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We wanted to build a paper rocket launcher similar to that in Make magazine except entirely kid-powered, safe, and able to run all day long for fairs and festivals.  This design has at least 1000 launches in heat and dust and can launch a rocket made from a single sheet of copier paper and 12" of clear tape; sending it close to 100 feet aloft if carefully made.  Poorly made rockets fizzle or sometimes explode with a loud BANG on the launchpad which also causes much excitement.

The control panel has a hand-crank generator, electronics to store the charge, an LED to show readiness, a safety switch, and a launch button. Having all these bits and the 3-2-1 countdown really builds the suspense.

Step 1: Launch Tower

Materials for Launch pad

2 feet 1/2" pvc pipe
3 feet 3/4" pvc pipe
pvc fittings as shown in pictures
schrader valve for car tire
3/4" straight sprinkler valve
30-50 feet of 1/4" Polyethylene drip irrigation tubing
4 feet 1/2" galvanized pipe
1/2" galvanized flange
2'x3' 1/2" plywood (approximately)
2 push-to-connect tube fittings 1/4" tube to 1/4" pipe thread - mcmaster.com part #51025K178
bicycle pump

Start by assembling the sprinkler valve with the fittings as shown. You will need to drill a hole in the end cap that leads to the pump. Put the push-to connect fitting in that end cap. This is where you can connect your drip irrigation pipe. This sprinkler pipe will connect to a short length of pvc pipe with caps on both ends. The second push to connect valve goes on one end and the Schrader valve goes on the other end.  The Schrader valve connects to the bicycle pump. The drip pipe should be long enough so that kids can safely launch their rockets. A 3/4" pvc pipe with a cap on the end is added to the bottom of the sprinkler valve assembly. This is where the compressed air is stored until the launch button is pressed. Another length of 1/2" pipe is attached to the top of the assembly. This is where you mount your rocket. Screw the galvanized flange into the middle of the plywood. Screw the galvanized pipe into the flange. This will give you a sturdy place to attach your sprinkler valve assembly. Wood spacers and hose clamps were used in this case.

Step 2: Control Board

Materials need for control board

plywood or pressboard 2'x3'
wood 1/2" x 2" x 10ft
large video game button
toggle switch with safety cover
panel mount red led
16 gauge stranded wire - 30-50 feet
hand crank generator
plastic container to protect electronics
circuit board to control led light
2 sets of 1/8" inline headphone jack and plug for disconnecting wire
generator handle and knob made out of wood, metal or plastic

Build your control panel top out of wood. Figure out where you want to mount your crank handle, buttons, switches and light. Drill holes and mount all components. Make a crank handle for the generator. This one is made out of plastic but wood or metal can be used.  A knob at the end makes it easy to turn. The front side can be painted however you desire. A workmate table worked great to hold the control panel.

Step 3: Electronics

The DC generator stores charge in 3 10000uF capacitors.  The LED light goes on solid when there is enough voltage stored, then goes to blinking when it is a little weak, then dark if there is not enough. Attached is the schematic and PCB layout files for the design.

Parts List

1       0.1uF         capacitor
1       1uF            capacitor
2       1A fast recovery  diode
1       LM339N dip14
1      78L05  TO92  
1       220k 1/4W   resistor
1       2.2k  1/4W   resistor    
2       10k   1/4W   resistor    
1       4.7k  1/4W   resistor    
1       1M    1/4W   resistor    
2       390k 1/4W  resistor    
1       150k 1/4W  resistor    
1      330    1/4W  resistor    
1      10k     1/4W resistor    
1       0.1" 6 position screw terminal

Assembly
I just etched a single sided board for the circuit and another just for the capacitors.
  1. Connect the generator so that clockwise turning charges the circuit.
  2. Connect the LED with the correct polarity
  3. Connect the capacitor board to the main board with the correct polarity
  4. Connect the solenoid with the safety switch and pushbutton in series. Polarity is not important

Step 4: Rocket Design

Materials for Rocket Making

81/2"x11" piece of paper
scissors
tape
1/2" pvc pipe

Making a rocket out of one piece of paper is the challenge we like to use. Cutting a strip off before rolling up the rocket body seems to work the best. The smaller piece can be used to make fins.  Use the larger piece of paper to wrap around the pvc pipe. You can have a long rocket or a short rocket. Tape the whole edge of the rocket so no air can escape.  Twisting one end of tube of paper makes the best nose cone. Tape well the end so no air can escape. Use the smaller piece of paper to make fins. Tape those on to the body of the rocket. Now your rocket is ready to test.

Step 5: Fire

Launching Rocket

Pump the bicycle pump to build up pressure. A pump with a pressure gauge works the best. This allows kids to see what happens at different pressures. If you pump to much your rocket will explode on the launch pad. After you have the desired pressure you turn the handle on the generator until the LED light goes on. This means you have enough power to activate the solenoid. To arm, lift the safety cover on the toggle switch and switch it on. This means the launch pad is live. This is also a good safety device. After a count down you press the button and off goes the rocket!
Fantastic Generator! I have engineered a much different launcher with the same principles and have used 2 nine volts as a power source for launching with my 5th graders. How much fun is this! I am on the build now to add this great fun to the project I do with my kids to test newtons laws of inertia. Cheers
Very interesting, complete and prolix instructable!

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