A conventional model rocket engine is simple combustible solid fuel (black powder or more advanced composites) molded into a cylinder that uses expanding gas to produce thrust. Though it is minimal, there is some danger there. An alternative is compressed gas, which will also expand to produce thrust — just without the explosive chemical reaction. If that intrigues you, then take a look at this compressed air launchpad for paper rockets by Aiden Wyandt.
Compressed air can be dangerous, too. But 80 PSI (the highest tested pressure for this project) doesn’t pose a huge risk with proper hardware. The downside is that all of the gas expansion is immediate and comes from the launcher. In that way, it is more like a cannon than a true rocket. This is perfect for cheap, handcrafted paper missiles and the launcher makes that both fun and safe.
Inside the laser-cut plywood enclosure is an Arduino UNO R4 WiFi board. It receives power from a 20V DeWalt tool battery boosted to 24V. That also powers solenoid valves through relays and the Arduino controls those, along with the LED lighting. The Arduino hosts a web interface for arming and launching, so the kids can move to a safe distance. Once the countdown completes, the solenoid will open and compressed air will expand into the launch tube to send the rocket flying.
That air comes from an external air compressor through a standard fitting. It goes into a pair of small tanks and the solenoids sit between those tanks and the launch tubes. Because there are two, this launcher can handle two rockets before needing to be reset.
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