The machine's gearing is very straightforward. The motor drives a pulley, which drives an 8-tooth gear on the other end of a shaft. The 8-tooth gear drives the 40-tooth main gear that has the connecting rod mounted to it. Every 5 turns of the pulley is one turn of the crank, one back and forth cycle of the slider, and one domino released.
The 40-tooth crank gear also drives a 24-tooth gear on the same shaft, which drives a 24-tooth crown gear. That 24-tooth crown gear drives an 8-tooth pinion which meshes with a 40-tooth gear on the main axle with the drive wheels on it.
That makes for a 5:1 reduction from the crank to the main axle so that the machine releases five dominoes for every turn of the drive wheels.