Vintage film explaining how a differential gear works

This film does an admirable job of clearly explaining what can be a rather confusing mechanical concept -- the differential gear. It's Tuesday, and you owe it to yourself to learn a little something. If you already know how a differential gear works, I'm sure you'll also enjoy the charming retro qualities of this film!

True, we normally hear differentials in cars, but they've had other some intriguing uses in the past. Take for example the amazing South-pointing chariots created in ancient China. A carved wooden figure standing in a horse-drawn chariot would point South no matter which way the cart turned or how often. This was done with a differential.

Here is where you can get a wooden South-pointing chariot kit!

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Wooden Chinese South-pointing chariot kit

Some time ago, I posted about the ancient Chinese mechanical marvel that is the South-pointing chariot. I followed up a year later with some video of a working model of the South-pointing Chariot. It's an incredible invention. Whichever way the figure on top was set initially -- usually pointing toward the imperial city -- it would continue to point that way regardless of where the chariot was pulled. It wasn't done with a magnetic compass. In reality, is was a very early (probably the first) example of differential gearing in history.

Given its rich history and marvelous design, I was thrilled to find this the other day: The Ma Jun Navigation Chariot kit, a 1/10th scale working model of the South-pointing chariot.

More about the South-pointing chariot kit:

Invented in 225 A.D. by mechanical engineer Ma Jun during the Three Kingdoms period, the chariot's differential gearing system provided solitary cardinal direction centuries before the magnetic compass. Romantically known as the "South Pointing Chariot," it is considered by antiquarians as one of Ancient China's most complex inventions, yet it's dragon finial will point in any direction to which it is initially oriented. Made from poplar, the kit's 37 pieces snap out from three backing boards. Detailed written instructions guides builders through construction with clear pictures.

The kit is made of Poplar -- a clear grained, fairly soft wood that is easy to sand and finish. To make the kit you will need some basic woodworking tools: a utility knife, a flat and round file, sandpaper, wood glue, and clamps. If you're looking for a place to get this stuff (or anything else), Woodcraft has it all! Highly recommended.

Here is where you can order the The Ma Jun Navigation Chariot.

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