# Gears - Design and implementation.

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Gears are in tons of games, and they've always been sort of a mystery to me. From designing them (2D or 3D) so that the teeth line up no matter the size of the gear itself, how fast to rotate them so that they always appear interlocked.. etc. Gears are so simple on the surface, but pretty complex once you really get down to it. I would imagine the rotation speed of gears would have something to do with the ratio of teeth between the connecting gears.. but this is just a hunch. Then there's the whole problem of designing them. You can create a large gear that has 50 evenly spaced teeth, and a smaller gear that has 20 teeth.. but somehow they have to be designed so that the space between each tooth on the smaller gear matches the width of the teeth on the larger gear and vice versa. I really don't know how else to explain it. Has anyone ever stumbled across any info about this topic? Example http://img297.imageshack.us/img297/1925/42271873ma3.png

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There's some math going on, of course, but it's relatively simple math. Two gears that work on each other will need equally sized teeth (or at least, teeth that grip into each other tightly), but the number of teeth depends on their diameter. Their speed ratio is the inverse of their diameter ratio: when the first gear is 3 inches tall, and the second 5, the first has to make 5 cycles for every 3 cycles the second makes.

However, how precise you need to model or otherwise implement gears really depends on the situation. For most games, they're just background details: it doesn't matter too much if they're off a bit. For a gear simulation, it's obviously more important to get them done right.

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