# Crank with closed channel yoke (uniform-speed reciprocation)

> How can a crank give uniform straight-line speed?

- Category: Mechanisms › Cams
- Kind: Hardware
- Basis: Xem Studio design following Brown No. 354 (1868)
- Page: https://xemstudio.com/objects/uniform-motion-crank-yoke-mechanism/ · JSON: https://xemstudio.com/api/geometry?object=uniform-motion-crank-yoke-mechanism · Plain text: https://xemstudio.com/objects/uniform-motion-crank-yoke-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 plain crank pin runs in a closed channel cut in the crosshead instead of a straight slot. The channel's shape is the pin's path relative to a crosshead moving at constant speed, so the crosshead travels 24 mm out at uniform speed during half a turn and back during the other half — a crank made to behave like a heart cam.
- Drawn at θ = 50°: crosshead at x = -5.33 mm, the Ø3 pin touching both walls of the 3 mm channel. Direction reverses sharply at the channel's two points (θ = 0° and 180°), the price of uniform speed.
- Brown's No. 354 (crank and slotted cross-head modified for uniform velocity, from No. 93).
- Parts (each has its own page): crank-disc-36-pin-r12, uniform-motion-yoke-plate-60x40-r12, linear-shafts-h6, dowel-pins-metric.
- Brown's movement No. 354 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

## Sizes

| parameter | value |
|---|---|
| crank radius | 12 mm |
| stroke | 24 mm, uniform speed |
| channel | 3 mm, closed loop |
| speed | 48 mm per crank turn |

## 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. 354: figure, his text and an animation](https://507movements.com/mm_354.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/uniform-motion-crank-yoke-mechanism/index.json · license: https://xemstudio.com/files/hardware/uniform-motion-crank-yoke-mechanism/LICENSE.md

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

## Questions

**How can a crank give uniform straight-line speed?**

A plain crank pin runs in a closed channel cut in the crosshead instead of a straight slot. The channel's shape is the pin's path relative to a crosshead moving at constant speed, so the crosshead travels 24 mm out at uniform speed during half a turn and back during the other half — a crank made to behave like a heart cam.

## Fits with

- [Crank disc Ø36 × 5, Ø5 bore, Ø3 pin hole at 12 mm](https://xemstudio.com/objects/crank-disc-36-pin-r12/)
- [Uniform-motion yoke plate 60 × 40 × 8 with closed channel for a 12 mm crank](https://xemstudio.com/objects/uniform-motion-yoke-plate-60x40-r12/)
- [Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long](https://xemstudio.com/objects/linear-shafts-h6/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)