Prof. M. A. Chaves' Meccano Chinese Chariot

Designed more than fourty years ago (i.e. in the late '50s), this model is interesting in that it features only one differential á la Lanchester but nevertheless keeps a remarkable low center of gravity. This is reached by putting the differential's working shaft parallel and even below the wheels' axle. Trade off is a third parallel shaft and a 90 deg bevel set to mount the pointer at the required place.

Gear trains		= denotes "fixed to each other"
Right road wheel to differential (3 is needed to make 5 and d rotate in opposite directions)		1=2,3,4= 5
Left road wheel to differential		a=b,c=d
Differential (cross shaft A is fixed to first parallel shaft) to pointer		A=B,C=D, E

Regarding gear sizes, do the following "Gedankenexperiment": Keep road wheel 1 fixed to the ground and its axle; then move chariot through one full turn. Wheel E has to turn one full cycle and road wheel a will turn

(1) phi(a) = 360° * (E : D) * (C : B) * 2 * (c : b)

During the experiment the tire of a rolled a distance determined by track t and wheel diameter w:

(2) 2 * t * PI = w * PI * phi(a) : 360°

Putting all together, we get:

(3) t = w * (E : D) * (C : B) * (c : b) and (c : b) = (4 : 2)

pictures taken from http://www.fc.up.pt/mp/machaves/Meccano