Air Powered Rocket Launcher

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Introduction: Air Powered Rocket Launcher

In this Instructable I'll walk you through how to build an awesome air powered rocket launcher that can shoot paper rockets well over one hundred feet high. Parents and children alike always love building and launching the rockets. We take them to air shows and STEM events to help teach kids about aerodynamics. I designed these to be cheap, tough, and easy to use.

The frame price is a little over $50 for a launcher, but this can be reduced when building multiple launchers.

This short video explains the reasons for my design decisions:

I made a very detailed video on how to build a launcher, but since it is such a long video, I made this tutorial as well since seeing the steps one at a time is sometimes easier. If you have any questions, more than likely they are in this video. Or if you just prefer video instructions, take a look here:

Supplies:

I found most of the parts at Lowe's. With the exception of the Tee connectors and the SCH80 nipples, everything else was available at Home Depot as well.

See the attached parts list for URLs and more detail. It is a PDF so you can print it out when going to the store to pick up the items.

Parts:

  • 36 inches of 2 inch diameter pressure PVC
  • 4x 2 inch pressure PVC 90 degree elbows
  • 2 inch smooth to 1 inch threaded Tee pressure PVC connector
  • 2 inch smooth to 3/4 inch threaded Tee pressure PVC connector
  • 1 inch threaded PVC plug
  • 3/4 inch by 1 1/8 inch threaded SCH 80 nipple
  • These were hard to find. Only one of the local Lowe's had them.
  • 3/4 inch sprinkler valve
  • 3/4 inch threaded street elbow3/4 inch threaded to 1/2 inch smooth PVC adapter
  • 17 inches of 1/2 inch pressure PVC
  • 8 inches of 1.25 inch diameter PVC pipe
  • 2x 1.25 inch PVC caps
  • 20 feet of 18 gauge speaker wire
  • 3x 9v battery connectors
  • 3x 9v batteries
  • A button
  • 2x 2 pin electrical connectors
  • Valve stem
    • The best local place I had was Autozone (part # 20128)
    • Slime TR416 High Performance Valve Stems
  • Bicycle pump

Tools:

  • Drill
  • 1/8 inch drill bit
  • 1/4 inch drill bit
  • 1/2 inch drill bit
  • Miter saw or hack saw
  • PVC primer and cement
  • 120 grit sand paper
  • Thread tape
  • Electrical tape
  • Tape measure

Teacher Notes

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Step 1: Cut the PVC Pipes to Size

  1. Cut four 2.5 inch long pieces of 2 inch pressure PVC pipe.
    1. Measure the inside of the sockets. For the Ts and elbows that I used, the depth of each was 1.25 inches. Double the length to figure out how long to make yours.
    2. Use a piece of wood with a clamp to use as an end-stop. on a miter saw. This makes it much easier to four short pieces of PVC that are all the same size.
    3. Push the PVC up against the wood, and then cut the pipe.
      • If using an electric miter saw, we found it best to put the PVC in place, start the saw off of the PVC, bring the saw down through the pipe, and then leave the saw down until the blade has stopped. Otherwise the blade could chip the pipe.
  2. Cut two 13 inch long pieces of 2 inch pressure PVC pipe. These will make up the main portion of the compression chamber.
  3. Cut a 17 inch long 1/2 inch pressure PVC for the launch tube. The launch tubes length doesn't matter much, but I made it this size to prevent it from being longer than the total length of the air chamber.

Step 2: Install Valve Stem

You will need:

  • Power drill
  • 1/8th inch drill bit
  • 1/2 inch drill bit
  • Threaded PVC plug
  • Valve stem

If you're using a 3/4 inch sprinkler valve, then use a 1 inch threaded PVC plug. If you are opting for a bigger 1 inch sprinkler valve, then use a 3/4 inch threaded PVC plug. Start by finding the center of the PVC plug and drill a hole with the smaller drill bit. The size doesn't matter, it is just to keep the bigger drill bit from walking.

Using the smaller hole as a guide, drill the 1/2 inch hole.

Clean up the hole with a reamer or some sand paper.

Install the valve stem and ensure that there is a good seal.

Video Instructions: Install Valve Stem

Step 3: Sand All of the Glue Joints

  • Lightly sand the outside of the connectors.
  • Sand the inside of the sockets.
  • I used 120 grit sandpaper.
  • The sanded parts should no longer be shiny.
  • This helps the glue join the pieces together.
  • Don't forget to sand about an inch on one side of the launch tube, and then sand the inside of the 3/4 inch to 1/2 inch connector.

Video Instructions: Sand all the PVC

Step 4: Prepare to Glue Connections


  • Only glue the pieces in a well ventilated area.
  • Do a loose dry fit of all the pieces. It's much easier to fix things now.
  • Lay down something over your work area to to protect it from the primer and glue. I used a trash bag cut open.
  • Make sure all of your pieces are close by and ready to join.
  • Have some paper towels on hand to wipe up excess glue or primer.

