N8
Geneva Wheel

by David W. Henderson and Daina Taimina

The action of the Geneva Wheel is best understood by studying the QTVR. To see the geometric relationships, see the drawing (below).

The driving wheel is a circular disk (with a  sector removed) and a pin. As the driving wheel rotates, during

 

of each revolution the other wheel (in the shape of a Maltese Cross) is stationary. Then, during the next

 

of the revolution, the pin engages and the Maltese Cross is turned through angle .  By the Law of Sines:

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Often (but not in the case of Reuleax’s model N8) the Geneva Wheel is designed so that, in addition to the above,

 

in which case the angle at the pin in the figure will be a right angle. With this design the pin will slide more smoothly into the slot instead of hitting the edge of the slot with an audible click.