Epicyclic (planetary) gear train: sun 24, planets 18, ring 60 — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/epicyclic-gear-train-mechanism/  (CC BY 4.0)
Basis: Xem Studio design following Brown No. 502 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A sun gear, three planets on a carrier and a ring gear: hold the ring and drive the sun, and the carrier turns at 1/(1 + N_ring/N_sun) = 24/84 of sun speed (3.5 : 1) in the same direction.
- Tooth counts satisfy N_ring = N_sun + 2·N_planet (60 = 24 + 36) and (N_sun + N_ring)/planets = 84/3 = 28 (whole), so three equally spaced planets mesh with both at once — checked here at the drawn pose.
- Hold the carrier instead and the ring turns backwards at 24/60; hold the sun and ring-to-carrier is 60/84. Brown's Nos. 502–507 are the epicyclic trains.
- Parts (each has its own page): internal-ring-gear-m1-60t, spur-gears-module-1, planet-carrier-3x-r21, dowel-pins-metric.
- Brown's movement No. 502 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
sun  24 T (Ø8 bore)
planets  3 × 18 T on Ø5 dowels
ring  60 T internal
carrier radius  21 mm
ratio, ring fixed  3.5 : 1 sun to carrier

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. 502: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_502.html

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/epicyclic-gear-train-mechanism/index.json
API: https://xemstudio.com/api/geometry?object=epicyclic-gear-train-mechanism