Video Instructions: Prepare to Glue Connections

Step 5: Glue First Short Connector to Tee

  1. Start with priming the joints. Prime the entire joint surface on both the male and female side.
  2. While the primer is still wet, apply the glue to both sides.
  3. Quickly insert the connector into the Tee, twisting a quarter turn while pushing the pieces together.
  4. Hold the pieces together firmly for 10 seconds while the glue sets. If you don't hold the pieces pushed together, they will push apart!
  5. Use some paper towel to clean up any excess primer and glue around the joint.

First Detailed Gluing Instructions (gluing an elbow in the video, not the Tee):
Glue an Elbow to Each 13 Inch Pipe

Step 6: Glue the Other Connectors to the Tees

The 3/4 inch Tee is slightly shorter than the 1 inch Tee, but that's okay.

Video Instructions: Glue the Other Connectors to the Tees

Step 7: Glue an Elbow to Each 13 Inch Pipe

  1. Only glue an elbow to one side of each pipe!
  2. Glue the launch tube to the 3/4 inch to 1/2 inch adapter.

Video Instructions: Glue an Elbow to Each 13 Inch Pipe

Step 8: Join the Elbowed Tubes to the 3/4 Inch Tee

  1. This step can be tricky! Watch the video for clarification if you're unclear on anything.
  2. Screw the launch tube into the 3/4 inch Tee. Use this to make sure the Tee is lined up with the 13 inch tube correctly.
  3. Glue one of the elbows to the Tee.
  4. Push the pieces firmly together, and make the launch tube parallel with the 13 inch tube.
  5. Glue the other elbowed tube to the Tee, and use the table to keep the frame even.

Video Instructions: Join the Elbowed Tubes to the 3/4 Inch Tee

Step 9: Glue the Other Two Elbows to the 1 Inch Tee

  • This side is harder to get exactly right, but since I am using it for the valve stem, it doesn't have to be perfectly parallel with the frame tubes.
  • After gluing one elbow to the Tee, the already assembled frame can be used to help align the next elbow.

Video Instructions: Glue the Other Two Elbows to the 1 Inch Tee

Step 10: Glue the Two Frame Pieces Together

  • This is the hardest joint! Both pieces need to be glued at the same time, so it must be done quickly and it takes a lot of force to get both of the elbows onto the frame tubes.
  • Apply the primer to all pieces first, and then the glue.
  • After inserting the frame tubes into the elbows, I placed one end of the frame onto the floor, and pushed with all my weight on the other side to make sure both tubes go all the way into the elbow connectors.

Video Instructions: Glue the Two Frame Pieces Together

Step 11: Install the Valve Stem Plug

  1. Get the valve stem plug and some thread tape.
  2. Thread tape MUST be used!
  3. Wrap the thread tape around the threads of the plug in a clockwise direction. Wrapping around clockwise makes it so that the thread tape won't unwind when screwing the pieces together. Make sure to cover all the threads! This will help seal the plug and lessens the friction on the threads to prevent damaging the PVC.
  4. Screw the plug into the T. Don't over tighten, but make sure there is a good seal.

Video Instructions: Install the Valve Stem Plug

Step 12: Install the Sprinkler Valve

  1. Wrap thread tape around the 3/4 inch nipple.
    • Wrap it halfway down clockwise, and then flip the nipple over and wrap clockwise from the other side.
  2. Lightly screw the nipple into the T. No need to tighten it all the way because you will use the sprinkler valve to tighten it the rest of the way.
  3. Take the solenoid off of the sprinkler valve to make it shorter.
  4. Screw the sprinkler valve onto the threaded nipple.
  5. Reinstall the solenoid.

Video Instructions: Install the Sprinkler Valve

Step 13: Install Street Elbow and Launch Tube

  1. Wrap thread tape around the male end of street elbow.
  2. Screw it into the sprinkler valve.
  3. Wrap thread tape around the male end of the 3/4 inch to 1/2 inch adapter on the launch tube.
  4. Lightly screw the launch tube into the street elbow. This will need to be easily unscrewed later to transport the launcher.

Video Instructions: Install Street Elbow and Launch Tube

Step 14: Pressure Test the Launcher

  1. AFTER a few hours, the glue should be fully set. It only takes a couple minutes for the glue to hold, but it doesn't hurt to be cautious.
  2. Attach a bicycle pump to the valve stem and pump the air chamber up to 30 PSI.
  3. Check for leaks.
  4. Do NOT use the launcher in the cold. PVC becomes brittle when it gets cold, and it does not fail in a graceful way.

Video Instructions: Pressure Test the Launcher

Step 15: Build the Launch Button

This step shows how to make a launch button that will clip into the 3D printed holders, but the first launchers used a button assembly I found on Amazon that has an "arming" key and a big red button. I've included some pictures of how I assembled it.

