A 1/10 scale Chinese south-pointing chariot is for sale via Makers Market:
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.
This model is a 1/10 scale reproduction of the South Pointing Chariot. The completed kit stands 14 inches tall, 14 inches long and 7 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.
It only works (perfectly) on flat land, as long as both wheels remain in contact with the ground.
I posted about this (the south-pointing chariot, not the model) last year, here.
Sort of like intertial navigation, in the way that extreme precision is necessary to avoid error accumulation.