When it comes to 7 speed hub gears that are available in the current market, there are two approaches to implementation: First, the single stage approach, with compound planet gears having 3 different radii. This type of 7 speed implementation can be found in hubs produced by Sturmey Archer, and by Sachs, since the mid 1990’s.
Very briefly, they achieve 7 speeds by gearing up and gearing down through the same planetary gear set, ie increase gears are achieved by driving the planet cage (hub is driven by the ring gear) and reduction is achieved by driving the ring gear (planet cage drives the hub shell). 3 reduction gears (as the planet pinions have 3 steps) + 3 increase gears + direct drive = 7 speeds. Note that this design is kind of like an extension of the Sturmey Archer 5 speed: essentially an S5 with an extra sun pinion and with 3 stepped planet pinions instead of the two-stepped planets in the S5.
Option 2 is more interesting. Continue reading “Shimano Inter 7/Nexus 7 disassembly”