Model rockets are a nerdy hobby that can combine aerodynamics,
electronics, radio technology, computer simulation, photography, art,
composite materials and freezing your ass off in winter. Mixing your
own propellants is not required nowadays, so it is also relatively
safe. I have built many small models that fly on A...D motors, and
have contributed to SATS's and
Pollux's joint Haisunäätä
projects, which used J and L class hybrid engines.
I have been responsible for experimental avionics, control
electronics, onboard cameras, data logging and radio beacons.
Here's some stuff and more photos: