This wonderful bit of gearing has appeared on HowStuffWorks right before. You might recognize it from the electric screwdriver write-up. An automatic transmission is made up of two entire planetary gearsets folded with each other into a single ingredient. See How Equipment Ratios Work for an introduction to planetary gearsets. https://kylertxvvq.jts-blog.com/33119851/new-step-by-step-map-for-gearbox-auto