Right-left arrow keys rotate the small gear (15 or 30 teeth). Up-down arrow keys rotate the large gear (60 teeth). Space moves the small gear inside or outside the large gear. Press 1 for 30-tooth small gear; press 2 for 15-tooth small gear. C changes the backdrop color. T activates the "tracker," which highlights one tooth on the small gear. (This is the only element not made with the pen).
I was just playing around with drawing gear shapes, but I've since learned that this project encompasses two math ideas - the "Tusi couple" and the "coin rotation paradox" - which you can read more about here, if you're interested: https://en.wikipedia.org/wiki/Tusi_couple https://en.wikipedia.org/wiki/Coin_rotation_paradox Here's my function for drawing gears with different properties: https://scratch.mit.edu/projects/104740309/
