{
 "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": "ross-yoke",
 "name": "Ross yoke a = h = 20 for two parallel syringes",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "What shape and size is a Ross yoke that gives 90° between two pistons?",
 "tags": [
  "ross yoke",
  "alpha",
  "linkage",
  "syringe",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "ross yoke dimensions",
  "ross yoke stl",
  "ross yoke 90 degree",
  "ross yoke alpha stirling"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/ross-yoke/",
 "sheet_txt": "https://xemstudio.com/objects/ross-yoke/sheet.txt",
 "sheet": {
  "basis": "Linkage solved over a full turn (720 steps) in the generator: crank e 6, yoke a = h = 20, rocking link 40 from a pivot at (−40, 20), con-rods 60",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The triangular rocker of the Ross yoke alpha. Its half-width equals its height (a = h = 20), which puts the two top corners a quarter-turn apart: piston phase 90.0°, strokes 17.0 and 17.2 mm.",
   "Bottom vertex: a Ø3 hole (fit: run) that rides on the crank pin. Top corners at ±20: Ø3 holes (fit: press) for the con-rod pins. Between them, the top-middle Ø3 hole (press) for the rocking-link pin.",
   "Outline 52 × 32 × 6 with 3 mm corner radii."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "a (half-width)",
     20
    ],
    [
     "h (height)",
     20
    ],
    [
     "outline",
     "52 × 32 × 6"
    ],
    [
     "crank-pin hole",
     "Ø3 run"
    ],
    [
     "con-rod and rocking pins",
     "3 × Ø3 press"
    ],
    [
     "phase",
     "90.0°"
    ],
    [
     "strokes",
     "17.0 / 17.2"
    ],
    [
     "max con-rod angle",
     "0.91°"
    ]
   ]
  }
 },
 "sheet_text": "Ross yoke a = h = 20 for two parallel syringes — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/ross-yoke/  (CC BY 4.0)\nBasis: Linkage solved over a full turn (720 steps) in the generator: crank e 6, yoke a = h = 20, rocking link 40 from a pivot at (−40, 20), con-rods 60\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The triangular rocker of the Ross yoke alpha. Its half-width equals its height (a = h = 20), which puts the two top corners a quarter-turn apart: piston phase 90.0°, strokes 17.0 and 17.2 mm.\n- Bottom vertex: a Ø3 hole (fit: run) that rides on the crank pin. Top corners at ±20: Ø3 holes (fit: press) for the con-rod pins. Between them, the top-middle Ø3 hole (press) for the rocking-link pin.\n- Outline 52 × 32 × 6 with 3 mm corner radii.\n\nparameter  value\na (half-width)  20\nh (height)  20\noutline  52 × 32 × 6\ncrank-pin hole  Ø3 run\ncon-rod and rocking pins  3 × Ø3 press\nphase  90.0°\nstrokes  17.0 / 17.2\nmax con-rod angle  0.91°\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Ross yoke — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Ross_yoke\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, 1 parts): https://xemstudio.com/files/hardware/ross-yoke/index.json\nAPI: https://xemstudio.com/api/geometry?object=ross-yoke\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Ross yoke",
   "url": "https://en.wikipedia.org/wiki/Ross_yoke",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "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": [
  "ross-yoke-frame",
  "ross-rocking-link",
  "ross-crank-disc",
  "pin-end-con-rods",
  "list-ross-yoke-alpha"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "ross-crank-disc",
     "why": "bottom vertex rides the disc's Ø3 crank pin"
    },
    {
     "slug": "pin-end-con-rods",
     "why": "conrod-60 on the ±20 corner pins"
    },
    {
     "slug": "ross-rocking-link",
     "why": "top-middle pin to the rocking link"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "stirling-crankshafts",
     "why": "Ø3 × 12 and Ø3 × 20 pins, spacers"
    },
    {
     "slug": "metric-shafts",
     "why": "3 mm collars on the free pin ends"
    }
   ]
  }
 ],
 "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": "yoke corner and top pins",
   "exact": "Ø3",
   "mates": "Ø3 pins",
   "fit": "press",
   "files": "ross-yoke-"
  },
  {
   "feature": "yoke crank-pin hole",
   "exact": "Ø3",
   "mates": "crank pin (turns in it)",
   "fit": "run",
   "files": "ross-yoke-"
  }
 ],
 "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 gives 90° on a Ross yoke?",
   "a": "Half-width equal to height, a = h. Here a = h = 20 with a 6 mm crank and 40 mm rocking link gives 90.0°, checked over a full turn."
  },
  {
   "q": "Why are Ross yoke con-rods almost vertical?",
   "a": "The yoke's top corners move nearly straight up and down; the 60 mm rods stay within 0.91° of vertical, so the pistons see almost no side load."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "ross-yoke-a20-h20",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ross-yoke-kit/ross-yoke-a20-h20.step",
   "stl": "https://xemstudio.com/files/hardware/ross-yoke-kit/ross-yoke-a20-h20.stl",
   "note": "Ross yoke a = h = 20: Ø3 running hole on the crank pin at the bottom vertex, Ø3 press holes for the two con-rod pins at ±20 and the rocking pin between them"
  }
 ],
 "markdown": "https://xemstudio.com/objects/ross-yoke/index.md"
}