Introduction: Compressed Air Launcher and Reusable Rockets
This project utilizes PVC, an automatic sprinkler valve, a bicycle pump and some household items to make a rocket launcher and rockets with flight characteristics comparable to single stage hobby rockets with solid fuel engines. Better yet the rockets are cheap, and the fuel is free!
Step 1: Supplies:
The Polyethylene Tubing, Hose Clamps and Bicycle Extension Hose are not required but if you want to pressurize the chamber from a distance. You can use this length of hose as opposed to standing right next to the pressure chamber. I did not show the assembly of this component as I seem to have misplaced it.
Step 2: Tools:
Saw: (hand saw, miter box or power miter saw) for cutting PVC
Saw: (Jig saw or coping saw for cutting circle in wood)
Drill and Bits
Screwdriver (for Hose Clamps if needed)
Soldering Iron or Wire Nuts
Hot Glue Gun and Glue Sticks
You will also need a pencil and/or marker
The first thing you want to do is drill a hole in one of the 2" caps for the tubeless valve stem. there should be a hole size indicated on the packaging. Or if not, either way you will want to start with a small bit and gradually move up in size to insure that you cut a clean, hole. PVC is soft and tends to tear if you try to drill too much at a once. Pull the valve stem through, it should take a bit of force. You may need pliers but use caution to avoid damaging the valve stem. Cut a couple 8" lengths out of the 2" PVC, cut the 1/2" to about 3'. Chamfer one end of the 1/2" PVC, This makes it easier to get the rockets on the end of the tube. Glue it all together per the diagram. Be liberal in the use of primer and glue. 2" Schedule 40 PVC is rated for up to 280 PSI (not that you should or will be pushing it that hard with a bicycle pump) but it is the joints and connections where the chamber is most likely to fail.
Note: in the diagram I show a 3/4" threaded coupling between the threaded 2" adapter and the automatic sprinkler valve. This would be the simplest connection. You can see in the pictures that I did not have this part so I had to improvise with a couple additional fittings that I did have.
Step 4: Base
Cut the 2 x 4 to the dimensions shown, Drill a hole through the shorter piece (or cut with jigsaw) a diameter that lets the 2" pvc cap slip snugly through. (> 2.5") Cut a slot near the top of the hole, drill a 1/4" hole laterally through the slot an put in your bolt and wing nut, this will allow you to fix the base to the air chamber, and adjust the trajectory of your rocket launches. I ripped the 16" base down to 1/2 the width of a 2 x 4 on the table saw to make it slimmer but this is not necessary. Screw the vertical section to the base using three screws. Make 2.
Step 5: The Rockets:
The rockets are made of fiber reinforced packaging tape. This tape is the only that I am aware of that is strong enough to resist the air pressures involved. Take a piece of paper (1/2 sheet 8 1/2" x 11") to act as a spacer, roll it tightly around your left over piece of 1/2" PVC and tape it in place with scotch tape. This first piece of paper acts as a spacer to make sure that your rocket tube is not too tight to the PVC after you wrap the tape. Cut a 1/2 sheet (approx 4 1/4" x 11" doesn't need to be exact) piece of transparency wrap it around the paper and hold it in place with a few pieces of scotch tape. Use the packaging tape and spirally wrap around the acetate roll, overlapping 1/2 to 1/3 of the width. It is hard to keep the wrinkles out as the the angle of the initial wrap seems to creep to zero as you go up, this is not critical, smooth these out as best you can. I used 1 1/2" tape, 2 1/2" might work better. BTW the photo above of the wrapping process does not show the paper spacer underneath. I had forgot this step when I took the photo. Trim off any excess and wrap a ring around both ends. I made three tubes for three rockets.
Note: paper could be used in lieu of the transparency sheets, it is the packaging tape and not the plastic sheets that give the rocket its strength. However the plastic sheets tend to hold together a little longer when repeatedly placing the rocket over the end of the tube. Also the paper tends to absorb moisture from the compressed air and the occasional wet grass when it lands and there is less friction between the plastic sheet and PVC than there is with the paper variety.
Step 6: The Rockets Cont: Shock Absorbing Nose Cone
Cut a nose cone out of packaging foam, shape a it to fit the end with a knife. The packaging material will act as shock absorber as it lands so you can reuse it many times or at least till it lands on a neighbors roof. Trim it to fit snugly in the end. I found that it was easier to shape the nose of the rocket with a pair of scissors. Cut a plug our of cardboard roughly the outside diameter of your 1/2" PVC. Put tube over your 1/2" PVC, and place the plug inside. Depending on how far your nose cone goes into the tube, this stop should be 1 1/2" or so from the end.
Pour in some glue, 1/4 to 3/8" of it. this not only holds your nose cone in place but becomes ballast weight for the top of your very light rocket. Push the nose cone in, forcing a little glue between the tube and the sides. BE CAREFUL!. this is the step where I have hot glued my fingers and hands several times.
Step 7: The Rocket Cont: Tail Fins:
Cut out 3 matching tail fins out of cardboard in you preferred shape, or if you want, out of a more durable material. Glue them parallel with the rocket, spaced 120 degrees apart, I used the edge of a book as a guide to draw parallel guide lines and eyeballed the 120 degrees, the eyeballing gets easier as you add fins. be liberal with the glue and give each fin a few extra seconds to dry, this will make them more rigid. You can add glue later but this will just melt the glue that is already there and it will become all floppy like you are glueing it on the first time.
Step 8: Fire Button and Batteries:
The Sprinkler Valve is triggered by 24V pulse but 18V from (2) 9V batteries wired in series will also trigger the valve. The sprinkler valve typically holds water under pressure in an underground sprinkler system, when voltage is applied the valve opens. We will be using it to hold compressed air rather than water. I put a momentary switch inside a 1/2" PVC Cap connected to 2 wires that then looped through two 9V batteries connected in series and the sprinkler valve. I used an empty baby food container to hold the 9V batteries and located them on the base rather than adjacent the switch in my hand. the wire between the switch is about 20' long so I can stand a ways back from the rocket before firing.
Step 9: Touch Up:
I painted the PVC with Fusion Plastic Paint and the rockets as well to make them look a little sharper.
Put some Teflon tape on the threads and screw it all together. Then find a big open space an go fire off some rockets! I have found that these go nearly as high per the naked eye as the hobby store solid rocket fuel variety. That is the ones with engines small enough that you will be able to find your rocket. I have tried unsuccessfully with twist timers and other devices to rig a parachute into the assembly just because it is fun to watch it come down, but it is not necessary to save the rocket as the light weight and foam nose cone protect it from being too damaged when it hits the ground. The air chamber is pretty small so it doesn't take too long to get it up to pressure with a bicycle pump. 10 pumps to get to 40 psi, 20 pumps to get you close to 80 etc. I have never attempted higer than 90 PSI but that is enough. A bicycle pump with a pressure dial is helpful. You could also add a pressure gauge to the air chamber by tapping and threading the PVC but that would add a weak point to the pressure tank. You could use an air compressor as well although its a bit scary and I would never do that without being able to monitor the pressure inside the PVC
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