Ross yoke kit (alpha Stirling with parallel cylinders) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/ross-yoke-kit/  (CC BY 4.0)
Basis: Andy Ross's yoke (1970s): a triangular rocker on a single crank gives two parallel pistons ~90° apart with near-straight-line motion; proportions a = 30, h = 20 for 16 mm strokes
Catalog version: 2026-10-20

Sizes: see table below
- Alpha engines need two pistons 90° out of phase; the usual V-twin crank puts the cylinders at 90°. The Ross yoke lets both cylinders sit side by side and parallel: a triangular rocker pivots on a short rocking link, its bottom corner rides the crank pin, and its two top corners drive the pistons through short con-rods. The geometry makes each piston's motion almost straight (low side load) and roughly 90° apart.
- Proportions: top pivots at ±a, crank pivot at −h below, rocking pivot near the centroid; a/h ≈ 1.5, crank throw ≈ h/2.5. With a 30 / h 20 / e 8 the strokes are ~16 mm and phase ~90°. Cylinder spacing = 2a = 60 mm... here the syringe block uses 34 mm spacing with the a = 30 yoke angled; use a = 17 for a dead-parallel block, or the 2× syringe block as the compact version.
- Parts: yoke, rocking link (frame to yoke centroid, 623 bearing), two con-rods, crank disc, cylinder block for two 10 mL syringes (the simplest alpha: one hot, one cold, a tube between), flywheel from the crank kit.
- LES: the alpha demonstrator with two syringes; the hot syringe sits in a tri-clamp hot end via the power head.

part  size  note
yoke  a 30, h 20 (or 40/25)  623 at centroid
rocking link  30  frame pivot
con-rods  45 × 2  Ø3 pins
crank  e 8 (stroke 16)  Ø5 shaft
cylinder block  2 × 10 mL syringes @ 34  alpha

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine
- Andy Ross: Making Stirling Engines (Ross yoke) — book — reference [verify license at link] — https://www.stirlingengine.com/
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 6 parts): https://xemstudio.com/files/hardware/ross-yoke-kit/index.json
API: https://xemstudio.com/api/geometry?object=ross-yoke-kit