Meccano Differential Analyser
A Differential Analyser is a mechanical analogue computer. It is used
for solving complex mathematical equations involving calculus. An example
would be the acceleration of a car. As the speed increases in metres
per second per second, a graph can be drawn against time on the vertical scale,
which would show a curve. If one wanted to find what distance the car
had travelled in unit time, a complex mathetical formula would be needed
which would constantly sample the speed at frequent intervals and add them
together (integration). The more frequently this occurs, the more accurate
the result. A differential analyser could solve this problem.
The mechanics of a Differential Analyser
The machine essentailly consists of five parts.
1. The integrator. This consists of a disc on which a wheel
at right angles to it is caused to turn. Either the disc can be moved
horizontally under the wheel, or the wheel itself can be moved. There
is a special mathematical relationship between ther two. At least
two such integrators are required to show the principles of the machine, and
often many more are used for complex problems.
2. Torque amplifiers. There must be no slippage between disc and wheel,
and as the wheel itself is required to drive quite complex gearing, some
form of torque amplification is essential. This can be done either
electrically, or through a special torque amplifier mechanism.
Principle of the torque amplifier. The two drums are driven by a
motor in opposite directions. Movement at the input shaft tightens the thread
on the drum, which causes the motor driven output shaft to rotate  thus
amplifying the torque.
3. Complex gearing to link the two integrators and to provide for
adding, subtraction, division and multiplication as required. In order
to function, the gearing must be set up in advance, which is directly analogous
to a computer program.
4. Input table. A stylus must be made to follow a preplotted
curve. The result is mechanically linked to the input drives.
5. Ouput table. This has a similar construction to the input
table, and a pen writes on paper, thus plotting the resultants of the various
mechanical linkages.
This diagram, shows the input table at the top, the various mechanical linkages
and integrators, and the output, thus providing a solution on the output table
shown below.
History.
The first differential analyser was built in the United Sates in 1930 by
Dr Vannever Bush, Vice President of the Massachusetts Institute of Technology.
A machine was then constructed a few years later by Professor Hartree at Manchester
University in England out of Meccano in order to demonstrate its principles
and to obtain funding for a more complex machine. The machine turned out
to be surprisingly accurate and was used to solve quite complex problems
during the second world war. Eventually about 14 machines were built
in the UK. One Meccano machine was bought by Professor Whale and taken
to New Zealand in 1950 and was used for his research at Seagrove Radio Research
Station. It was subsequently used to study river silting, rabbit migration
and at a salt works, and was eventually presented to the Auckland Museum
of Transport and Technology (MOTAT).
The Museum still has the Meccano Differential Analyser. It was the
first analogue computer to be used in New Zealand, and as such has very great
historical interest. It is also a most important part of Meccano History.
The museum plans to put the original machine on display, but it is thought
that that a second machine might have to be constructed with new parts to
demonstrate its operation. William Irwin of the New Zealand Federation
of Meccano Modellers is conducting research into the Differential Analyser,
and can be contacted by email at irwins@ihug.co.nz.
A Meccano Differential Analyser is to be found in the Science Museum in
London.
Meccano Models
Two working models of a differential analyser have been built.
The first was a Morris Maurice Modelplan Meccanomans Club leaflet No. 4. The
second is shown here and was built by Ron Fail to show its essential features.
Tim Robinson has built a torque amplifier which could be used in the machine.
Meccano Differential Analyser built by Ron Fail  from Midlands Meccano
Guild Gazette No 16 April 1993
Further details on this machine will be published as the material becomes
available. Please contact William Irwin if you would like to make a contribution
to his research work.
Michael Adler
Previous page
Home
