply using PVC primer and cement to glue together the PVC parts.  2″ Diameter tubing is used for the air chamber.  We used a section that is about 10″ long.  A 2″ End cap is glued to one end and a 2″ slip T connector is on the other end.

A 2″ to 3/4″ PVC slip coupling is glued to the top portion of the T adapter.  A 3″ piece of 3/4″ PVC is then glued to the coupling.  Finally, a 3/4″ female slip to 3/4″ threaded adapter is attached to the 3/4″ pipe.  This reason for this part of the assembly is simply to be able to attach the sprinkler valve to the PVC tank we had already created.  This could probably be done several ways, but this method seemed to be simple and worked well.

A 2″ slip to 3/4″ slip coupling is attached to the third side of the 2″ T connector.  Inside of that, we glued a 3/4″ slip to 3/4″ threaded adapter.  The purpose of the adapter was to allow us to thread in the threaded brass reducer.

 

The Shrader valve allows us to hook up an ordinary bicycle pump up to the rocket launcher very easily.  It should also allow us to attack an air compressor.  In the above picture, the Shrader valve is screwed into a 3/4″ to 1/2″ adapter.  The adapter is required because the PVC coupling is 3/4″ but the Shrader valve threads are 1/2″.  We wrapped all threads in Teflon tape to prevent air from leaking.

To attach the Shrader valve to the air tank, all we had to do was thread it in place.  We made sure it was nice and tight but not so tight that the brass threads tore up the PVC threads.

To attach the sprinkler valve to the air tank, just wrap the threaded part on top of the tank with Teflon tape and screw the sprinkler valve on.  Make sure the tank is attached to the input side of the sprinkler valve.  I’m not sure what would happen if it were installed backwards and I didn’t care enough to find out.

To make the barrel of the launcher we just cut about a 16″ piece of 1/2″ PVC pipe.  The air rocket template is designed for 1/2″ pipe.  You could probably make a bigger one but you would have to scale up the template.  To get the barrel to attach to the sprinkler valve, we glued a 1/2″ female slip to 3/4″ male slip adapter to the 16″ piece of pipe.  From there, we glued a 3/4″ female slip to 3/4″ male threaded adapter.  This allows us to screw the barrel on and off of the sprinkler valve easily so we can replace it if necessary.

To attach the barrel, we just wrapped the threads on it in Teflon tape and screwed it onto the other side of the sprinkler valve.  After that, we were done with all of the PVC gluing.

The next step was to make the launch switch (pictured above).

 

 

First we found a small momentary pushbutton switch.  The switch has to complete the circuit while the button is held down, but not complete the circuit when the button is not pressed.  Once we chose the switch we used a drill press to drill a hole to fit the button snugly.  The key do drilling large holes in PVC pipe is to start with a small drill bit and slowly work your way up.  If you try to drill a huge hole right off the bat, the bit tends to catch and just rip huge chunks off of the pipe which can be dangerous and destroy the part.  It is definitely a good idea to take your time and work the size up slowly.

We cut two wires each about 5 feet long.  These wires will connect the launch switch to the sprinkler valve.  We wanted them to be long enough that whoever launches the rocket can stand back a safe distance when it is fired.  We soldered one end of each wire to each lead on the switch.

We used heat shrink tubing to insulate and protect the solder joints.  You could use electrical tape or something similar but heat shrink is stronger and more reliable.  It just needs a heat source to shrink the tubing.  We used the middle of the soldering iron to heat up the tubing and shrink it.

Next we threaded the wires through the PVC end cap we drilled out and got the switch fit into place nice and snug.  We hot glued it in place from the inside so it would look nice on the outside.

Next we had to drill a smaller hole in the other PVC end cap.  This hole allows the two stranded wires to exit the launch switch housing.

All we had to do at this point was slide all of the pieces together and thread the wires through the small hole.  We didn’t bother gluing any of this together since it won’t get tossed around much.  This also allows us to fix any problems that may arise later.  We have also considered adding a second switch as a safety mechanism but we haven’t been motivated enough yet.  The next piece of this puzzle is the power source.

The solenoid valve says it requires 24 volts to trigger properly.  An easy solution to this problem is to just use three 9 volt batteries wired in series.  This should get us to 27 volts and is plenty of power.  I have actually heard that you can just use 18 volts but we used three batteries just to be safe.  I had a small empty Sparkfun box laying around and it happened to fit the three 9 volt batteries pretty snug so we used that as our battery case.  Hurray for recycling!  Next we had to attach all of the electronic pieces together.

We didn’t want to solder everything together since we might want to reuse the battery pack or the launch switch for other projects in the future.  We also didn’t have any good connectors laying around so we just used some classy jumper cables to hook everything up together.  Just make sure the cables can’t short together or you might accidentally launch the rocket when you don’t mean to.  For example when you are pumping up the air chamber and your face is directly over the barrel (not that this happened to me or anything).  Finally we had to come up with a way to attach everything together and keep the barrel aimed at the sky.

I had some wood scraps left over from a delivery pallet and one of them just so happened to be a good shape to make a simple stand.  We used two pipe clamps to clamp the launcher to the wooden brace.  The brace seems to work fine, although it would be nice to be able to set the launcher at an angle if we wanted.

Now that the launcher was completed, we had to build a rocket.  The template can be downloaded from Make’s website for free.  It is designed to be printed on legal paper and will not fit properly on normal 8 1/2″ by 11″ paper.  I was able to get it to work by rotating the image around and printing it in both landscape mode and portrait mode.  Just make sure the image is scaled 100% before printing or the dimensions will be wrong.   I’m not going to go into how to assemble the rocket here because I think that is pretty simple to figure out on your own.  All you need is paper, some tape and a pair of scissors and you are set.

So, does it work?

 

Heck yes it works! These rockets go high! Much higher than most people expect since the rockets are made of just paper and tape. I noticed that once you hit about 115 PSI on the air tank I don’t notice a big change in height. This may be because I’m right underneath the rocket so it is difficult to judge height. The highest I’ve pressurized the tank to so far is 150 PSI. I wouldn’t recommend going much higher than that since PVC pipe is not meant for air pressure and it splinters into shards when it ruptures. That can be very hazardous to the health of anyone standing near (like the person furiously pumping with a bicycle pump). You can mitigate this risk by wrapping the tank in duct tape.

For about $30 with of parts this project was well worth the time and money. I’ve already used it a bunch of times and everyone loves it. I also like that people can build their own rockets inexpensively in about 15 minutes and they can experiment with different designs. I highly recommend this project to anyone who likes to have fun and make things.