# Round-belt generator drive: Ø84 crank pulley, 2208 generator pulley, Ø5 belts

> How do I belt a small generator off a Stirling engine's crank?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: Design values; 2208 rotor-top hole pattern from the gimbal-motor envelope on this site
- Page: https://xemstudio.com/objects/round-belt-generator-drive/ · JSON: https://xemstudio.com/api/geometry?object=round-belt-generator-drive · Plain text: https://xemstudio.com/objects/round-belt-generator-drive/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.** 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

- A Ø5 round belt from an Ø84 crank pulley (pitch Ø80) to an Ø16 pulley (pitch Ø13.33) bolted to a 2208 gimbal motor's rotor top: 6 : 1, so 600 rpm at the crank is 3600 rpm at the generator.
- Belt lengths on the centre line: 339.1 mm at 90 centres (horizontal gamma), 415.2 mm at 130 (walking-beam gamma). Round belts are cut to length and joined; tension by stretch.
- The belt and pulleys turn the crank's shaft power into motor speed; the electrical output on each engine's page comes from the motor's published KV and resistance.

## 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 |
|---|---|---|---|---|
| crank pulley bore | Ø8 | Ø8 crank shaft (M4 grub) | slide | crank-pulley* |
| grooves | Ø5 round, pitch Ø80 / Ø13.33 | Ø5 round belt | designed | all |
| pulley flange holes | 4 × Ø2.4 on 12 × 12 | M2 screws into the 2208 rotor top | designed | generator-pulley* |

## Sizes

| part | size |
|---|---|
| crank-pulley-84-b8 | Ø84 × 6, pitch Ø80, hub Ø20 |
| generator-pulley-2208-pd13.33 | Ø16 × 8, pitch Ø13.33 |
| round-belt-5-c90 | Ø5 × 339.1 |
| round-belt-5-c130 | Ø5 × 415.2 |

## Where the files are

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

## Free STEP/STL (4 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/round-belt-generator-drive/index.json

- crank-pulley-84-b8: [STEP](https://xemstudio.com/files/hardware/round-belt-generator-drive/crank-pulley-84-b8.step) · [STL](https://xemstudio.com/files/hardware/round-belt-generator-drive/crank-pulley-84-b8.stl) — crank pulley Ø84 × 6 with a Ø5 round-belt groove on pitch Ø80, hub Ø20 × 19.5, Ø8 bore, M4 tapped hub hole
- generator-pulley-2208-pd13.33: [STEP](https://xemstudio.com/files/hardware/round-belt-generator-drive/generator-pulley-2208-pd13.33.step) · [STL](https://xemstudio.com/files/hardware/round-belt-generator-drive/generator-pulley-2208-pd13.33.stl) — generator pulley for a 2208 rotor top: flange Ø24 × 3 with 4 × Ø2.4 (12 × 12), neck Ø8, pulley Ø16 × 8 with a Ø5 groove on pitch Ø13.33
- round-belt-5-c90: [STEP](https://xemstudio.com/files/hardware/round-belt-generator-drive/round-belt-5-c90.step) · [STL](https://xemstudio.com/files/hardware/round-belt-generator-drive/round-belt-5-c90.stl) — Ø5 round belt on pitch circles Ø80 and Ø13.33 at 90 centres: 339.1 mm long on its centre line
- round-belt-5-c130: [STEP](https://xemstudio.com/files/hardware/round-belt-generator-drive/round-belt-5-c130.step) · [STL](https://xemstudio.com/files/hardware/round-belt-generator-drive/round-belt-5-c130.stl) — Ø5 round belt on pitch circles Ø80 and Ø13.33 at 130 centres: 415.2 mm long on its centre line

## Questions

**What ratio?**

6 : 1: the 2208's KV 128 then gives about 28 V open circuit at 600 rpm at the crank.

## Fits with

- [2208 gimbal motor: outside envelope and mounting holes (Ø27.5 × 23, base M3 on 19 × 16, rotor M2 on 12 × 12)](https://xemstudio.com/objects/gimbal-motor-2208-envelope/)
- [Build list: Tri-clamp horizontal gamma generator, 2 in, chargeable](https://xemstudio.com/objects/list-tri-clamp-horizontal-gamma/)
- [Build list: Tri-clamp walking-beam gamma generator, 2 in, chargeable](https://xemstudio.com/objects/list-tri-clamp-walking-beam-gamma/)