# One pinion driving an internal and a spur gear on one axis (two speeds)

> How can one pinion drive two gears at different speeds on the same axis?

- Category: Mechanisms › Gears
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 55 (1868)
- Page: https://xemstudio.com/objects/pinion-driving-internal-and-spur-gear-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=pinion-driving-internal-and-spur-gear-mechanism · Plain text: https://xemstudio.com/objects/pinion-driving-internal-and-spur-gear-mechanism/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- 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

- A pinion sits between a ring gear and a spur gear that share an axis: it drives the ring the same way at 20/60 of its speed and the spur gear the opposite way at 20/20 — two speeds and two directions from one pinion.
- The tooth counts must satisfy N_ring = N_spur + 2·N_pinion (60 = 20 + 2 × 20) so both meshes sit at the same 20 mm centre distance.
- It is the fixed-carrier (star) form of an epicyclic train; Brown's No. 55 draws it with the two driven gears on one shaft.
- Parts (each has its own page): internal-ring-gear-m1-60t, spur-gears-module-1.
- Brown's movement No. 55 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| ring | 60 T internal |
| spur gear | 20 T |
| pinion | 20 T |
| centre distance | 20 mm |
| speeds (pinion = 1) | ring 1/3 same way; spur 1 opposite |

## Where the files are

- Henry T. Brown (1868, public domain): [Five Hundred and Seven Mechanical Movements — scan on archive.org](https://archive.org/details/fivehundredseven00browiala) — web — Publisher's page; dimensions are facts
- 507movements.com: [Brown's movement No. 55: figure, his text and an animation](https://507movements.com/mm_055.html) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/pinion-driving-internal-and-spur-gear-mechanism/index.json · license: https://xemstudio.com/files/hardware/pinion-driving-internal-and-spur-gear-mechanism/LICENSE.md

- pinion-driving-internal-and-spur-gear-mechanism-assembly: [STEP](https://xemstudio.com/files/hardware/pinion-driving-internal-and-spur-gear-mechanism/pinion-driving-internal-and-spur-gear-mechanism-assembly.step) · [STL](https://xemstudio.com/files/hardware/pinion-driving-internal-and-spur-gear-mechanism/pinion-driving-internal-and-spur-gear-mechanism-assembly.stl) — Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)

## Questions

**How can one pinion drive two gears at different speeds on the same axis?**

A pinion sits between a ring gear and a spur gear that share an axis: it drives the ring the same way at 20/60 of its speed and the spur gear the opposite way at 20/20 — two speeds and two directions from one pinion.

## Fits with

- [Internal (ring) gear, module 1, 60 teeth, Ø80](https://xemstudio.com/objects/internal-ring-gear-m1-60t/)
- [Spur gears, module 1: 10 to 80 teeth (20° involute)](https://xemstudio.com/objects/spur-gears-module-1/)