Build A Rocket Launcher For $20

Recently I was reviewing with a friend the modifications our family had made to the rocket launcher described in the Cheeto Cannonballs post. He asked how much it would cost for him to build a launcher. I thought that with some simplifications to the design I could probably build one for $20. This post is to document how to build a compressed air rocket launcher for $20.

Simplifications

I have learned a few things from the previous launchers I have built. First, the air reservoirs don't have to be very big. It doesn't take much air to push the rockets. Larger chambers take more work to fill, which is an issue if you are using a bike pump for pressure. A smaller reservoir also means less cost in materials.

Another simplification is to use the fewest number of parts. Some launcher designs have two reservoirs. The second tank looks cool but adds no functional value. Other designs have lots of pieces to reduce the diameter of the pipes. Each piece adds extra cost.

Also, I tried to use threaded connections whenever possible. Having threaded parts makes it easier to change the launcher afterwards (or fix mistakes).

Finally, many designs require legs or a stand for the launcher. This makes storage harder and requires more time to build and more money to buy the additional pieces. My launcher is in a U shape so no stand or legs are necessary.

Construction

Home Depot had pre-cut 2 foot sections of PVC pipe. I used a 1.25 inch pipe for the reservoir and a .5 inch pipe for the launch tube. I chose the cheapest automated valve I could find that had .75 inch couplings. Those three main parts form a U shape, with diameter reducing elbows between them.

Here are the parts I purchased.

Part	Price
3/4 inch GRN NPT JAR TOP VALVE	$10.94
1-1/4x2' PVC PIPE	$2.61
1/2"x2' PVC PIPE	$0.99
1-1/4" PVC Elbow 90D	$0.98
1-1/4" PVC CAP SLIP	$0.75
3/4"x2" PVC SCHDL 80 NIPPLE RISER	$0.49
3/4"x1/2" PVC BUSHING	$0.74
1/2" PVC STREET Elbow 90D	$0.63
1/4" NPT Male Connector	$1.59
Total	$19.72

Here are all of the parts laid out how they will be assembled. 

The first step was to drill a 1/4 inch hole into the end cap and we screwed the air connector piece directly into the cap. (Our launcher will be connected to a compressor. A valve stem could be place here if using a bike pump to compress the air.) Then we glued the fiew pieces together that weren't threaded.

 

Finally, we threaded in the sprinkler valve, covering the threads with teflon tape. An embossed arrow on the side of the valve indicates the direction the air should flow. The valve won't work if inserted backwards.

At this point we had a functional launcher for less than $20. All we had to do was touch the leads of the sprinkler value to a 9 volt battery and it worked. This is functional, but not practical. So, for a few extra dollars we added a launch button.

The launch button

We bought a small plastic box from a dollar store. From Radio Shack we purchased a push button momentary switch (4 switches for $3.39) and a pack of 9 volt battery connectors (5 for for $2.69). I drilled a quarter inch hole in the back of the case for the cord and one in the top for the button switch.

One battery will open the valve is the sprinkler leads are connected directly to the battery. But there is more voltage drop across the long connecting cord, so two batteries are required. The 9 volt batteries are wired in series, like this.

I used a long phone cord to connect the button to the sprinkler valve. I tied a knot in the cord inside the box so that pulling the cord doesn't put any stress on the switch. I used an Xacto knife to expose the wires in the phone cord and then spliced one end to the valve and the other to the battery leads.

This was our final launcher built for less than $20, and the launcher system which cost a few more dollars.

We quickly made the rocket in the photo out of paper, a file folder, and tape just to test the launcher. We also like to launch Cheetos! When we have a function that requires a lot of rockets, we usually buy the rocket bodies from It's a Blast.

Further Improvements

In this design the launcher is connected directly to an air compressor. When we actually used this launcher for an event we added a small hand valve so that if the launch button was held down it wouldn't drain the compressor tank.

This launcher works great and it doesn't cost a lot of money to build. It has provided hours of entertainment. 

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