Cast aluminum and wood (painted) on a vertical panel.
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The cogwheel or pinion rotating on the horizontal shaft is driving the large crown wheel. The pinion runs at constant speed because it is on the driving shaft but that of the crown wheel varies at every point from slower to faster movement because it rotates on a point off-center.
[Virginia Downward & William M. Clark, 1930]
The crown wheel gear was popular with renaissance engineers.It was used in early clock escapements as in the verge and foliot shown in Reuleaux-Voigt model X-1. The teeth act normal to the face of the gear wheel as in this model. Examples of a crown wheel gear and pinion can be found in the manuscripts of Leonardo da Vinci such as in the Codex Madrid Folio 17 recto. See KMODDL references for on-line access. FCM.