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Crank with closed channel yoke (uniform-speed reciprocation)

How can a crank give uniform straight-line speed? · Hardware · basis: Xem Studio design following Brown No. 354 (1868)

Also called: uniform velocity crank, constant speed yoke, crank channel yoke, manivela con yugo de velocidad uniforme, Kurbel mit Gleichlaufkulisse

Exact dimensions. True size, with no printing tolerance added.

sizes
4 in table

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.

Crank with closed channel yoke size chart

parametervalue
crank radius12 mm
stroke24 mm, uniform speed
channel3 mm, closed loop
speed48 mm per crank turn

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Henry T. Brown (1868, public domain)Five Hundred and Seven Mechanical Movements — scan on archive.orgwebPublisher's page; dimensions are facts
507movements.comBrown's movement No. 354: figure, his text and an animationwebPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

uniform-motion-crank-yoke-mechanism-assemblyAssembled mechanism, all parts placed at one pose (STEP keeps each part separate)STEP · STL
Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.
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Plain text: sheet.txt · JSON: /api/geometry?object=uniform-motion-crank-yoke-mechanism

Crank with closed channel yoke (uniform-speed reciprocation), isometric render of a generated part
Render of uniform-motion-crank-yoke-mechanism-assembly from the free STEP; not to scale.

Fits with

Crank disc Ø36 × 5, Ø5 bore, Ø3 pin hole at 12 mm, isometric render of a generated part
Crank disc Ø36 × 5, Ø5 bore, Ø3 pin hole at 12 mm36.0×36.0×5.0 mm★ 1 file
Uniform-motion yoke plate 60 × 40 × 8 with closed channel for a 12 mm crank, isometric render of a generated part
Uniform-motion yoke plate 60 × 40 × 8 with closed channel for a 12 mm crank60.0×40.0×8.0 mm★ 1 file
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long, isometric render of a generated part
Linear shafts Ø3 to Ø25 mm (h6), 100 to 1000 mm long10 sizes★ 70 files
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325), isometric render of a generated part
Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)5 sizes★ 23 files

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.