# Linear alternator housing for Ø80 and Ø100 flexures (2 in / 3 in)

> What housing holds the linear alternator stator on a free-piston engine?

- Category: Stirling engines › Free-piston
- Kind: Hardware
- Basis: Rim screw circle of the flexure head (R35.2 for Ø80, R44 for Ø100 flexures); sleeve pocket at Ø60.5; M3 clearance Ø3.4
- Page: https://xemstudio.com/objects/linear-alternator-housing/ · JSON: https://xemstudio.com/api/geometry?object=linear-alternator-housing · Plain text: https://xemstudio.com/objects/linear-alternator-housing/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- The stator body: a Ø63.7 barrel 36 tall between a base flange and a top flange (Ø96 for the 2 in, Ø116 for the 3 in), each 4 thick.
- From the top, a Ø60.5 pocket (fit: socket) takes the back-iron sleeve on a 2 mm ledge; a Ø40 passage lets the Ø35 mover through without contact; a 2.5 × 3 slot lets the leads out.
- 3 × Ø3.4 holes on the flexure head's rim circle (R35.2 or R44) bolt it to standoffs above flexure stack A; the coil centre sits 21 mm above its underside.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| sleeve pocket | Ø60.5 | back-iron sleeve OD | socket | alt-housing-* |
| housing rim holes | Ø3.4 | M3 screw clearance | designed | alt-housing-* |
| mover passage | Ø40 | Ø35 mover (no contact) | designed | alt-housing-* |

## Sizes

| file | flexure | flanges | rim circle | height | sleeve pocket | mover passage |
|---|---|---|---|---|---|---|
| alt-housing-2in-flex80 | Ø80 (2 in) | Ø96 × 4 | R35.2 | 36 | 60.5 | 40 |
| alt-housing-3in-flex100 | Ø100 (3 in) | Ø116 × 4 | R44 | 36 | 60.5 | 40 |

## Where the files are

- NASA (NTRS, public domain): [Linear alternator design for free-piston Stirling convertors (2005)](https://ntrs.nasa.gov/search?q=20050182934) — PDF — US Government work, public domain
- NASA (NTRS, public domain): [Sunpower/NASA 80 We free-piston Stirling convertor (2002)](https://ntrs.nasa.gov/search?q=20020047256) — PDF — US Government work, public domain
- Wikipedia: [Linear alternator](https://en.wikipedia.org/wiki/Linear_alternator) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Free-piston engine](https://en.wikipedia.org/wiki/Free-piston_engine) — web — CC BY-SA 4.0 (text)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (2 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/linear-alternator-housing/index.json

- alt-housing-2in-flex80: [STEP](https://xemstudio.com/files/hardware/linear-alternator-kit/alt-housing-2in-flex80.step) · [STL](https://xemstudio.com/files/hardware/linear-alternator-kit/alt-housing-2in-flex80.stl) — 2in housing: Ø96 base and top flanges with 3 × M3 on the R35.2 rim circle (same as the flexure head), pocket for the back-iron sleeve on a 2 mm ledge, Ø40 mover passage, lead slot; 36 tall
- alt-housing-3in-flex100: [STEP](https://xemstudio.com/files/hardware/linear-alternator-kit/alt-housing-3in-flex100.step) · [STL](https://xemstudio.com/files/hardware/linear-alternator-kit/alt-housing-3in-flex100.stl) — 3in housing: Ø116 base and top flanges with 3 × M3 on the R44 rim circle (same as the flexure head), pocket for the back-iron sleeve on a 2 mm ledge, Ø40 mover passage, lead slot; 36 tall

## How it fits

### Goes in or on
- [Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats](https://xemstudio.com/objects/tri-clamp-flexure-head/): on standoffs on the flexure head's rim screws

### Connects to
- [Linear alternator back-iron sleeve Ø60.5 × Ø52.5 × 30](https://xemstudio.com/objects/linear-alternator-back-iron-sleeve/): sleeve in the Ø60.5 pocket
- [Linear alternator cap ring, Ø96 and Ø116](https://xemstudio.com/objects/linear-alternator-cap-ring/): cap on the top flange

### Also needed
- [Threaded standoffs, M2.5 and M3 (hex and round)](https://xemstudio.com/objects/threaded-standoffs-metric/): M3 × 30 standoffs
- [Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)](https://xemstudio.com/objects/socket-head-cap-screws-metric/): M3 × 10 / 12 / 16

## Questions

**How does the linear alternator mount on the free-piston engine?**

Its base flange sits on 3 × M3 × 30 standoffs above flexure stack A, on the flexure head's rim circle (R35.2 for 2 in).

**Does it fit a 1.5 in engine?**

No: the Ø60 flexures of the 1.5 in engine are too small for this stator.

## Fits with

- [Linear alternator cap ring, Ø96 and Ø116](https://xemstudio.com/objects/linear-alternator-cap-ring/)
- [Linear alternator back-iron sleeve Ø60.5 × Ø52.5 × 30](https://xemstudio.com/objects/linear-alternator-back-iron-sleeve/)
- [Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats](https://xemstudio.com/objects/tri-clamp-flexure-head/)
- [Threaded standoffs, M2.5 and M3 (hex and round)](https://xemstudio.com/objects/threaded-standoffs-metric/)
- [Build list: Free-piston Stirling, 2 in tri-clamp (flexure-suspended)](https://xemstudio.com/objects/list-free-piston-2in/)