# Step-up gears for a generator inside a 2 in tri-clamp cross: 42 : 15, module 1

> How do I speed up a small generator from a Stirling crankshaft inside a 2 inch tri-clamp cross?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: ISO 53 basic rack (20°, addendum 1 m, dedendum 1.25 m), involute flanks as the spur gears on this site; centre distance m (z1 + z2) / 2; tooth counts set by the room in the cross; rotor-top holes from the 2208 listing
- Page: https://xemstudio.com/objects/tri-clamp-generator-step-up-gears/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-generator-step-up-gears · Plain text: https://xemstudio.com/objects/tri-clamp-generator-step-up-gears/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

- The crank gear (42 teeth, tip Ø44) sits on the −X crankshaft beside the crank, in place of one flywheel disc and just as heavy; the 15-tooth pinion turns with the motor's rotor. Centre distance 28.5 mm, ratio 2.8 : 1.
- The pinion rides on an adaptor: a Ø18 × 2 flange bolted to the rotor top with four M2 × 4 (their heads on the flange's outer face) and a Ø6 stub through the pinion, which an M3 grub holds. The rotor's holes sit at r 6, inside the pinion's teeth, so the pinion cannot be bolted on directly.
- Why 2.8 and not more: the motor's Ø27.5 can lies over the crank, so its axis has to be at least 13 + 13.75 mm above the crankshaft (the crank's con-rod eyes sweep R 13), and the crank gear has to turn inside the Ø47.5 bore. 42 : 15 at module 1 puts the can 1.75 mm clear of the crank and the gear tip 1.75 mm inside the bore.
- Both gears are drawn at exact size with no backlash; their teeth are a mating feature (see Mating features).

## 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 |
|---|---|---|---|---|
| teeth | module 1, 20°, 42 T and 15 T at 28.5 centre distance, no backlash | each other | designed | all |
| crank-gear bore | Ø3 | Ø3 crankshaft (M3 grub, radial from the rim) | slide | crank-gear-* |
| pinion bore | Ø6 | adaptor stub Ø6 (M3 grub) | slide | pinion-m1-* |
| adaptor stub | Ø6 | pinion bore | slide | pinion-adaptor-* |
| adaptor flange holes | 4 × Ø2.4 on the 12 / 12 pattern | shcs-m2x4 into the motor rotor top | designed | pinion-adaptor-* |
| grub holes | Ø2.5 (M3 tapped) | set-m3x10 (gear), set-m3x3 (pinion) | designed | crank-gear-* |
| grub hole | Ø2.5 (M3 tapped) | set-m3x3 onto the adaptor stub (ends at r 6, inside the r 6.25 root) | designed | pinion-m1-* |

## Sizes

| part | teeth | pitch_dia_mm | tip_dia_mm | width_mm | bore_mm |
|---|---|---|---|---|---|
| crank gear | 42 | 42.0 | 44.0 | 12.0 | 3.0 |
| pinion | 15 | 15.0 | 17.0 | 10.0 | 6.0 |
| adaptor |  |  | 18.0 | 14.0 |  |

## Where the files are

- ISO: [ISO 53 cylindrical gears, standard basic rack (20°, addendum 1 m, dedendum 1.25 m), as the involute spur gears on this site](https://www.iso.org/standard/22952.html) — standard — dimensions are facts (verify at link)
- GetFPV (product listing): [Tiger GB2208-80 gimbal motor: 27.5 × 23, 4.5 hollow shaft, stator 4-M3 on 19 × 16, rotor 4-M2 on 12 × 12](https://www.getfpv.com/tiger-gb2208-80-brushless-gimbal-motor-hollow-shaft.html) — web — vendor page; dimensions are facts (verify at link)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (3 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-generator-step-up-gears/index.json

- crank-gear-m1-42t-b3: [STEP](https://xemstudio.com/files/hardware/tri-clamp-generator-step-up-gears/crank-gear-m1-42t-b3.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-generator-step-up-gears/crank-gear-m1-42t-b3.stl) — crank gear: module 1, 42 teeth, 20° (pitch Ø42, tip Ø44), 12 wide, Ø3 bore, radial M3 tapped hole (Ø2.5) at mid-width
- pinion-m1-15t-b6: [STEP](https://xemstudio.com/files/hardware/tri-clamp-generator-step-up-gears/pinion-m1-15t-b6.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-generator-step-up-gears/pinion-m1-15t-b6.stl) — pinion: module 1, 15 teeth, 20° (pitch Ø15, tip Ø17), 10 wide, Ø6 bore, radial M3 tapped hole (Ø2.5)
- pinion-adaptor-2208: [STEP](https://xemstudio.com/files/hardware/tri-clamp-generator-step-up-gears/pinion-adaptor-2208.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-generator-step-up-gears/pinion-adaptor-2208.stl) — pinion adaptor: flange Ø18 × 2 with 4 × Ø2.4 on the 12 / 12 rotor pattern, Ø6 stub 12 long

## Questions

**What ratio, and why not more?**

2.8 : 1. The motor can has to clear the crank and the gear has to fit the 2 in bore; that sets the centre distance at 28.5 mm.

**How much do the gears lose?**

A single spur mesh like this loses roughly 1 to 3 % of the power through it; the estimate on the build list uses that range.

## 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/)
- [Spur gears, involute 20°: module 0.5, 1 and 2, 12–60 teeth](https://xemstudio.com/objects/spur-gears-involute/)
- [Crankcase flywheels: Ø44 × 12 disc and Ø42 pocket flywheel on a Ø3 shaft, inside a 2 in tri-clamp fitting](https://xemstudio.com/objects/tri-clamp-crankcase-flywheel/)
- [Motor-mount plate for a 2 in tri-clamp cross: clamps between two faces, holds a 2208 gimbal motor inside](https://xemstudio.com/objects/tri-clamp-motor-mount-plate/)
- [Build list: Tri-clamp sealed diaphragm generator, 2 in](https://xemstudio.com/objects/list-tri-clamp-sealed-diaphragm-generator/)