{
 "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": "linear-alternator-mover",
 "name": "Linear alternator mover: Ø35 carrier for 16 Ø10 × 3 magnets",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "What does the moving magnet part of a linear alternator look like and what size is it?",
 "tags": [
  "linear alternator",
  "moving magnet",
  "free piston",
  "mover",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "linear alternator mover",
  "moving magnet linear generator",
  "magnet carrier stl",
  "free piston alternator magnets"
 ],
 "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/linear-alternator-mover/",
 "sheet_txt": "https://xemstudio.com/objects/linear-alternator-mover/sheet.txt",
 "sheet": {
  "basis": "Moving-magnet layout as in Sunpower / NASA convertors; pockets at the Ø10 × 3 disc magnet; checked in the generator (alt_check)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The moving part of the linear alternator: a Ø35 × 26 carrier on a Ø12 × 6 hub, 32 mm overall, with a Ø5 bore (fit: slide) and a Ø2.5 radial hole (M3 tap size) in the hub for a grub screw.",
   "Two axial rows of 8 pockets (fit: press) for Ø10 × 3 disc magnets, faces out, 12 mm apart along the axis, the second row turned half a pocket. Row 1 all north out, row 2 all south out: the flux through each coil reverses as the mover passes.",
   "With magnets it is about 58 g, which adds to the piston's moving mass. It clamps the 5 mm piston tube or a Ø5 rod and sits centred in the coils at mid-stroke, 1.0 mm from the bobbin bore."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "carrier",
     "Ø35 × 26"
    ],
    [
     "hub",
     "Ø12 × 6"
    ],
    [
     "bore",
     "Ø5"
    ],
    [
     "magnet pockets",
     "2 rows × 8, Ø10 × 3"
    ],
    [
     "row pitch",
     12
    ],
    [
     "air gap to bobbin",
     1
    ],
    [
     "mass with magnets",
     "≈ 58 g"
    ]
   ]
  }
 },
 "sheet_text": "Linear alternator mover: Ø35 carrier for 16 Ø10 × 3 magnets — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/linear-alternator-mover/  (CC BY 4.0)\nBasis: Moving-magnet layout as in Sunpower / NASA convertors; pockets at the Ø10 × 3 disc magnet; checked in the generator (alt_check)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The moving part of the linear alternator: a Ø35 × 26 carrier on a Ø12 × 6 hub, 32 mm overall, with a Ø5 bore (fit: slide) and a Ø2.5 radial hole (M3 tap size) in the hub for a grub screw.\n- Two axial rows of 8 pockets (fit: press) for Ø10 × 3 disc magnets, faces out, 12 mm apart along the axis, the second row turned half a pocket. Row 1 all north out, row 2 all south out: the flux through each coil reverses as the mover passes.\n- With magnets it is about 58 g, which adds to the piston's moving mass. It clamps the 5 mm piston tube or a Ø5 rod and sits centred in the coils at mid-stroke, 1.0 mm from the bobbin bore.\n\nparameter  value\ncarrier  Ø35 × 26\nhub  Ø12 × 6\nbore  Ø5\nmagnet pockets  2 rows × 8, Ø10 × 3\nrow pitch  12\nair gap to bobbin  1.0\nmass with magnets  ≈ 58 g\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- NASA (NTRS, public domain): Linear alternator design for free-piston Stirling convertors (2005) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20050182934\n- NASA (NTRS, public domain): Sunpower/NASA 80 We free-piston Stirling convertor (2002) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20020047256\n- Wikipedia: Linear alternator — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Linear_alternator\n- Wikipedia: Free-piston engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Free-piston_engine\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/linear-alternator-mover/index.json\nAPI: https://xemstudio.com/api/geometry?object=linear-alternator-mover\n",
 "sources": [
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Linear alternator design for free-piston Stirling convertors (2005)",
   "url": "https://ntrs.nasa.gov/search?q=20050182934",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Sunpower/NASA 80 We free-piston Stirling convertor (2002)",
   "url": "https://ntrs.nasa.gov/search?q=20020047256",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Linear alternator",
   "url": "https://en.wikipedia.org/wiki/Linear_alternator",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Free-piston engine",
   "url": "https://en.wikipedia.org/wiki/Free-piston_engine",
   "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": [
  "linear-alternator-bobbin",
  "linear-alternator-housing",
  "neodymium-disc-magnets",
  "e-clip-grooved-rods-5mm",
  "tri-clamp-flexure-head",
  "list-free-piston-2in"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "linear-alternator-bobbin",
     "why": "runs inside the Ø37 bore, 1.0 mm gap"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "e-clip-grooved-rods-5mm",
     "why": "clamps the Ø5 rod"
    },
    {
     "slug": "tri-clamp-flexure-head",
     "why": "clamps the 5 mm piston tube"
    },
    {
     "slug": "spiral-flexure-bearing",
     "why": "flexures keep it centred in the gap"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "neodymium-disc-magnets",
     "why": "16 × Ø10 × 3 in the pockets"
    },
    {
     "slug": "set-screws-metric",
     "why": "M3 grub in the hub"
    }
   ]
  }
 ],
 "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": "mover bore",
   "exact": "Ø5",
   "mates": "5 mm tube or Ø5 rod (M3 grub)",
   "fit": "slide",
   "files": "alt-mover-"
  },
  {
   "feature": "magnet pockets",
   "exact": "Ø10 × 3",
   "mates": "Ø10 × 3 disc magnet",
   "fit": "press",
   "files": "alt-mover-"
  },
  {
   "feature": "mover grub hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "alt-mover-"
  }
 ],
 "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": "Why two rows of magnets on a linear alternator mover?",
   "a": "Each coil must see the flux reverse as the mover passes; two rows of opposite polarity under two oppositely wound coils do that."
  },
  {
   "q": "What magnets go in the mover?",
   "a": "Sixteen Ø10 × 3 disc magnets, eight per row, faces out."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "alt-mover-35-2x8-10x3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-kit/alt-mover-35-2x8-10x3.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-kit/alt-mover-35-2x8-10x3.stl",
   "note": "mover: Ø35 × 26 carrier with 2 axial rows of 8 Ø10 × 3 magnet pockets (faces out; row 1 all N out, row 2 all S out, rows offset half a pocket), 12 mm pitch, Ø5 bore, Ø12 hub with an M3 grub: clamps the 5 mm piston tube or a Ø5 rod"
  }
 ],
 "markdown": "https://xemstudio.com/objects/linear-alternator-mover/index.md"
}