{
 "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-module-mover-2in",
 "name": "Linear alternator module mover: Ø48 piston cup, 40-magnet carrier and tube rod, sprung on two leaves",
 "kind": "hardware",
 "category": "Electronics",
 "group": "Generators & alternators",
 "year": null,
 "question": "What moves inside the clamp-in linear alternator module?",
 "tags": [
  "piston",
  "mover",
  "magnets",
  "free piston",
  "linear alternator",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "linear alternator mover",
  "moving magnet piston",
  "free piston alternator mover",
  "clearance seal piston cup"
 ],
 "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/linear-alternator-module-mover-2in/",
 "sheet_txt": "https://xemstudio.com/objects/linear-alternator-module-mover-2in/sheet.txt",
 "sheet": {
  "basis": "Design values; moving mass from the CAD volumes at 7.9 g/cm³ (metal parts, assumed) and 7.5 g/cm³ (magnets, published), each leaf adding its hub and a third of its arms",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Three parts and the magnets: a piston cup whose Ø48.00 × 24 land is the clearance seal in the 42 mm bored spool; a Ø18 tube rod pressed into the cup's socket; a Ø47 × 56 magnet carrier pressed on the tube in the 3 in bored spool, with the 40 Ø12 × 3 disc magnets of the free-piston generator in four rows (S, N, N, S from face A), faces out.",
   "The tube rod carries the hubs of leaf 1 (between the two bored spools) and leaf 2 (between the 3 in spool and the 25.4 mm spool) on four Ø28 collars: the magnets sit between the two leaves, so the stator's side pull acts between its supports and the cup's land runs on the axis without touching.",
   "The carrier's body is the magnetic return between the magnet rows, so it must be magnetically soft; the cup and tube only have to be stiff. Moving mass of the standard build: 865 g (piston cup 184, magnet carrier 428, tube rod 86, magnets (40) 102, collars (4) 56, grub screws (4) 1, leaves 1, 2 (share) 7 g).",
   "The cup is open toward face B: its inside is part of the bounce space. Its crown has three M3 tapped holes for the add-on mass discs (tuning page). At mid-stroke the crown face is 9.00 mm inside face A: a depth gauge on the crown is the module's centring check.",
   "The same mover serves both versions of the module. Only the tube rod differs: 108.15 long in the closed module (leaves 77.9 apart in the spool joints), 151.70 in the open frame (leaves 93.0 apart on the frame's seats)."
  ],
  "table": {
   "columns": [
    "part",
    "size"
   ],
   "rows": [
    [
     "la-piston-cup-48x24",
     "Ø48.00 × 24 land, crown 5"
    ],
    [
     "la-magnet-carrier-47x56",
     "Ø47 × 56, 40 pockets Ø12 × 3"
    ],
    [
     "la-tube-rod-18x14x108.15",
     "Ø18 / Ø14 × 108.15 (closed)"
    ],
    [
     "la-tube-rod-18x14x151.70",
     "Ø18 / Ø14 × 151.70 (open frame)"
    ],
    [
     "magnets",
     "40 × Ø12 × 3, rows S N N S at 14 pitch"
    ],
    [
     "moving mass",
     "865 g closed, 899 g open frame (standard build)"
    ]
   ]
  }
 },
 "sheet_text": "Linear alternator module mover: Ø48 piston cup, 40-magnet carrier and tube rod, sprung on two leaves — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/linear-alternator-module-mover-2in/  (CC BY 4.0)\nBasis: Design values; moving mass from the CAD volumes at 7.9 g/cm³ (metal parts, assumed) and 7.5 g/cm³ (magnets, published), each leaf adding its hub and a third of its arms\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Three parts and the magnets: a piston cup whose Ø48.00 × 24 land is the clearance seal in the 42 mm bored spool; a Ø18 tube rod pressed into the cup's socket; a Ø47 × 56 magnet carrier pressed on the tube in the 3 in bored spool, with the 40 Ø12 × 3 disc magnets of the free-piston generator in four rows (S, N, N, S from face A), faces out.