We'll be using Fusion 360 to design the tumbler. Fusion 360 is a great tool, even for beginners, to design any physical project before building it. By designing the tumbler before buying wood and other parts I was able to figure out exactly what I needed.
If you're new to Fusion 360, here's a great video by Noe Ruiz that gives an overview of the software.
To design the tumbler we will first need to know the dimensions of our compost container. The can I'm using is 27" high X 21.5" diameter.