This remarkable bit of gearing has appeared on HowStuffWorks right before. You might realize it from the electric screwdriver write-up. An automatic transmission has two entire planetary gearsets folded alongside one another into a person part. See How Gear Ratios Work for an introduction to planetary gearsets. You may enjoy https://gearbox-auto08517.blogdanica.com/34105002/gearbox-auto-no-further-a-mystery