# Build list: Linear alternator module, 2 in, open frame (exposed flexures)

> What parts do I need to build a Linear alternator module, 2 in, open frame (exposed flexures)?

- Category: Electronics › Generators & alternators
- Kind: List / guide
- Basis: Every part is a free STEP/STL on this site or a standard part with its own page; quantities are the full count, every screw, nut, pin, gasket and clamp.
- Page: https://xemstudio.com/objects/list-linear-alternator-module-2in-open/ · JSON: https://xemstudio.com/api/geometry?object=list-linear-alternator-module-2in-open · Plain text: https://xemstudio.com/objects/list-linear-alternator-module-2in-open/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- The same linear alternator on an open frame: it clamps on the end of an unpressurised engine with one 2 in ferrule face, and the leaves, the mover's ends and the stator sit in the open where you can see and reach them.
- Ø48 piston ±5 mm (±6 max) · moving mass 899 g · leaves 8851 N/m · Bl 28.8 N/A · coil 3.40 Ω, ≈25 mH · f₀ 15.8 Hz on the leaves alone · back open to the room · 167.7 mm from face A
- The version I use most. Face A is the same: the 42 mm bored spool with the Ø48 clearance-seal piston cup, clamped on the end of a desk engine, the power end of a tri-clamp Stirling or any 2 in device at 1 bar. Behind the piston there is no bounce space: its back breathes to the room.
- The spool's second ferrule carries the open frame, clamped like an end cap: frame base with leaf 1 on its seat, a clamp ring on 10 mm posts, the stator sleeve with the same stator and coil as the closed module, a top plate on 5 mm posts, the seat ring with leaf 2 and its clamp ring. The same mover, leaves, magnets and coil as the closed module: only the tube rod is longer.
- Nothing covers the leaves: you can watch them work, change leaf set or mass discs with a screwdriver, and centre the mover by eye. The datasheet compares both versions and says when to use which.
- Leaf set A (0.8) is the standard build; set B (0.5, on rim shims) and the mass discs are tuning parts. The same leaves also clamp between half gaskets in any spool-to-spool joint, as in the closed module.

## Sizes

| subsystem | object | parts | qty | note |
|---|---|---|---|---|
|  | linear-alternator-module-spools-2in | spool-2in-42mm-bored-48.00 | 1 | face A (to the engine) and the piston's cylinder; its second ferrule carries the frame base |
|  | linear-alternator-module-open-frame-2in | la-frame-base-2in-ferrule | 1 | clamped on the spool's second ferrule; leaf 1's seat on top |
|  | tri-clamp-gasket | tc-gasket-2in | 2 | Type B at face A (to the engine) and between the spool and the frame base |
|  | tri-clamp-clamps | clamp-half-2in | 4 | two standard 2 in clamps: face A to the engine, the spool to the frame base |
|  | socket-head-cap-screws-metric | shcs-m5x30 | 4 | two per clamp |
|  | hex-nuts-metric | nut-m5 | 4 | in the clamps' hex traps |
|  | tri-clamp-flexure-leaf | leaf-2in-piston-t0.8 | 2 | choose one leaf set, A (standard 0.8): leaf 1 in the frame base's seat, leaf 2 (turned over, opposite hand) in the seat ring |
|  | linear-alternator-module-tuning-2in | leaf-2in-piston-t0.5 | 2 | choose one leaf set, B (soft 0.5, tuning): in place of the 0.8 leaves; leaf 2 turned over |
|  | linear-alternator-module-tuning-2in | la-rim-shim-64x0.3 | 2 | choose one leaf set, B (soft 0.5, tuning): one under each soft leaf's rim in its seat |
|  | linear-alternator-module-open-frame-2in | la-frame-leaf-clamp-ring-80-posts10 | 1 | on leaf 1's rim, posts up |
|  | linear-alternator-module-open-frame-2in | la-frame-stator-sleeve-48x66 | 1 | on the posts; the stator round it |
|  | linear-alternator-module-open-frame-2in | la-frame-stator-top-plate-80-posts5 | 1 | on the sleeve's top flange, posts up |
|  | linear-alternator-module-open-frame-2in | la-frame-leaf-seat-ring-80 | 1 | on the top plate's posts; leaf 2's seat on top |
|  | linear-alternator-module-open-frame-2in | la-frame-leaf-clamp-ring-80 | 1 | on leaf 2's rim |
|  | socket-head-cap-screws-metric | shcs-m3x25 | 3 | down through the sleeve's lower flange, the posts and the lower clamp ring into the frame base |
|  | socket-head-cap-screws-metric | shcs-m3x12 | 3 | down through the top plate into the sleeve's top flange |
|  | socket-head-cap-screws-metric | shcs-m3x16 | 3 | down through the upper clamp ring and the seat ring into the top plate's posts |
|  | linear-alternator-module-mover-2in | la-piston-cup-48x24 | 1 | in the 42 bored spool, crown toward face A |
|  | linear-alternator-module-mover-2in | la-tube-rod-18x14x151.70 | 1 | pressed into the cup's socket; through both leaves |
|  | linear-alternator-module-mover-2in | la-magnet-carrier-47x56 | 1 | pressed on the tube rod, centred in the stator sleeve |
|  | neodymium-disc-magnets | magnet-12x3 | 40 | 4 rows of 10 in the carrier, faces out: S, N, N, S from face A |
|  | fpse-hub-collars | fpse-collar-18x28 | 4 | either side of each leaf's hub on the tube rod |
|  | set-screws-metric | set-m3x4 | 4 | one grub per collar |
|  | fpse-linear-alternator-stator | fpse-stator-pack-43deg | 8 | round the stator sleeve at the magnets' centre |
|  | fpse-linear-alternator-stator | fpse-bobbin-65 | 1 | between the teeth; slid over the sleeve's Ø64 top flange first |
|  | fpse-linear-alternator-stator | fpse-coil-300t | 1 | 300 turns of 0.71 mm enamelled wire on the bobbin; the leads leave through the housing |
|  | fpse-linear-alternator-stator | fpse-stator-housing-half | 2 | clamp the packs onto the sleeve |
|  | socket-head-cap-screws-metric | shcs-m4x20 | 4 | stator housing ears |
|  | hex-nuts-metric | nut-m4 | 4 | stator housing ears |
|  | linear-alternator-module-tuning-2in | la-mass-disc-41x26x4 | 4 | optional (tuning): add-on mass discs on the crown inside the cup, 0 to 4 |
|  | socket-head-cap-screws-metric | shcs-m3x20 | 3 | optional (tuning): hold 4 discs (3 × M3 × 16 for 3, × 12 for 2, × 8 for 1) |
|  | linear-alternator-module-2in-datasheet |  | 1 | load resistor: non-inductive, power rated above the expected output; value on the datasheet: bought, not drawn |
|  | linear-alternator-module-2in-datasheet |  | 1 | series capacitor: non-polar, C = 1/(ω² L) for the running frequency (datasheet), rated above the voltage across it: bought, not drawn |

