Deborah R. Fowler
Gear Ratio
Posted on June 22 2013
Updated on Nov 25 2017
Looking at the wiki entry for gear ratio, it seems quite complex, however here is a simplified version.
Gear ratio is the number of revolutions from one gear to the next. It depends on the number of teeth.
For example,
These gears each have differing angular velocity.
For example, if implemented in Houdini, the red gear could be rotating at say -$F (frames per second), call this the rotateRedGear
Then the green gear next to it, with 8 teeth, would rotate at a rate of -ch("../rotateRedGear/rz") * 12 / 8
Then the blue gear next to that one, with 6 teeth would rotate at a rate of -ch("../rotateGreenGear/rz") * 8 / 6
Here is the hip file if you want to experiment.
This is true for other configurations of gears:
