Tusi couple: straight line from a gear rolling inside a ring twice its size — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/tusi-couple-straight-line-mechanism/  (CC BY 4.0)
Basis: Xem Studio design following Brown No. 329 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A planet of half the ring's pitch diameter rolls inside it (30 T in 60 T, carrier 15 mm): any point on the planet's pitch circle moves on a straight line through the ring's centre, 4 × 15 = 60 mm long — exact, not approximate.
- At the drawn carrier angle 40° the planet has turned −40° and the tracer pin sits at x = 22.98, y = 0; x = 60/2 · cos θ.
- Brown's No. 329 uses it to guide a piston rod without slides (cog-wheel inside a fixed internal gear of twice its diameter).
- Parts (each has its own page): internal-ring-gear-m1-60t, spur-gears-module-1, tusi-carrier-15, tusi-tracer-arm-15, dowel-pins-metric.
- Brown's movement No. 329 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
ring  60 T internal
planet  30 T
carrier  15 mm
stroke  60 mm, straight

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala
- 507movements.com: Brown's movement No. 329: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_329.html

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/tusi-couple-straight-line-mechanism/index.json
API: https://xemstudio.com/api/geometry?object=tusi-couple-straight-line-mechanism