Input: rocker getting motion from a Watt steam engine.
Output: pink crank shaft.
Blue gear of tooth number Z1 is fixed to blue conrod.
Yellow gear of tooth number Z2 is fixed to yellow flywheel.
Z1 = Z2
The flywheel rotates two times faster than the crankshaft. It helps to reduce the flywheel size while keeping needed storage energy.
However the flywheel and the crankshaft are not of constant velocity.
This idea is taken from