O Scale Trains Magazine Online

the track power to the turntable. It has
two short insulated sections that allow the
polarity of the turntable to be switched at
each 180 degrees of rotation. The circle
of N Scale track provides power to the
lights on the turntable.
The square driving post also has a 1/8”
center hole for the center alignment pin.
It is attached to the drive disc with two
woodscrews. The sides of the post were
carefully sanded to allow a close fit into
the turntable. We’ll see more on that
later.
The disc has routed slots that hold
the wires feeding the two track circles.
The wires exit the top of the disc against
opposing flat sides of the drive post. This
insures that they will clear the center hole
of the pit as the post rotates. Miniature
connectors provide quick electrical connections
to the turntable.
Three-rail locomotive pickups provide
the voltage transfer to the power tracks.
The voltage pickups for the N Scale track
are installed 180 degrees apart. They are
mounted on brass strips.
The two pickups for the turntable
power are mounted in one cutout. This
is due to the short length of the two insulated
sections of the track circle. Their
mounting brackets were made from 3/8”
square styrene tubing.
The motor is a Pittman gear-head
motor with a 19.5:1 speed reduction. The
motor mounting bracket is a piece of 3/4”
plywood drilled to fit the body of the
motor. The bracket was then cut down so
the hole was open on one side. A metal
strip is used as the motor clamp. A rubber
bushing on the motor shaft provides
the friction-drive transfer to the cork drive
ring on the disc. Since the output shaft
of the motor is off-center, rotating the
motor in the mounting bracket adjusts the
load of the bushing on the drive ring. The
weight of the drive disc helps maintain
this friction coupling.
The photo above shows the drive disc
installed into the drive box. Masking tape
was added over the wire slots on the disc
to hold the wires in place. The drive disc
is shown rotated with the insulated sec-
tions of the HO power track positioned
over the power pickups. Positioning the
drive block at this location will orient the
turntable at approximately 90 degrees to
the inbound track. This will be the point
of rotation at which the turntable track
polarity will be reversed. The drywall
screws located around the drive disc add
extra support to the top panel of the drive
box,
The photo above shows a bottom
view of the assembled drive box. The
motor mounting clamp is accessible for
adjusting the drive bushing load on the
drive ring. The power pickups can also
be adjusted, if necessary, from under the
layout. The track and lighting wires are
secured with nylon cable clamps.
The top panel of the drive box is 1/4”
plywood, and is attached to the sidewalls
with drywall screws. The center hole is
two inches in diameter. The corners were
cut out to clear the corner posts. The
cutout sections were glued to the lower
side of the corners of the base. These feet
allow clearance for the wiring, when the
drive box is sitting on the workbench.
The 2” x 2”corner posts are 2-3/8” high.
A 5/16” diameter hole was drilled through
the posts, base, and corner feet. The drive
box is mounted to the layout by four 1/4”
diameter bolts through these holes. A sixscrew
barrier terminal strip provides connections
to the power supply and control
panel.
A 28” diameter circle was drawn on
the top panel of the drive box, which
established the location of the outer side
of the pit wall. A 1-7/8” wide strip was
cut from a large sheet of 1/8” styrene
on a tablesaw. This strip was then cut to
a 90” length. The cut edges were then
sanded. A heavy bead of adhesive chalk
Nov/Dec ’06 - O Scale Trains • 1