The deck on top of which the track runs consists of three principal items – the lift bridge and two “wings” that are on either side of the of the bridge and which adjoin adjacent modules in the same way as any other Free-mo module. The deck and each of the wings are 13½ inches wide. Being double track to Free-mo specifications, each track is just over 5 inches from each edge (the Free-mo standard being at least 4 inches). The deck could have been made a full 26 inches wide which is the Free-mo standard for a double-track module but operating a much heavier bridge not to mention packing and transporting a much heavier design would have been a challenge.
The wings are built to Free-mo standards, with ¾ inch plywood where the module joins adjacent modules and ½ inch plywood sides. Under each wing is a turnbuckle with is used to raise or lower the wing to make it horizontal.
I shall refer to the “hinge end” and the “open-close end” to distinguish between the ends of the bridge and their operation. The bridge deck is made from ½ inch plywood braced with 1x3 dimensional lumber sides.
The bridge is fastened at the hinge end with two European-style articulated cabinet hinges that move the bridge away from its adjacent end to avoid binding or breaking of the rails where they meet. In addition, there are two friction devices that I found in area of The Home Depot where they sell cabinet hardware. The amount of friction is adjustable. These help to ensure that the bridge stays up when in the upright position and, when lowered, provides resistance the chance of it slamming shut if the operator is inattentive.
The portion of the deck bearing the track has a cut-out to amplify the safety effect of the hinges with respect to the track. This cut-out also serves an important role in activating a U-shaped home-made rocker actuator which controls track power and the activation of safety gates when the bridge is lifted.
The open-close end of the bridge has two important features that ensure perfect track alignment when the bridge is closed. The first of these is tab/notch that is slightly wider than the combined width of both tracks. The end of the tab is filed to a slight angle so that, when the towers are properly aligned to ensure a snug but not tight or loose fit of the bridge, the bridge slides into place snugly. In addition, there are two small adjustable rests on the outer edges of the open-close end of the bridge. These allow for fine-tuning of the horizontal alignment of the open-close end of the bridge.
When the bridge is lifted the cut-out beneath the track at the hinge end drops beneath the horizontal plane of the deck and causes the U-shaped home-made rocker switch to move. This rocker actuator is made from layers of styrene laminated to a thickness of approximately ½ inch. Its purpose is to open and close small micro-switches that have two distinct purposes. The rocker actuator is fastened to a pivot located at its mid-point and is sprung with a coil spring, supplemented by a rubber band so that once the “U” moves past its mid-point it will snap to the other side of its travel. I recall one of my childhood homes having a similar-looking spring latch which snapped shut to hold the old-fashioned wooden storm door closed.
I used three micro switches, one triggered/released by one side of the rocker actuator and two by the other side. These micro switches are of the double pole-single throw variety. These are readily available from Mouser or Digi-key (see my Links I Like page).
The single switch serves to turn track power on when the bridge is lowered and turns it off when raised.
The two switches on the other side serve to operate two Tortoise by Circuitron (“Tortoise”) switch machines that have been re-engineered to form physical barriers to prevent rolling stock from hitting the floor when the bridge is raised – more about that later. These two switches are bolted together using the two holes already drilled in the switches (many switches of this variety seem to be made with two built-in holes). Of course, when two double pole-single throw switches are mounted together they turn into a double pole-double throw switch (I tried to find purpose-built micro switches of the double pole-double throw variety but without success).
The double pole-double throw micro switch is wired in the same way that one would wire a DPDT toggle switch to change track polarity on a reversing track before the days of automated reversing track DCC circuit boards. When the rocker actuator presses against both micro switches at the same time a 12-volt DC current flows in one direction to each of the Tortoise barriers. When the rocker actuator releases both micro switches at the same time the DC current flow reverses and the Tortoise barriers move to their opposing position.
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| fully open position; note yellow Anderson power poles disconnected (reason to be discussed in a later post) |
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| different angle |
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| my home-made rocker engaging the double pole double throw switch |
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| the rocker part way back to the other side (DPDT switch no longer engaged) |
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| close up of hinges and friction devices |
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| close up of friction devices |
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| notches at both ends help guide the bridge into precise alignment with track; the white physical barriers will be covered in more detail in a later post |
To be continued...
