{
 "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-kit",
 "name": "Ross yoke kit (alpha Stirling with parallel cylinders)",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "What is a Ross yoke and how do I make an alpha Stirling engine with parallel cylinders?",
 "tags": [
  "ross yoke",
  "alpha",
  "mechanism",
  "linkage",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "ross yoke stirling",
  "ross yoke mechanism",
  "alpha stirling parallel cylinders",
  "andy ross yoke",
  "ross yoke 3d print"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 6,
 "url": "https://xemstudio.com/objects/ross-yoke-kit/",
 "sheet_txt": "https://xemstudio.com/objects/ross-yoke-kit/sheet.txt",
 "sheet": {
  "basis": "Andy Ross's yoke (1970s): a triangular rocker on a single crank gives two parallel pistons ~90° apart with near-straight-line motion; proportions a = 30, h = 20 for 16 mm strokes",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Alpha engines need two pistons 90° out of phase; the usual V-twin crank puts the cylinders at 90°. The Ross yoke lets both cylinders sit side by side and parallel: a triangular rocker pivots on a short rocking link, its bottom corner rides the crank pin, and its two top corners drive the pistons through short con-rods. The geometry makes each piston's motion almost straight (low side load) and roughly 90° apart.",
   "Proportions: top pivots at ±a, crank pivot at −h below, rocking pivot near the centroid; a/h ≈ 1.5, crank throw ≈ h/2.5. With a 30 / h 20 / e 8 the strokes are ~16 mm and phase ~90°. Cylinder spacing = 2a = 60 mm... here the syringe block uses 34 mm spacing with the a = 30 yoke angled; use a = 17 for a dead-parallel block, or the 2× syringe block as the compact version.",
   "Parts: yoke, rocking link (frame to yoke centroid, 623 bearing), two con-rods, crank disc, cylinder block for two 10 mL syringes (the simplest alpha: one hot, one cold, a tube between), flywheel from the crank kit.",
   "LES: the alpha demonstrator with two syringes; the hot syringe sits in a tri-clamp hot end via the power head."
  ],
  "table": {
   "columns": [
    "part",
    "size",
    "note"
   ],
   "rows": [
    [
     "yoke",
     "a 30, h 20 (or 40/25)",
     "623 at centroid"
    ],
    [
     "rocking link",
     30,
     "frame pivot"
    ],
    [
     "con-rods",
     "45 × 2",
     "Ø3 pins"
    ],
    [
     "crank",
     "e 8 (stroke 16)",
     "Ø5 shaft"
    ],
    [
     "cylinder block",
     "2 × 10 mL syringes @ 34",
     "alpha"
    ]
   ]
  }
 },
 "sheet_text": "Ross yoke kit (alpha Stirling with parallel cylinders) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/ross-yoke-kit/  (CC BY 4.0)\nBasis: Andy Ross's yoke (1970s): a triangular rocker on a single crank gives two parallel pistons ~90° apart with near-straight-line motion; proportions a = 30, h = 20 for 16 mm strokes\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Alpha engines need two pistons 90° out of phase; the usual V-twin crank puts the cylinders at 90°. The Ross yoke lets both cylinders sit side by side and parallel: a triangular rocker pivots on a short rocking link, its bottom corner rides the crank pin, and its two top corners drive the pistons through short con-rods. The geometry makes each piston's motion almost straight (low side load) and roughly 90° apart.\n- Proportions: top pivots at ±a, crank pivot at −h below, rocking pivot near the centroid; a/h ≈ 1.5, crank throw ≈ h/2.5. With a 30 / h 20 / e 8 the strokes are ~16 mm and phase ~90°. Cylinder spacing = 2a = 60 mm... here the syringe block uses 34 mm spacing with the a = 30 yoke angled; use a = 17 for a dead-parallel block, or the 2× syringe block as the compact version.\n- Parts: yoke, rocking link (frame to yoke centroid, 623 bearing), two con-rods, crank disc, cylinder block for two 10 mL syringes (the simplest alpha: one hot, one cold, a tube between), flywheel from the crank kit.\n- LES: the alpha demonstrator with two syringes; the hot syringe sits in a tri-clamp hot end via the power head.\n\npart  size  note\nyoke  a 30, h 20 (or 40/25)  623 at centroid\nrocking link  30  frame pivot\ncon-rods  45 × 2  Ø3 pins\ncrank  e 8 (stroke 16)  Ø5 shaft\ncylinder block  2 × 10 mL syringes @ 34  alpha\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine\n- Andy Ross: Making Stirling Engines (Ross yoke) — book — reference [verify license at link] — https://www.stirlingengine.com/\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, 6 parts): https://xemstudio.com/files/hardware/ross-yoke-kit/index.json\nAPI: https://xemstudio.com/api/geometry?object=ross-yoke-kit\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Stirling engine",
