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Here's a reliable scheme for controlling unmodified switch points with
pneumatics. This scheme is for use on track that is raised up off the baseplate
in modules. I have reduced the depth required below the track to a minimum of 9
plates in the second prototype. It was 12 in the first one.
The system mimimises the profile above ground level for best aesthetics and
allows longer train vehicles to overhang the lever frame.
The first picture http://www.brickshelf.com/cgi-bin/gallery.cgi?i=1436719 shows
two switch points set straight. On the right is the first prototype, which uses
2 pneumatic cylinders with nozzles facing downwards. Only the nozzles at the
bottom of each cylinder are used, so that leaks from the top of the cylinder
cannot interfere with reliability. The aim is that the system will work
perfectly for at least a day's continuous operation at an exhibition. On the
left is the ballasted second prototype, which uses 2 cylinders but on their
sides. This reduces vulnerability of nozzles and saves 3 plates height. Both
points have a signal take-off, which is intended to pull a flex rod downwards on
a signal post when the points are set curved.
The second picture http://www.brickshelf.com/cgi-bin/gallery.cgi?i=1436717 shows
the two points set curved, and is a close-up. Notice that the second prototype
uses a 5L liftarm above ground to the first prototype's 7L one, and that the
profile is lower.
The third picture http://www.brickshelf.com/cgi-bin/gallery.cgi?i=1436721 shows
the underside. The first prototype is above the second. The green 1x2 bricks
with cross hole on the first prototype stop the cylinders moving downwards. On
the second prototype the grey axle cross connectors hold the cylinders in place.
The dark grey liftarm between the beams holds them together and a black 1x2
brick with 2 holes holds the 4L thin liftarm slider that prevents downward
movement. This is necessary because of the offset between the cylinders and the
load (the 5L liftarm above ground pushing the lever slider of the switch point).
Vertical bracing of the beams was not necessary, proved by testing.
Notice that the pneumatic hoses use 2cm of rubber hose and longer flex tubes.
This keeps the balloon effect to a minimum, maximising reliability and
minimising the required and wasted air power, which is especially important
because the switch point could be some distance from the control panel. From
here to the panel I will use more flex tubes and very short rubber hoses to
connect them together. With the hoses as shown, the switch point will change to
straight with one pump of a pump clinder or will switch to curved with 2 pumps
of a pump cylinder. I suggest that 1 pump is required for every 10cm of flex
tube, but this would probably be double for rubber hose.
My next development will be to put the second prototype into a scenic railway
layout module like this one:
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=1150115 for further testing.
For a layout with raised track, this system has the advantage of a limited
linear actuator doing a limited linear task, so there are no requirements for
torque clutches on gearmotors. It also has a lower profile above ground than a
gearmotor system or my micro motor system and less depth below the track than a
buried gearmotor system. It requires no modifications to switch points and
avoids using the top cylinder nozzles so it should be more reliable in the long
term (I had one modified micro motor-driven switch point come unstuck after 3
years), retaining the advantage of the built-in positive location of the switch
point slider.
PLMKWYT
Mark
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