DIY Model Rocket Launcher Electronics

with Seeed Xiao RP2040 MCU + Rust code

schematic diagram of model rocket launcher electronics

Model rocket launching is a well-organized and very fun activity, for example (https://www.cmass.org/) has regular launch events over the years.

In case you like to have more fun and DIY your own model rocket launcher, the launch platform can be built with PVC pipe components: https://www.youtube.com/watch?v=8a85ntmwbNU

To build the electronics part of it, here are a few tips:

• +12V portable battery can provide high enough current (around 2A DC current) to ignite the motor starter.
• toothless mini alligator clips are light enough to grab onto the leads of the motor starter
• relay needs to handle the large DC current without being melted together

A SEEED RP2040 Xiao MCU board (with enough GPIO pins) is used to perform three functions:

1. on/off relay switch with GPIO0
2. continuity check with GPIO2 and GPIO26 (analog in); Neopixel for information display
3. read ignition button press with GPIO4 and GPIO27 (analog in)

motor starter like these are like fuses (very low resistance), once ignited with large enough current, they disconnect.

But before connecting +12V through the relay switch to the motor starter, a small current can be used (GPIO2 3.3V and 1k pull-up) to check whether both ends of the motor starter are connected properly to the alligator clips. This is usually called out before count down as “rocket has continuity”.

The FSM in firmware only turns on the relay for 5 seconds, after ignition button press is detected. After which, the relay is switched off, until the whole system is powered down and powered back on again by flicking off/on the “arm switch”.

Another safety feature is to have an LED across the clips. In case relay contacts are welded together due to large currents, it will no longer be controlled by MCU GPIO0. As the relay becomes always-on, this LED will have +12V across it, and being lit up brightly. So it’s important to make sure that this LED is off, before flicking off the “arm switch” after a launch.

Here is a cardboard box implementation of the launch box.