{
 "version": "2026-10-20",
 "license": "Dimension sheets are written by Xem Studio from the cited sources and are free to use (CC BY 4.0, attribute 'Xem Studio'). Linked files belong to their publishers under the license shown; Xem Studio does not host them. 'license_verified: false' means the license shown is from memory or the publisher's page as last read and should be confirmed at the link before commercial use.",
 "slug": "epicyclic-gear-train-mechanism",
 "name": "Epicyclic (planetary) gear train: sun 24, planets 18, ring 60",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Gears",
 "year": null,
 "question": "How does a planetary gear train get its ratio?",
 "tags": [
  "mechanism",
  "gears",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "planetary gear",
  "epicyclic gear",
  "planetary gearbox",
  "sun planet ring gear",
  "tren de engranajes epicicloidal",
  "Planetengetriebe"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/epicyclic-gear-train-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/epicyclic-gear-train-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 502 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "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."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "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"
    ]
   ]
  }
 },
 "sheet_text": "Epicyclic (planetary) gear train: sun 24, planets 18, ring 60 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/epicyclic-gear-train-mechanism/  (CC BY 4.0)\nBasis: Xem Studio design following Brown No. 502 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- 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.\n- 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.\n- 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.\n- Parts (each has its own page): internal-ring-gear-m1-60t, spur-gears-module-1, planet-carrier-3x-r21, dowel-pins-metric.\n- Brown's movement No. 502 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\nsun  24 T (Ø8 bore)\nplanets  3 × 18 T on Ø5 dowels\nring  60 T internal\ncarrier radius  21 mm\nratio, ring fixed  3.5 : 1 sun to carrier\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- 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\n- 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\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/epicyclic-gear-train-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=epicyclic-gear-train-mechanism\n",
 "sources": [
  {
   "publisher": "Henry T. Brown (1868, public domain)",
   "title": "Five Hundred and Seven Mechanical Movements — scan on archive.org",
   "url": "https://archive.org/details/fivehundredseven00browiala",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "507movements.com",
   "title": "Brown's movement No. 502: figure, his text and an animation",
   "url": "https://507movements.com/mm_502.html",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "internal-ring-gear-m1-60t",
  "spur-gears-module-1",
  "planet-carrier-3x-r21",
  "dowel-pins-metric"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [],
 "faq": [
  {
   "q": "How does a planetary gear train get its ratio?",
   "a": "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."
  },
  {
   "q": "What is the ratio of a planetary gear with the ring fixed?",
   "a": "1 + N_ring/N_sun from sun to carrier: 1 + 60/24 = 3.5 here."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "epicyclic-gear-train-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/epicyclic-gear-train-mechanism/epicyclic-gear-train-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/epicyclic-gear-train-mechanism/epicyclic-gear-train-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/epicyclic-gear-train-mechanism/index.md"
}