  1. Wire three 9 volt battery connectors together in series.
    • Connect the first positive connector to the negative of the second.
    • Use electrical tape or heat shrink tubing to keep the between the two.
    • Connect the positive of the second connector to the negative of the third.
    • This adds the three 9v batteries together to make 27 volts total.
  2. Wire the button to the positive side of the three 9v connectors.
  3. Connect the positive side of the speaker wire to the other side of the button.
  4. Connect the negative side of the speaker wire to the negative of the 9v connectors.
  5. Cut the 1 1/4 PVC pipe down to 8 inches long.
  6. Drill a small hole in the middle of the 1.25 inch pipe for the speaker wire.
  7. Drill a hole in a the 1.25 inch PVC cap for the button. The size needed will be different for whichever button you use.
  8. Put the speaker wire inside the pipe and through the small hole.
  9. Connect 3 9v batteries to the connectors, and put the batteries into the pipe. Put the 1.25 inch caps on the pipe to protect all the batteries inside. No glue is required because you'll need to change the batteries eventually.
  10. Connect the speaker wires to the sprinkler valve. The positive and negative do not matter for the valve.
  11. Make sure there is nothing directly over the launch tube. Test the button. You should hear the solenoid on the sprinkler valve click.

Step 16: Build a Paper Rocket

  1. Wrap a piece of paper around a piece of 1/2 inch pipe.
    • When we take the launchers to events, we have a lot of small 1/2 inch pipes at the tables so a lot of children can make rockets at the same time.
  2. Use tape to keep the paper from unwrapping.
  3. Tape over one end of the paper tube to hold in the air.
  4. That's it! The rest is up to you. Add fins, a nose cone, paint, glitter, whatever! It's up to you.
    • If you're doing an event for a bunch of people, then having some nose cone and fin templates printed out ahead of time really helps out.

Step 17: 3D Print Brace and Holder (optional)

This is not needed, but it does make it easier to transport the launcher, and helps reinforce the sprinkler valve. If you have easy access to a 3D printer, then this is a great way to add to the build.

The valve brace relieves any stress that might happen to the sprinkler valve connections, and will help make the launcher last longer.

The launch tube and launch button holder just makes all of the parts one piece so that it's easier to carry. I used hose clamps to hold the holders onto the frame tubes, but zipties would probably work as well.

Video Instruction: 3D Print Brace and Holder

Step 18: Launch!

  • Always wear safety goggles!
  • Only use the launcher in warm weather!
    • PVC will get brittle if it's cold.
    • PVC does not fail gracefully!
  • Always use thread tape on the threaded PVC connections!
    • Thread tape seals the connection and helps reduce friction in the joint so it's easier to turn
  • Only put the paper rocket on when there is no pressure in the tank.

1 Person Made This Project!

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8 Discussions

0
ringworld
ringworld

Question 1 day ago

Great idea. Love the fact that kids can walk all over it without damaging it too much. And on behalf of Pack 785, we now have a great way to attract new scouts to our troop. Wonderful project!
Just wanted to point out you could use 3/4" Nipples to join the solenoid valve to the body of the unit and the launch tube. They are found in irrigation.
I used a simple strap and a 1"x2" piece of wood to secure the solenoid valve and keep it level with the rest of the body.
To save on tape we use 2" packing tape to secure the body of the rocket and nose cone.
We use the same 2" packing tape AND a square piece of paper on one end of the tube to ensure a consistent and air tight seal for launch.

Only issue is the 9v battery life. With 3 batteries in series from my test it only lasted for a day (4 hours). That can get pretty expensive considering.
Also to promote safety I added a "dad's" momentary switch to prevent premature launches in addition to the launch momentary switch. But I noticed that the line holds a residual charge. Any idea how to dissipate that? Not an EE and I thought a simple DC circuit would discharge. Any ideas?

0
krr711
krr711

12 days ago

You did a lot of thinking and polishing of concept for this to turn out this great! Thank you!

0
kotaquad
kotaquad

Reply 12 days ago

No problem! I have spent a fair amount of time standing in the plumbing aisle staring at all the pieces... :)

1
aaron.linker
aaron.linker

12 days ago on Step 18

Might want to consider adding a pop off safety valve and pressure gauge. I have had students the would pump until they couldn't anymore so a 80 psi pop off would keep a kid from pressurizing the system to the point of failure. And the gauge allowed them to monitor the pressure and make observations about launches at different pressures

0
kotaquad
kotaquad

Reply 12 days ago

Yes, that's a great idea! I looked at them, and the price was the main reason I didn't include them in this build. All of the bike pumps we've been using have gauges built in, so we have the students use them (also the younger groups we always have an adult helping them). The sprinkler valve is the weak link for this size pipe, and it is rated for 150 PSI I think.
If I were to add a blow off, I would probably put it with the valve stem connection. Thank you for the suggestion!

0
kotaquad
kotaquad

Answer 15 days ago

What part is broken? It depends on how much you have glued. Once a part is glued, you can't undo it.

0
seamster
seamster

15 days ago

Excellent work! : )