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A stepped planet series gear looks like this:

enter image description here

Given that:

  • Planet gears are evenly distributed (with 120°)
  • Sun-gear-1 and Sun-gear-2 is lined up.
  • Sun gear tooth counts: nS1, nS2
  • Planet gear tooth counts: nFGS (first gear step), nSGS (second gear step)
  • Ring gear tooth count: nR1
  • Ring gear belongs to Sun-gear-1 and FGS
  • One tooth of FGS and one tooth of SGS is lined up (on the same line to the center) and marked with M.
  • FGS of Planet-gear-1 is touching the Ring at Mth tooth.

In order to assemble this gearbox:

  • Make M point of first-gear-step of Planet-gear-1 touch the Ring at Ring-tooth-0.
  • Make M point of first-gear-step of Planet-gear-2 touch the Ring at Ring-tooth-x.
  • Make M point of first-gear-step of Planet-gear-3 touch the Ring at Ring-tooth-y.
  • Roll the Planet-gear-2 to R1/3th tooth of the Ring.
  • Roll the Planet-gear-3 to R1*2/3th tooth of the Ring.

In this procedure, how do we calculate x and y values?

Example Case

Taken from http://tricolour.net/rohloff.html

I realized I needed to turn each index tooth by 2/3 of a tooth to get it to mesh.

enter image description here

Index tooth (M point) of the gears are marked with a black dot in the picture.

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  • $\begingroup$ Maybe something is being lost in translation, but shouldn't x and y just be R1/3 and 2*R1/3 since the planets are equally spaced? $\endgroup$
    – jko
    Sep 9 '20 at 11:38
  • $\begingroup$ @jko No. I added the example case, please see my edit. $\endgroup$
    – ceremcem
    Sep 10 '20 at 5:21

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