Meccano Babbage Differential Calculator

A Meccano model was published in Constructor Quarterly in March 2005 called a Difference Engine and was designed by Tim Robinson. The Babbage machine is one of the icons of the pre-history of computing. The original can be seen in the Science Museum, London.

In 1790, a Frenchman called Baron Gaspard de Prony produced 18 volumes of logarithms and manuscripts calculated to between 14 and 29 decimal places. It was a huge job of work in those days. Babbage in 1832 realised that the work could be partly done on a machine which could automate simple calculations. It calculates the Difference between successive pairs of numbers squared and this is nothing more than simple addition. The 'Method of Differences' is a technique for calculating tables, in which the vast majority of the calculations involve nothing more than simple addition or subtraction. So he built a mechanical adding machine. To work successfully, it must not only add, but carry into the next digit.

Tim's machine is a huge project in Meccano because each stage is complex and the stages are repeated 13 times. The machine is hand cranked, and produces results depending on the initial number settings.

The mechanisms are quite complex and difficult to understand. It is only when the model is built and adjusted that its complexities can be appreciated. It is for this reason that a simple model has been built using only a few cages, which entirely and faithfully reproduces Tim's mechanisms, but avoids repeated cage building which is very costly in parts and is the minimum required to understand the principles on which it works.