## Where the files are

- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Build order

1. Magnets into the carrier (rows S, N, N, S from the end that faces A), carrier pressed on the tube rod at its drawn place, tube pressed into the cup's socket. Mass discs on the crown now if the tuning needs them.
2. Coil on its bobbin over the sleeve's Ø64 top flange to the middle; eight stator packs round the sleeve at the coil; housing halves with 4 × M4 × 20. Leads out through the housing's hole.
3. 42 bored spool face A down. Mover in, crown down, until the crown is 9.00 below face A (depth gauge). Type B gasket and frame base on the spool's top ferrule; clamp. Collar on the tube, leaf 1 into the base's seat, collar; lower clamp ring posts up; the sleeve with its stator onto the posts; 3 × M3 × 25 into the base; grubs.
4. Top plate on the sleeve (3 × M3 × 12), seat ring on its posts, collar, leaf 2 turned over into the seat, upper clamp ring (3 × M3 × 16), collar; check the crown is still at 9.00 and the mover moves freely ±6 by hand from face A.
5. Face A: Type B gasket and clamp onto the engine. Load resistor and capacitor on the leads before the engine runs.

All printed STLs: https://xemstudio.com/objects/list-linear-alternator-module-2in-open/stl-list.txt

## Questions

**When do I use the open frame?**

On engines at 1 bar: desk and demo engines, the cold or power end of a tri-clamp Stirling, quick swaps, and whenever you want to see and retune the leaves. For a charged engine, a loop or a ring, use the closed module.

**Why is its frequency lower?**

Nothing pushes back on the piston but the leaves and the engine's own gas: 15.8 Hz on the leaves alone, higher on an engine (the datasheet lists it for engine volumes from 50 to 400 cm³). The closed module's bounce space is the stiff spring that the open frame leaves out.

**Where is the electricity?**

Two leads from the coil on the stator housing. Always connect the load before the engine runs.

## Fits with

- [Linear alternator module, 2 in tri-clamp: datasheet, closed and open frame (mass, stiffness, frequency, Bl, R, L, stroke, pressure) and test procedure](https://xemstudio.com/objects/linear-alternator-module-2in-datasheet/)
- [Build list: Linear alternator module, 2 in, closed (sealed bounce space, chargeable)](https://xemstudio.com/objects/list-linear-alternator-module-2in-closed/)
- [Linear alternator module open frame, 2 in: frame base, leaf seats, clamp rings, stator sleeve and top plate](https://xemstudio.com/objects/linear-alternator-module-open-frame-2in/)
- [Linear alternator module mover: Ø48 piston cup, 40-magnet carrier and tube rod, sprung on two leaves](https://xemstudio.com/objects/linear-alternator-module-mover-2in/)
- [Linear alternator module spools: 2 in × 42 mm bored Ø48.00 and 2 in × 25.4 mm (fabrication spec)](https://xemstudio.com/objects/linear-alternator-module-spools-2in/)
- [Linear alternator module tuning parts: add-on mass discs, the soft 0.5 mm leaf and its rim shim](https://xemstudio.com/objects/linear-alternator-module-tuning-2in/)
- [Moving-magnet linear alternator stator outside a 2 in tri-clamp spool: laminated two-tooth stator, one coil](https://xemstudio.com/objects/fpse-linear-alternator-stator/)
- [Tri-clamp flexure leaf: spiral planar spring clamped in a 2 in joint like a gasket (displacer and piston)](https://xemstudio.com/objects/tri-clamp-flexure-leaf/)
- [Build list: Free-piston Stirling, 2 in tri-clamp (flexure-suspended)](https://xemstudio.com/objects/list-free-piston-2in/)