# HTD generator drive: 210 T crank gear and a 2208 bracket (14 : 1)

> How do I gear a generator to a slow Stirling engine?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: Module 1, 20° involute (ISO 53) as the site's spur gears; the catalog's 15 T pinion, its 2208 adaptor and the 2208 envelope
- Page: https://xemstudio.com/objects/htd-generator-drive/ · JSON: https://xemstudio.com/api/geometry?object=htd-generator-drive · Plain text: https://xemstudio.com/objects/htd-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

- 210 : 15 = 14 : 1 at 112.5 centre distance: at 150 rpm the 2208 (KV 128, 14.4 Ω, published) turns 2100 rpm and makes 16.4 V open circuit.
- The bracket bolts to the seal cap's outer face with three M4; the motor's base takes four M3 countersunk screws from the bracket's back.

## 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 |
|---|---|---|---|---|
| gear bore | Ø12, M4 grub | Ø12 shaft | slide | gear-* |
| mesh | module 1, 210 : 15 at 112.5 centres | pinion-m1-15t-b6 | designed | gear-* |
| bracket holes | 3 × Ø4.5 on r 30; 4 × Ø3.4 countersunk 90° to Ø6 | shcs-m4x12; csk-m3x8 into the motor base | designed | motor-bracket-* |
| shaft hole | Ø30 | shaft and seal (no contact) | designed | motor-bracket-* |

## Sizes

| part | teeth | tip_mm | ratio |
|---|---|---|---|
| gear-m1-210t-b12 | 210 | 212.0 | 14.0 |
| motor-bracket-2208-3in |  |  |  |

## Where the files are

- ISO: [ISO 53 cylindrical gears, standard basic rack (20°, addendum 1 m, dedendum 1.25 m)](https://www.iso.org/standard/22952.html) — standard — dimensions are facts (verify at link)
- T-Motor (maker's store page): [GB2208 gimbal motor KV128: internal resistance 14.4 Ω](https://store.tmotor.com/goods-447-GB2208.html) — web — maker page; values are facts (verify at link)
- 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/htd-generator-drive/index.json

- gear-m1-210t-b12: [STEP](https://xemstudio.com/files/hardware/htd-generator-drive/gear-m1-210t-b12.step) · [STL](https://xemstudio.com/files/hardware/htd-generator-drive/gear-m1-210t-b12.stl) — crank gear module 1, 210 teeth, 20° (tip Ø212), 10 wide, hub Ø30 × 15, Ø12 bore, M4 radial tapped hole
- motor-bracket-2208-3in: [STEP](https://xemstudio.com/files/hardware/htd-generator-drive/motor-bracket-2208-3in.step) · [STL](https://xemstudio.com/files/hardware/htd-generator-drive/motor-bracket-2208-3in.stl) — generator bracket 5 thick: Ø76.2 disc on the seal cap (3 × M4 on r 30), arm to the motor 112.5 above the shaft, 2208 base holes countersunk

## Questions

**Why gear up 14 : 1?**

A slow engine turns a small generator too slowly to make useful voltage; 14 : 1 puts the 2208 near 2000 rpm.

## Fits with

- [Build list: HTD engine, 10 in tri-clamp (high-temperature-differential flat engine)](https://xemstudio.com/objects/list-htd-10in/)
- [Step-up gears for a generator inside a 2 in tri-clamp cross: 42 : 15, module 1](https://xemstudio.com/objects/tri-clamp-generator-step-up-gears/)
- [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/)