Noel C Ta'Bois' Exceptions

All designs for South Pointig Chariots based on the work of Mr. Lanchester so far have one feature in common: The basic dimensions for track and roadwheel diameter had to be the same. Why this ? Consider one wheel fixed at its point of contact to the ground. If the chariot is turned round one full circle, the other wheel will have traveled a distance of 2*p*track (circumference of the circle round the fixed point on the other wheel). If the circumference of the moving wheel is the SAME - namely p*diameter -, it will have rotated exactly once round its shaft. Using identical gearwheels in any number will turn the pointer exactly once too - goal accomplished !

But what if for some reason this ratio has to be avoided ? Well, if the wheels have half the diameter, we have to gear up by a factor of two. This nice little model of Mr. John Nuttall speaks for itself. The only parts fixed to the horizontal shaft are the endcaps and the two columns carrying the small contrates. (Click here for a "modernized" version of this design, realized by Richard Egge, or here for the "classic" realization of Graham Jost from Australia, or here for a LEGO realization, but be sure not to miss the math details !)

Of course the same holds true if we want to use double sized roadwheels:

And now for the not-so-flat regions of our planet: Unequal sized wheels. Here the gearing has to be tailored to the individual wheels (to be seen on the vertical shafts).

Source: The Meccano Magazine, October 1979, pages 129ff