Drag-link (double-crank) four-bar — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/drag-link-mechanism/  (CC BY 4.0)
Basis: Xem Studio drawing; classic mechanism (Brown No. 231)
Catalog version: 2026-10-20

Sizes: see table below
- A four-bar whose shortest link is the fixed frame: both cranks turn fully round. Grashof: s + l ≤ p + q (20 + 50 ≤ 45 + 40).
- Input turns at constant speed, output at varying speed — the base of quick-return drives and some shaper and press mechanisms.
- Built from four-bar links of the lengths in the table.
- Parts (each has its own page): four-bar-links, pins-3mm. Brown's movement No. 231 shows it (1868).

parameter  value
frame (shortest) s  20 mm
input crank  40 mm
coupler  50 mm
output crank  45 mm

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

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