Movement No. 35 presents a highly inventive mechanism for converting uniform rotary input into variable rotary output — using an elliptical gear, a spring-loaded pinion, and a slotted bar in a clever compound arrangement. At the heart of the system is an elliptical gear, whose radius continuously changes as it rotates — being longer along the major axis and shorter along the minor axis. A slotted bar is pivotally mounted so that it turns loosely on the shaft of this elliptical gear, meaning it is centered on the same axis but is free to rotate independently. A small spur pinion is mounted at the end of this bar and meshes with the teeth of the elliptical gear. As the elliptical gear rotates, its varying radius causes the contact point between the pinion and the elliptical gear to move closer and farther from the central shaft. The slot cut into the bar accommodates precisely this variation — the pinion’s bearing slides along the slot to follow the continuously changing radius of the elliptical gear surface, ensuring that the pinion always remains properly engaged with the gear teeth regardless of the current radius. A spring applied to the pinion’s bearing keeps it pressed firmly against the elliptical gear at all times, maintaining positive tooth engagement through the full rotation cycle. Because the pinion is walking along the profile of the elliptical gear, the bar carrying the pinion is driven at a continuously varying angular velocity — fast when the pinion contacts the shorter minor-axis region of the ellipse, and slow when it traverses the longer major-axis region. This produces a smoothly varying, cyclically repeating output rotation from a perfectly uniform input — a motion profile highly useful in machinery requiring periodic speed variation.
35. Variable rotary motion produced by uniform rotary motion. The small spur-pinion works in a slot cut in the bar, which turns loosely upon the shaft of the elliptical gear. The bearing of the pinion-shaft has applied to it a spring, which keeps it engaged; the slot in the bar is to allow for the variation of length of radius of the elliptical gear.