Dr. Wan's Drawing of the South Pointing Chariot

(Found at http://www.suelab.nuem.nagoya~u.ac.jp/~suematsu/navigator/wan.html)
 

Approximative translation of the Japanese Inscription:

The following restauration plan was drawn by Dr. Wan from China. A full size model was built from his blueprint and can be seen in the Chinese Historical Museum in Beijing.

This is how it works: The rear end of the draught pole is connected to two small cogwheels by a line, or cord. When the chariot turns right (the pole is drawn to the right side), the pole swivels in its bearing and the rear end moves to the left side. The cord on the left hand side becomes slack and the small cogwheel on this side is lowered by its own weight, meshing with the big cogwheel in the middle and the left roadwheel's cogwheel at the same time. By the movement of the chariot the big cogwheel will now be turned in the opposite direction, moving relative to the pole und thus pulling the small cogwheel out of engagement again by means of the cord's tension. The wooden statue serving as pointer is fixed to the big cogwheel and will always point into the same direction (south, if set so in the beginning), no matter which direction the chariot is turned.

The cord needs to be adjusted so that the two small cogwheels do not touch any other cogwheel during straight running of the chariot.
 
 

Back View..

..Side View..

..and Top View

Some of the above drawings are reproduced in Joseph Needhams's book also, plus this photograph of Wang Chen-To's working model (Note: The large gear-wheel is removed to show the cables and poles more clearly)