I have been enamored with Air Rockets since the Makezine article was published http://makezine.com/2010/04/14/weekend-project-com...
There have been many versions since then but I wanted to make a system that was easy to set up, safe, and repeatable. I bring up safety because I have young kids and wanted to share this with their friends without issue.
My wife is an art teacher and I am the resident geek so I took this opportunity to bring a bit of science into the Art classroom.
Step 1: Basic Premis
The operation is simple. Fill a chamber with air and release it rapidly to launch. The best way to release quickly enough is a sprinkler valve. I went to my local home improvement place and found one on the clearance rack for $5. There was some expense on PVC and fittings, but the rest of the stuff came out of my garage and a trip to Radio Shack.
The rockets themselves are simple and quick to assemble. Reusable without heavy engineering was key as 6-year-olds are not known for their patience. For the classroom, expedience is always key.
Step 2: The Rockets
My addition to Air Rocket lore my rocket design. As with any engineering thought exercise, reality gets in the way of theory most occasions.
So to "KISS", I use paper towel tubes, plastic golf practice balls, masking tape, and a bit extra cardstock for fins. Once complete, the kids can decorate as desired with markers and stickers. (I'm kinda partial to googly eyes)
The golf ball fits nicely at the end and the masking tape does and excellent job creating the seal and holding the ball in place. Successive "landings" will deform the rocket but then just remove the ball and fins and add to new rocket body tube.
As with all rocketry, lighter the better.
Let the creativity begin!!
Step 3: The Launch Platform
Here is my platform packed and ready to load into the car. I'm not going to go into great detail on the BOM as that is part of the fun of building one. I 'bodged' mine together from what I saw in the other publications.
I use a bicycle pump to load the chamber. A compressor would be easier (and less strenuous on the body) but not as portable.
Air Chamber is 12" of 2" Schedule 40
Launch tube is 18-20" of 1" Schedule 40
The air connection is sink hose with a Shrader valve from a bicycle tube at the end with hose clamps to secure. Any threaded portions were teflon'd.
CAUTION: You are working with a good amount of pressure!! Glue things together according to directions and let dry overnight. Use your 'nugget'!! Get help from your resident geek if needed.
Step 4: "Button, Button. Who's Got the Button?"
To activate the solenoid inside the sprinkler valve typically calls for 24 VDC. For this project, 14.4 VDC works just fine and is easily found in the rechargeable battery of your choice of hand drill.
Here's the big safety bit... kids get excited when it comes to launching projectiles into the air at high velocity. This can lead to accidental discharge. Here is my solution:
Launch controls for regular model rockets have a battery in them to heat the igniter in the rocket engine and therefore has a safety switch that saves fingers and battery life.
I put this together with that in mind. It has a safe position and an armed position. This locks out the launch button while pumping or loading with a rocket.
One flips up the cover and moves the switch to the 'armed' position, which is indicated with a LED. The launch button can then be mashed to activate the solenoid.
Battery connections come in through the back and I use a CATV terminal on the front to connect a 15' length of TV cable to keep a safe distance away. This also allows for the CATV quick-connectors. The connections to the battery terminals are the large female type automotive connectors. Use a volt meter to determine which is + and - on the battery. The basic design can be seen in the attached sketch.
Step 5: The Complete Package
Connecting the "Button" to the valve with the battery. Arming the system. Loading a rocket. (I left the hose coiled up.)
Step 6: Rocket Operations
My kids and I operate out of Cape Driveway so we have a protocol:
Clearing the Range - no one coming down the sidewalk, no cars coming down the street
"Range is Cold" - Launch Safety is on (cover down) so that launchpad operations of loading a rocket and pumping can take place
Clearing the Range - Again, as a double check
"Range is Hot" - Launch Safety is off. Button is armed. Countdown and Fire!!
"Range is Cold" - Launch Safety is put back on for 'vehicle recovery'
Notes: I use about 70 PSI. This gives significant altitude without the risk of pressure induced failure of the rocket and risk of damage to the chamber.
The golf ball sits very nicely on the 1" coupler at the 'working end' of the launcher and provides a good seal on the paper towel tube to push the rocket. If the paper towel tube doesn't fit, the coupler can be removed as I didn't glue that one on.
Safety is highest priority but is easier to accomplish out in the ball field.
All the kids line up 10' away from the Launch Control which strung to full length away from the Launch Pad
Quick safety brief for the kids on where to stand, when to approach the Launch Control, waiting for the rocket to hit the ground before recovery, and good manners if one rocket doesn't go as high as another.
Acknowledgments: This is an awesome project! Hats off to whoever first conceived the idea. And Digi-Key's Scheme-It tool for the Launch Controller diagram
Let me know what you think.