I used an Instructables project to build a harmonograph, which produces beautiful art using gravity and motion.
Right away I was able to create some interesting patterns.
The drawing arm that I made had too much lateral wobble. I later learned I need a universal drill stand, but I compensated for the messy hole by using 3D printed brackets to secure the arm and eliminate the wobble.
Immediately I was able to achieve much more clear and detailed designs. I used both a two pound weight as well as a two and five pound weight together.
This is another great low-tech project that allows for interesting explorations and resulting art. Build one yourself!