{
 "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": "sun-and-planet-gear-mechanism",
 "name": "Sun-and-planet gear (Watt's crank substitute), 30 : 30",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Gears",
 "year": null,
 "question": "How does a sun-and-planet gear replace a crank?",
 "tags": [
  "mechanism",
  "gears",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "sun and planet gear",
  "watt sun and planet",
  "planetary crank",
  "engranaje sol y planeta",
  "Sonnen-und-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/sun-and-planet-gear-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/sun-and-planet-gear-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 39 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A planet gear fixed to the end of a rocking rod is held in mesh with a sun gear on the output shaft by a free arm: each to-and-fro cycle of the rod carries the planet once round the sun.",
   "With equal gears the sun makes two turns per cycle (1 + N_planet/N_sun), which is why it was used: twice the shaft speed of a plain crank.",
   "Brown's No. 39 is the arrangement used by Watt as a substitute for the crank. Module 1, 30 + 30 teeth, centre distance 30 mm.",
   "Parts (each has its own page): spur-gears-module-1, sun-and-planet-arm-30, sun-and-planet-rod-100, linear-shafts-h6.",
   "Brown's movement No. 39 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "sun / planet",
     "30 T / 30 T, module 1"
    ],
    [
     "arm centres",
     "30 mm"
    ],
    [
     "sun turns per rod cycle",
     "2"
    ],
    [
     "rod",
     "100 mm"
    ]
   ]
  }
 },
 "sheet_text": "Sun-and-planet gear (Watt's crank substitute), 30 : 30 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/sun-and-planet-gear-mechanism/  (CC BY 4.0)\nBasis: Xem Studio design following Brown No. 39 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A planet gear fixed to the end of a rocking rod is held in mesh with a sun gear on the output shaft by a free arm: each to-and-fro cycle of the rod carries the planet once round the sun.\n- With equal gears the sun makes two turns per cycle (1 + N_planet/N_sun), which is why it was used: twice the shaft speed of a plain crank.\n- Brown's No. 39 is the arrangement used by Watt as a substitute for the crank. Module 1, 30 + 30 teeth, centre distance 30 mm.\n- Parts (each has its own page): spur-gears-module-1, sun-and-planet-arm-30, sun-and-planet-rod-100, linear-shafts-h6.\n- Brown's movement No. 39 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\nsun / planet  30 T / 30 T, module 1\narm centres  30 mm\nsun turns per rod cycle  2\nrod  100 mm\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. 39: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_039.html\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/sun-and-planet-gear-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=sun-and-planet-gear-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. 39: figure, his text and an animation",
   "url": "https://507movements.com/mm_039.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": [
  "spur-gears-module-1",
  "sun-and-planet-arm-30",
  "sun-and-planet-rod-100",
  "linear-shafts-h6"
 ],
 "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 sun-and-planet gear replace a crank?",
   "a": "A planet gear fixed to the end of a rocking rod is held in mesh with a sun gear on the output shaft by a free arm: each to-and-fro cycle of the rod carries the planet once round the sun."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "sun-and-planet-gear-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/sun-and-planet-gear-mechanism/sun-and-planet-gear-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/sun-and-planet-gear-mechanism/sun-and-planet-gear-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/sun-and-planet-gear-mechanism/index.md"
}