   "url": "https://en.wikipedia.org/wiki/Stirling_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Andy Ross",
   "title": "Making Stirling Engines (Ross yoke)",
   "url": "https://www.stirlingengine.com/",
   "formats": [
    "book"
   ],
   "license": "reference",
   "license_verified": false,
   "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": [
  "motion-mechanisms",
  "plastic-syringes",
  "crank-conrod-flywheel-kit",
  "ball-bearings-metric",
  "stirling-configurations-guide",
  "alpha-twin-crank-90"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "plastic-syringes",
     "why": "10 mL barrels in the cylinder block"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "syringe-pistons",
     "why": "conrod-45 into the piston fork"
    },
    {
     "slug": "crank-conrod-flywheel-kit",
     "why": "flywheel"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "alpha-twin-crank-90",
     "why": "V-twin alpha"
    },
    {
     "slug": "rhombic-drive-kit",
     "why": "balanced beta"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "ball-bearings-metric",
     "why": "623 at the rocking pivot"
    },
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 pins"
    }
   ]
  }
 ],
 "faq": [
  {
   "q": "What is a Ross yoke?",
   "a": "A triangular rocker on one crank that drives two parallel pistons about 90° apart with nearly straight-line motion: the way to build an alpha Stirling with side-by-side cylinders instead of a V."
  },
  {
   "q": "What phase angle does a Ross yoke give?",
   "a": "About 90° with a/h ≈ 1.5; it varies a few degrees through the cycle, which is harmless."
  },
  {
   "q": "Can I make an alpha Stirling from two syringes?",
   "a": "Yes: the cylinder block takes two 10 mL barrels; heat one, cool the other, connect them with a short tube and a regenerator plug, drive the plungers with the Ross yoke."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "ross-yoke-a30-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-a30-h20.step",
   "stl": "https://xemstudio.com/files/hardware/ross-yoke-kit/ross-yoke-a30-h20.stl",
   "note": "Ross yoke rocker: piston pivots ±30 mm, crank pivot 20 mm below, 623 pocket at the rocking pivot"
  },
  {
   "file": "ross-yoke-a40-h25",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ross-yoke-kit/ross-yoke-a40-h25.step",
   "stl": "https://xemstudio.com/files/hardware/ross-yoke-kit/ross-yoke-a40-h25.stl",
   "note": "larger rocker ±40 / 25"
  },
  {
   "file": "rocking-link-30",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ross-yoke-kit/rocking-link-30.step",
   "stl": "https://xemstudio.com/files/hardware/ross-yoke-kit/rocking-link-30.stl",
   "note": "rocking link 30 mm (yoke centroid to frame pivot)"
  },
  {
   "file": "conrod-45",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ross-yoke-kit/conrod-45.step",
   "stl": "https://xemstudio.com/files/hardware/ross-yoke-kit/conrod-45.stl",
   "note": "piston con-rod 45 mm, Ø3.2 ends (2 needed)"
  },
  {
   "file": "crank-disc-stroke16",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ross-yoke-kit/crank-disc-stroke16.step",
   "stl": "https://xemstudio.com/files/hardware/ross-yoke-kit/crank-disc-stroke16.stl",
   "note": "crank disc, pin at 8 mm"
  },
  {
   "file": "cylinder-block-2x-syringe-10ml",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/ross-yoke-kit/cylinder-block-2x-syringe-10ml.step",
   "stl": "https://xemstudio.com/files/hardware/ross-yoke-kit/cylinder-block-2x-syringe-10ml.stl",
   "note": "alpha cylinder block: two parallel 10 mL syringe barrel sockets (Ø16.05) 34 mm apart, pinch slot"
  }
 ],
 "markdown": "https://xemstudio.com/objects/ross-yoke-kit/index.md"
}