Found this post on Stumblr about simple animations that explain somewhat complex machines. My favorite is the Malta Cross, or Geneva Mechanism.
This is a drive mechanism where the drive gear rotates continuously and the output gear moves intermittently. The peg rides down the slot turning the output gear while the semi-disc of the drive fear then rides into an cutout of the output gear preventing rotation until the peg comes around again. This is used in film projectors, where the film stops in front of the projector bulb for a fraction of a second (usually 1/24th) before moving on.
A motion-picture camera must be able to advance the medium rapidly enough to permit at least 16 separate exposures per second, while at the same time bringing each frame to a full stop to record a sharp image. The principal technology that creates this intermittent movement is the Geneva wheel mechanism, in which a four-slotted star wheel, or “Maltese cross,” converts the tension of the mainspring to the ticking of toothed gears [Historical notes for N08-Geneva Wheel]
It is also used to interrupt the drive force in a mechanical clock or watch to keep the spring tension within range. These geneva devices have a limited number of slots so that when it gets to the end it just stops.
Geneva wheels having the form of the driven wheel were also used in mechanical watches, but not in a drive, rather to limit the tension of the spring, such that it would operate only in the range where its elastic force is nearly linear. If one of the slots of the driven wheel is occluded, the number of rotations the drive wheel can make is limited. In watches, the “drive” wheel is the one that winds up the spring, and the Geneva wheel with four or five spokes and one closed slot prevents overwinding (and also complete unwinding) of the spring. This so-called Geneva stop or “Geneva stop work” was the invention of 17th or 18th century watchmakers. [Wikipedia]
Here’s a video of the Geneva Mechanism at work:
Check out the rest of the cool mechanical gifs at the source link below.
-M
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