One pinion driving an internal and a spur gear on one axis (two speeds) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/pinion-driving-internal-and-spur-gear-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 55 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A pinion sits between a ring gear and a spur gear that share an axis: it drives the ring the same way at 20/60 of its speed and the spur gear the opposite way at 20/20 — two speeds and two directions from one pinion.
- The tooth counts must satisfy N_ring = N_spur + 2·N_pinion (60 = 20 + 2 × 20) so both meshes sit at the same 20 mm centre distance.
- It is the fixed-carrier (star) form of an epicyclic train; Brown's No. 55 draws it with the two driven gears on one shaft.
- Parts (each has its own page): internal-ring-gear-m1-60t, spur-gears-module-1.
- Brown's movement No. 55 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
ring  60 T internal
spur gear  20 T
pinion  20 T
centre distance  20 mm
speeds (pinion = 1)  ring 1/3 same way; spur 1 opposite

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala
- 507movements.com: Brown's movement No. 55: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_055.html

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/pinion-driving-internal-and-spur-gear-mechanism/index.json
API: https://xemstudio.com/api/geometry?object=pinion-driving-internal-and-spur-gear-mechanism