Ordinary crank motion

Only the input is driven; every other part of this model moves by physics (MuJoCo), and its ratios are measured. Run it live, change its parameters, or switch the friction off to see the output stop.

Modelled as

The crank-wheel (8 cm, spoked) turns clockwise at 30 rpm and is the only driven joint; its crank-pin is 4 cm from the centre. The connecting-rod (13 cm) turns on the pin and is pinned to the cross-head, which slides between fixed guides. The cross-head moves 8 cm to and fro, twice the throw, not harmonically: x = r cos t + sqrt(L^2 - r^2 sin^2 t), the rod obliquity hurrying it through the half-stroke nearer the crank.

Measured

Slopes of the cross-head against the crank: -0.0400 (ideal -0.03995) at 90 deg, -0.0346 (-0.03452) at 45 deg, -0.0220 (-0.02198) at 135 deg, r2 0.9994-1.0000; stroke -8.000..0.000 cm (ideal 8). Max penetration 0.00 mm (pins only).

Notes

A pure pin-joint mechanism: the cross-head guides are the slide joint (drawn); the faster-than-harmonic half of the stroke is the rod obliquity.

Film (MP4) · GIF · Still (PNG) · Spec (YAML) · Model (MJCF)