{
 "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": "round-belt-generator-drive",
 "name": "Round-belt generator drive: Ø84 crank pulley, 2208 generator pulley, Ø5 belts",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Stirling & thermoacoustic",
 "year": null,
 "question": "How do I belt a small generator off a Stirling engine's crank?",
 "tags": [
  "pulley",
  "belt",
  "generator",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "round belt pulley",
  "stirling generator belt drive"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 4,
 "url": "https://xemstudio.com/objects/round-belt-generator-drive/",
 "sheet_txt": "https://xemstudio.com/objects/round-belt-generator-drive/sheet.txt",
 "sheet": {
  "basis": "Design values; 2208 rotor-top hole pattern from the gimbal-motor envelope on this site",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A Ø5 round belt from an Ø84 crank pulley (pitch Ø80) to an Ø16 pulley (pitch Ø13.33) bolted to a 2208 gimbal motor's rotor top: 6 : 1, so 600 rpm at the crank is 3600 rpm at the generator.",
   "Belt lengths on the centre line: 339.1 mm at 90 centres (horizontal gamma), 415.2 mm at 130 (walking-beam gamma). Round belts are cut to length and joined; tension by stretch.",
   "The belt and pulleys turn the crank's shaft power into motor speed; the electrical output on each engine's page comes from the motor's published KV and resistance."
  ],
  "table": {
   "columns": [
    "part",
    "size"
   ],
   "rows": [
    [
     "crank-pulley-84-b8",
     "Ø84 × 6, pitch Ø80, hub Ø20"
    ],
    [
     "generator-pulley-2208-pd13.33",
     "Ø16 × 8, pitch Ø13.33"
    ],
    [
     "round-belt-5-c90",
     "Ø5 × 339.1"
    ],
    [
     "round-belt-5-c130",
     "Ø5 × 415.2"
    ]
   ]
  }
 },
 "sheet_text": "Round-belt generator drive: Ø84 crank pulley, 2208 generator pulley, Ø5 belts — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/round-belt-generator-drive/  (CC BY 4.0)\nBasis: Design values; 2208 rotor-top hole pattern from the gimbal-motor envelope on this site\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A Ø5 round belt from an Ø84 crank pulley (pitch Ø80) to an Ø16 pulley (pitch Ø13.33) bolted to a 2208 gimbal motor's rotor top: 6 : 1, so 600 rpm at the crank is 3600 rpm at the generator.\n- Belt lengths on the centre line: 339.1 mm at 90 centres (horizontal gamma), 415.2 mm at 130 (walking-beam gamma). Round belts are cut to length and joined; tension by stretch.\n- The belt and pulleys turn the crank's shaft power into motor speed; the electrical output on each engine's page comes from the motor's published KV and resistance.\n\npart  size\ncrank-pulley-84-b8  Ø84 × 6, pitch Ø80, hub Ø20\ngenerator-pulley-2208-pd13.33  Ø16 × 8, pitch Ø13.33\nround-belt-5-c90  Ø5 × 339.1\nround-belt-5-c130  Ø5 × 415.2\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/round-belt-generator-drive/index.json\nAPI: https://xemstudio.com/api/geometry?object=round-belt-generator-drive\n",
 "sources": [
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "gimbal-motor-2208-envelope",
  "list-tri-clamp-horizontal-gamma",
  "list-tri-clamp-walking-beam-gamma"
 ],
 "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": [
  {
   "feature": "crank pulley bore",
   "exact": "Ø8",
   "mates": "Ø8 crank shaft (M4 grub)",
   "fit": "slide",
   "files": "crank-pulley"
  },
  {
   "feature": "grooves",
   "exact": "Ø5 round, pitch Ø80 / Ø13.33",
   "mates": "Ø5 round belt",
   "fit": "designed",
   "files": "all"
  },
  {
   "feature": "pulley flange holes",
   "exact": "4 × Ø2.4 on 12 × 12",
   "mates": "M2 screws into the 2208 rotor top",
   "fit": "designed",
   "files": "generator-pulley"
  }
 ],
 "fit_classes": {
  "press": "stays put: pin, tube, bearing or magnet held by interference. Typical FDM: hole +0.0 to +0.1 mm on diameter.",
  "slide": "assembles by hand and is held by a grub, pinch or clamp: shaft in a hub, rod in a socket, spigot in a bore. Typical FDM: +0.2 mm.",
  "run": "turns or slides in use: pin in a link, rod through a guide. Typical FDM: +0.3 mm.",
  "socket": "large sliding fit: syringe barrel, sleeve, bobbin in a bore. Typical FDM: +0.3 mm.",
  "clamp": "split part that closes on the mating part with screws: make it at size.",
  "designed": "a gap that is part of the design (piston fit option, displacer gap, air gap): do not change."
 },
 "faq": [
  {
   "q": "What ratio?",
   "a": "6 : 1: the 2208's KV 128 then gives about 28 V open circuit at 600 rpm at the crank."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "crank-pulley-84-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/round-belt-generator-drive/crank-pulley-84-b8.step",
   "stl": "https://xemstudio.com/files/hardware/round-belt-generator-drive/crank-pulley-84-b8.stl",
   "note": "crank pulley Ø84 × 6 with a Ø5 round-belt groove on pitch Ø80, hub Ø20 × 19.5, Ø8 bore, M4 tapped hub hole"
  },
  {
   "file": "generator-pulley-2208-pd13.33",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/round-belt-generator-drive/generator-pulley-2208-pd13.33.step",
   "stl": "https://xemstudio.com/files/hardware/round-belt-generator-drive/generator-pulley-2208-pd13.33.stl",
   "note": "generator pulley for a 2208 rotor top: flange Ø24 × 3 with 4 × Ø2.4 (12 × 12), neck Ø8, pulley Ø16 × 8 with a Ø5 groove on pitch Ø13.33"
  },
  {
   "file": "round-belt-5-c90",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/round-belt-generator-drive/round-belt-5-c90.step",
   "stl": "https://xemstudio.com/files/hardware/round-belt-generator-drive/round-belt-5-c90.stl",
   "note": "Ø5 round belt on pitch circles Ø80 and Ø13.33 at 90 centres: 339.1 mm long on its centre line"
  },
  {
   "file": "round-belt-5-c130",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/round-belt-generator-drive/round-belt-5-c130.step",
   "stl": "https://xemstudio.com/files/hardware/round-belt-generator-drive/round-belt-5-c130.stl",
   "note": "Ø5 round belt on pitch circles Ø80 and Ø13.33 at 130 centres: 415.2 mm long on its centre line"
  }
 ],
 "markdown": "https://xemstudio.com/objects/round-belt-generator-drive/index.md"
}