An in depth look at the design and function of the classic Sturmey Archer 3 speed.
here is a link to to the NIG update.
https://www.youtube.com/watch?v=-UyHVWsvzQs
For another great write up with graphics and detailed explanations, check this out.
https://josephgunnwriting.wordpress.com/deep-dive-into-the-internal-workings-of-a-three-speed-bicycle-hub/