and turntable is often the main focus point of a layout. Modelers build
their own roundhouses yet few attempt to build their turntable. This is due
to several factors but mostly to the complexity and precision required to
create a rotating bridge that turns smoothly and lines rails up accurately
are only a relatively few tables on the market today. One or two small
tables are available but are not realistic and do not meet the needs of
most modelers. Most commercial tables of any reasonable size are
expensive, hard to find, have few features, and are difficult to use. Most
are positioned by eye which can be a slow and tedious process. Those that
are automatically indexed reliably are rare and expensive.
This project is
based on a design built 35 years ago. It takes a new look at an old
problem and provides what seem to be a few unique improvements to the
situation. First and foremost, positioning is done optically using a light
source and pairs of photo cells. This principle is used today in precision
machines used to manufacture parts to close tolerances measured in
millionths of inches.
improvement is the use of a printed circuit board (PCB) for the "slip
rings" used to transfer power to the bridge rails instead of depending
on the ring rail. This PCB is also used to replace the various switches
usually required to control the power to the approach and stall tracks as
well as to provide power to the light source for the positioning system.
This makes operation much easier and less confusing.
improvements include details in the pit construction not included in
models I have seen including a pocket in the pit wall for the maintenance
of the motor and boogies at the bridge ends. Also modeled is a simulated
locking system to keep rails aligned.