Science museums all used to have displays of
mechanisms similar to the ones in the clock. They were considered
essential for training Ďmechanicsí and the models are obviously easier
to understand than drawings. They disappeared because the rise of
computers led to mechanical ingenuity being replaced with simpler
mechanisms controlled by clever software. One of many examples is the
sewing machine. These used to have elaborate mechanical cam systems to
create fancy stitches, and now have computer controlled stepper motors
Even before the rise of computers, Iím not
convinced the displays of mechanisms were ever that practical because
always Ďthe devil is in the detailí. Some mechanisms only work on a
small scale with tiny loads. Some need making really accurately. Some need
really low friction bearings. Some transfer power ridiculously
inefficiently. Some are only intellectual curiosities without any
practical application. Choosing a mechanism for a particular application
depends on so many factors the models donít show. Useful or not, they
certainly are part of the history of teaching mechanics, and they are also
just fun to watch and to play with.
This is a useful alternative to a crank. Making an
accurate crankshaft, like in an internal combustion engine, is difficult
and takes time. A row of eccentrics is easier to make because they can
have a single main shaft running through the middle.
This is usually used to convert linear motion into
rotary. It was historically important on early steam engines.
This is one of Paul Spoonerís mechanisms that he
uses on his automata. Iíve never come across any industrial uses for it.
Ratchets are widely used, for example on winches and
clocks. However I had never come across one in which the ratchet arm moves
the wheel forward when it is rocking both clockwise or anticlockwise.
A Geneva is a mechanism that converts a constant
motion into intermittent motion. This one is sometimes used on electric
clocks that advance the hands once a minute.
Paul found this in a book of ĎIngenious
Mechanismsí. I suspect it was always more of an intellectual puzzle than
for any practical application.
Cams are widely used, for example for lifting the
valves in internal combustion engines. Complex cams were also common in
printing presses and industrial machinery. The cam follower needs to have
low friction for a cam mechanism to transmit much power.
This is used in reverse on industrial riveting tools,
a long easy pull creating a powerful short pull on the rivet. It is not an
efficient mechanism as there are so many bearings.
Low pressure air, as pushed out by the bellows, is
used to power amazingly complicated mechanisms on player pianos. Paul also
uses it on his automata. I had never tried it before but was amazed how
much force it can exert.
This is a mechanism that used to be in Chicagoís
science museum, copied from a photo online. I was curious to see it work,
but donít know anything else about it.
QUICK RETURN CRANK
Both Paul and I use this mechanism sometimes to move
automata characters. Itís easy to make.
This can produce a bewildering array of different
movements, by moving the position of the teeth of one gear relative to the
teeth in the other. Iíve never come across any practical applications.