Chapter 10 gear VẼ CƠ KHÍ

GEAR The south-pointing chariot (or carriage) was an ancient Chinese two-wheeled vehicle that carried a movable pointer to indicate the south, no matter how the chariot turned Usually, the pointer took the form of a doll or figure with an outstretched arm The chariot was supposedly used as a compass for  navigation, and may also have had other purposes There are legends of earlier south-pointing chariots, but the first reliably documented one was created by Ma Jun (c 200–265 CE Common Era) of Cao Wei  during the Three Kingdoms, about eight hundred years before the first navigational use of a magnetic compass No ancient chariots still exist, but many extant ancient Chinese texts mention them, saying they were used intermittently until about 1300 CE Some include information about their inner components and workings There were probably several types of south-pointing chariot which worked differently In most or all of them, the rotating road wheels mechanically operated a geared mechanism to keep the pointer aimed correctly The mechanism had no magnets and did not automatically detect which direction was south The pointer was aimed southward by hand at the start of a journey Subsequently, whenever the chariot turned, the mechanism rotated the pointer relative to the body of the chariot to counteract the turn and keep the pointer aiming in a constant direction, to the south Thus the mechanism did a kind of directional dead reckoning, which is inherently prone to cumulative errors and uncertainties Some chariots' mechanisms may have had differential gears If so, it was probably the first use of differentials anywhere in the world Do you know how a differential works? Would you believe that the Chinese invented one nearly three thousand years ago, and used it as a non-magnetic compass to keep track of north and south as they traveled?  The figure on top of this amazing machine maintains its orientation no matter which way the chariot is pulled, pushed, turned or even how fast How it does this is via a clever application of gears and mathematical ratios that would have earned the awe and admiration of Pythagoras, Euclid and Aristotle themselves.  It took us exactly eight prototypes to get the gearing worked out properly a fortuitous number, since eight is also the luckiest number in Chinese traditions his model is a 1/10 scale reproduction of the South Pointing Chariot The completed kit stands 14 inches tall, 14 inches long and inches wide It contains over 37 precision cut hardwood pieces (not including the gear teeth), and when properly constructed, it really works!  Examples of the South Pointing Chariot can be found in fine museums all over the world, and now you can have your own museum quality model for your personal display of ancient technology.