\n- The tube rod carries the hubs of leaf 1 (between the two bored spools) and leaf 2 (between the 3 in spool and the 25.4 mm spool) on four Ø28 collars: the magnets sit between the two leaves, so the stator's side pull acts between its supports and the cup's land runs on the axis without touching.\n- The carrier's body is the magnetic return between the magnet rows, so it must be magnetically soft; the cup and tube only have to be stiff. Moving mass of the standard build: 865 g (piston cup 184, magnet carrier 428, tube rod 86, magnets (40) 102, collars (4) 56, grub screws (4) 1, leaves 1, 2 (share) 7 g).\n- The cup is open toward face B: its inside is part of the bounce space. Its crown has three M3 tapped holes for the add-on mass discs (tuning page). At mid-stroke the crown face is 9.00 mm inside face A: a depth gauge on the crown is the module's centring check.\n- The same mover serves both versions of the module. Only the tube rod differs: 108.15 long in the closed module (leaves 77.9 apart in the spool joints), 151.70 in the open frame (leaves 93.0 apart on the frame's seats).\n\npart  size\nla-piston-cup-48x24  Ø48.00 × 24 land, crown 5\nla-magnet-carrier-47x56  Ø47 × 56, 40 pockets Ø12 × 3\nla-tube-rod-18x14x108.15  Ø18 / Ø14 × 108.15 (closed)\nla-tube-rod-18x14x151.70  Ø18 / Ø14 × 151.70 (open frame)\nmagnets  40 × Ø12 × 3, rows S N N S at 14 pitch\nmoving mass  865 g closed, 899 g open frame (standard build)\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- K&J Magnetics: Neodymium magnet specifications: N42 Br 1.30–1.32 T, density 7.4–7.5 g/cm³ — web — maker page; values are facts [verify license at link] — https://www.kjmagnetics.com/specs.asp\n- Xem Studio: tools/gen_la_module.py: the module's geometry, masses, bounce volume, natural frequencies and every number on these pages — code — CC BY 4.0 — https://xemstudio.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, 4 parts): https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/index.json\nAPI: https://xemstudio.com/api/geometry?object=linear-alternator-module-mover-2in\n",
 "sources": [
  {
   "publisher": "K&J Magnetics",
   "title": "Neodymium magnet specifications: N42 Br 1.30–1.32 T, density 7.4–7.5 g/cm³",
   "url": "https://www.kjmagnetics.com/specs.asp",
   "formats": [
    "web"
   ],
   "license": "maker page; values are facts",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Xem Studio",
   "title": "tools/gen_la_module.py: the module's geometry, masses, bounce volume, natural frequencies and every number on these pages",
   "url": "https://xemstudio.com/",
   "formats": [
    "code"
   ],
   "license": "CC BY 4.0",
   "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-module-spools-2in",
  "linear-alternator-module-tuning-2in",
  "linear-alternator-module-open-frame-2in",
  "fpse-linear-alternator-stator",
  "tri-clamp-flexure-leaf",
  "fpse-hub-collars",
  "neodymium-disc-magnets",
  "linear-alternator-module-2in-datasheet",
  "list-linear-alternator-module-2in-closed",
  "list-linear-alternator-module-2in-open"
 ],
 "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": "land",
   "exact": "Ø48.00 × 24",
   "mates": "42 mm spool bore Ø48.00 (clearance seal)",
   "fit": "run",
   "files": "la-piston-cup"
  },
  {
   "feature": "socket",
   "exact": "Ø18 × 15",
   "mates": "tube rod end",
   "fit": "press",
   "files": "la-piston-cup"
  },
  {
   "feature": "hub boss",
   "exact": "Ø26",
   "mates": "mass disc bores",
   "fit": "slide",
   "files": "la-piston-cup"
  },
  {
   "feature": "skirt bore",
   "exact": "Ø42",
   "mates": "mass discs Ø41 (0.5 radial gap, no contact)",
   "fit": "designed",
   "files": "la-piston-cup"
  },
  {
   "feature": "tapped holes",
   "exact": "3 × Ø2.5 × 4 on r 17",
   "mates": "M3 mass-disc screws (M3 tap drill)",
   "fit": "designed",
   "files": "la-piston-cup"
  },
  {
   "feature": "OD",
   "exact": "Ø47.0",
   "mates": "3 in bored spool Ø48.00 (0.5 radial gap, no contact)",
   "fit": "designed",
   "files": "la-magnet-carrier"
  },
  {
   "feature": "bore",
   "exact": "Ø18 × 56",
   "mates": "tube rod",
   "fit": "press",
   "files": "la-magnet-carrier"
  },
  {
   "feature": "magnet pockets",
   "exact": "40 × Ø12 × 3 radial",
   "mates": "Ø12 × 3 disc magnets",
   "fit": "press",
   "files": "la-magnet-carrier"
  },
  {
   "feature": "vents",
   "exact": "8 × Ø2.5",
   "mates": "gas passage (no contact)",
   "fit": "designed",
   "files": "la-magnet-carrier"
  },
  {
   "feature": "OD",
   "exact": "Ø18",
   "mates": "piston cup socket and carrier bore",
   "fit": "press",
   "files": "la-tube-rod"
  },
  {
   "feature": "OD",
   "exact": "Ø18",
   "mates": "leaf hubs and the four collars (M3 grubs)",
   "fit": "slide",
   "files": "la-tube-rod"
  },
  {
   "feature": "bore",
   "exact": "Ø14",
   "mates": "bounce gas (no contact)",
   "fit": "designed",
   "files": "la-tube-rod"
  }
 ],
 "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 a cup and a separate carrier?",
   "a": "The seal wants a short, light, true land right at the working face; the magnets want to sit under the stator between the two leaves. A tube rod joins them through leaf 1's hub."
  },
  {
   "q": "Is it the same alternator as the free-piston generator's?",
   "a": "Yes: the same stator, coil, magnets and magnet spacing, so the same force constant; only the piston is new, with a leaf at each end of the magnets."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "la-piston-cup-48x24",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/la-piston-cup-48x24.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/la-piston-cup-48x24.stl",
   "note": "piston cup: land Ø48.00 × 24 (the clearance seal), crown 5 thick, skirt bore Ø42, hub boss Ø26 with the Ø18 tube-rod socket from 9 to the top, 3 × M3 tapped (Ø2.5 × 4) on r 17 for the mass discs"
  },
  {
   "file": "la-magnet-carrier-47x56",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/la-magnet-carrier-47x56.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/la-magnet-carrier-47x56.stl",
   "note": "magnet carrier Ø47 × 56, Ø18 bore (pressed on the tube rod), 4 rows × 10 radial pockets Ø12 × 3 at z 7, 21, 35, 49 (pocket floor plane 19.7 from the axis), cavity r 12–15 vented by 4 × Ø3 through each end web"
  },
  {
   "file": "la-tube-rod-18x14x108.15",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/la-tube-rod-18x14x108.15.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/la-tube-rod-18x14x108.15.stl",
   "note": "tube rod Ø18 / Ø14 × 108.15 (closed module): piston cup socket to the top of leaf 2's upper collar"
  },
  {
   "file": "la-tube-rod-18x14x151.70",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/la-tube-rod-18x14x151.70.step",
   "stl": "https://xemstudio.com/files/hardware/linear-alternator-module-mover-2in/la-tube-rod-18x14x151.70.stl",
   "note": "tube rod Ø18 / Ø14 × 151.70 (open-frame module): piston cup socket to the top of leaf 2's upper collar"
  }
 ],
 "markdown": "https://xemstudio.com/objects/linear-alternator-module-mover-2in/index.md"
}