# Centrifugal (fly-ball) governor

> How does a fly-ball governor control speed?

- Category: Mechanisms › Linkages
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 161 (1868)
- Page: https://xemstudio.com/objects/flyball-governor-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=flyball-governor-mechanism · Plain text: https://xemstudio.com/objects/flyball-governor-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

- Two balls on arms hinged to the head of a spinning spindle fly outward as it turns faster; links from the arms lift a sleeve on the spindle, and the sleeve works the steam throttle (or any regulator), closing it as speed rises. Each ball settles where tan α = ω² r / g: at α = 30° and r = 54 mm the spindle turns 97.8 rpm.
- Arms 80 mm (Ø24 balls), pivots 14 mm from the axis, links 40 mm from the arms' midpoints to the sleeve; drawn at α = 30°, the sleeve pins 69.28 mm below the arm pivots.
- Brown's No. 161 (Watt's governor).
- Parts (each has its own page): governor-arm-80-ball-24, governor-head-16-ears-14, governor-sleeve-16-ears-14, four-bar-links, dowel-pins-metric, linear-shafts-h6.
- Brown's movement No. 161 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| arms | 2 × 80 mm, Ø24 balls |
| links | 2 pairs × 40 mm |
| angle drawn | 30° |
| speed at that angle | 97.8 rpm |

## 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. 161: figure, his text and an animation](https://507movements.com/mm_161.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/flyball-governor-mechanism/index.json · license: https://xemstudio.com/files/hardware/flyball-governor-mechanism/LICENSE.md

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

## Questions

**How does a fly-ball governor control speed?**

Two balls on arms hinged to the head of a spinning spindle fly outward as it turns faster; links from the arms lift a sleeve on the spindle, and the sleeve works the steam throttle (or any regulator), closing it as speed rises. Each ball settles where tan α = ω² r / g: at α = 30° and r = 54 mm the spindle turns 97.8 rpm.

## Fits with

- [Governor arm 80 mm with a Ø24 ball, Ø3 pivot and link holes](https://xemstudio.com/objects/governor-arm-80-ball-24/)
- [Governor head: Ø16 × 14 collar with forked ears, pivots 28 mm apart](https://xemstudio.com/objects/governor-head-16-ears-14/)
- [Governor sleeve: Ø16 × 20 sliding collar with ears 14 mm out](https://xemstudio.com/objects/governor-sleeve-16-ears-14/)
- [Four-bar links: flat links with 20 to 100 mm hole centres](https://xemstudio.com/objects/four-bar-links/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)