The cannon looks to me like the kind that uses calcium carbide. As a kid, I had one that looked like that. It came with powdered calcium carbide that you put in a chamber at the top. The cannon had some water and when you depressed a button, a small measured amount of carbide fell into the water producing a combustible gas that was ignited with a sparker thingy - produced an impressive boom!
I agree with you about being active. I too play the piano:
I got into the multicopter hobby because I wanted to learn about how they worked and wanted to learn to fly them. I have documented my experiences - trials, failures, successes, etc. on YouTube as well. I would like to go to school and study math, probability and statistics. Since I'm retired, I have been focused on investing and have learned about trading options. I also swim and ride bicycles to keep fit - so many things to do and they all beat working!