Alpine Community > Building A 'Lift-Bridge Module' for a traction layout


BUILDING A 'LIFT-BRIDGE MODULE' FOR A TRACTION LAYOUT

by George Jones

November 15, 2005

The Southern California Traction Club (SCTC) is an HO scale traction club that operates electric railway vehicles from powered overhead wires. It was formed in 1995 starting with an 'L' shaped Modular layout 22 ft long. The club continued to grow until a 'U' shape was achieved. When the club grew in the year 2000 to the extent that a closed rectangular shaped layout 16 ft by 20 ft became the normal display. This meant that to enter the interior of the display, the members had to crawl (on all fours) under the layout to gain access. Since 75% of the club members are sixty years or older, climbing under the layout was became quite a chore, especially when bringing items along. We had talked about building a 'Lift-Bridge' type module, in which the surface of the module would lift to allow entrance to the interior, but we had done nothing in the way of designing or building it, as none the club members had the necessary metal working skills.

In 2004, while at a train show being held at Ventura, CA, two SCTC members noticed that an Orange County N scale club had a brand new steel framed lift-up section module. Other club members looked the module over closely, and liked what they saw. The club contacted the module builder and contacted with him to construct the framework of such a module. The particular dimensions were chosen, four feet long by 18 inches wide, because the club standard module length is four feet, and we use modules of both one and two foot depth. So this new module ended up as a compromise between a one foot and a two depth. A month later, the club had the steel framework for its 'lift-bridge' module.

The module was made up of five pieces, two black towers of 9x18x35 inches in size. They made out of 1 1/4 inch square thin-wall tubing, welded together with the top plate made out of 2 inch steel angle. It was built about an inch below our standard module height to allow for half inch Homasote plus track and roadbed. On the bottom of each tower were two tapped holes for leveling screws.

The two towers are set up to attach to two white four-foot lengths of 2 x 1 1/2 inch heavy wall steel tubing. Openings had been cut in one tube to allow for easy and tidy passage of necessary electrical wiring.

The silver lift portion is made up of 1 1/4 inch square aluminum tubing, welded together, 18x30 inches in size. On one end of the rectangle, 1 1/2 x1/4x12" long, aluminum flat bar arms have been welded. The arms extend past the of the rectangle eight inches. A 1/2 inch bolt, 1 inch from the end attaches the rectangle to the tower. These long arms allow the lift up panel to clear the track work. On the non-hinge side of the rectangle, there are mounted pieces of aluminum flat bar cut on a 45 degree angle, which aligns and holds the panel as it closes.

The design of the N gauge club lift-bridge allows the club to completely disassemble the unit to move it. But because we are a traction club running under live overhead wire, it was concluded that it would be complicate the interface process if this unit was disassembled and reassembled after each appearance. Since we had an ideal location in one of our club trailers for the entire unit, we are able to transport it intact.

We still had to install a module surface, lay track, including three turnouts and machines, line poles, scenery, structures and overhead wire. For the module surface, it was decided to use 3/8 inch MDO plywood, instead of the half inch Homasote that we use on all our other modules. The use of MDO plywood was chosen provide proper support for mounting trolley line poles and to reduce the problems of warpage that occurs occasionally with homasote.

Examining the surface of the module in the preceding photo, from left to right, you can see a small pedestrian bridge, a two track railway bridge, a power station and twin highway bridges. Another view of the surface is shown below:

Much discussion, engineering and planning went into the building of the overhead wire through the entire 'lift-bridge' module as we wanted to present overhead wire breaks in such a manner that it would look realistic and yet be functional. Overhead wire installation and maintenance in our club is handled by George Huckaby, owner of Custom Traxx and webmaster for www.trolleyville.com. So the job of making overhead wire workable through this module was assigned to him.

On the non-hinge side, (right) he chose brass channeling in place of the trolley wire under both highway bridges. The break in the trolley wire is between the two bridges and is virtually undetectable. The channeling simulates the trolley troughs used in many underpass installations to avoid a dewired trolley shoe or wheel from contacting the steel beams and becoming sufficiently damaged so the car would no longer operate. These trolley wire supports are permanently affixed to the two highway bridges using adjustable screws.

Choosing the size of these troughs was given considerable thought. The trough was to be no wider than the typical trolley shoe or wheel. But what was that? But this sheet was last revised in 1982. Since that time many more prototypical cast shoes and wheels made by different manufacturers such as Car Works, Miniatures by Eric, MTS Imports, Miniatures by Eric and others have begun to be used by the HO traction modelers, especially those who operate from live overhead wires. After much consideration, a section of K&S brass 'C' channel, 1/16" x 1/32" was obtained from a local hobby shop. Initial tests showed that it might work for the range of trolley shoes and wheels currently used by the club and it was used in the module at the overhead wire 'break' points. The blue arrows in the next photo shows the placement and use of these channels.

The hinge side (left) was much more difficult to maintain correct alignment of the overhead wire at the separation joint. A problem we ran into was the swing of the hinge arm. While it lifted the panel up and over the track and over the overhead wire, when the lift-up portion was opened more than 85 degrees, the trolley troughs attached to the railroad bridge that we had built adjacent to the gap, hit the overhead wire on the adjacent module.

We then installed a manual stop to keep the lift section from opening too wide, to protect the overhead wire on the adjacent module. We also added a hold open pin on the inside hinge arm so that the panel can be raised and left open. This is handy while setting up the layout, and other times of non-operation. The previous photo shows the lift section in the raised and locked position.

As we assembled the module we discussed ways of protecting trains from running through an open bridge. The first thing we did was to install a longarm microswitch. when the bridge is lifted an inch, the microswitch fires. This cuts the flow of power to three, two pole, relays. These relays are mounted on the bridge module, and on the modules on each side of the bridge. These relays control the flow of DC power from the A and B throttles to the Atlas block controllers. In short, lifting the bridge cuts track power to 4 3/4 feet of track, on each side of the open space.

A second concern that emerged, was the unauthorized opening of the bridge by a non-club member, such as a viewer wanting to see a train wreck, or by a curious model railroader just looking at the bridge. Since I work in the locksmithing field, I was aware magnetic door locks and access systems. I purchased a Securetron MCL-24 lock. The electromagnet portion was mounted on the non-hinge tower. The armature or steel plate was mounted on the bottom rail of the lift up section.

Power is supplied to the MCL-24 lock by a 24 volt DC plug-in transformer. On the inside and outside of the non-hinge tower. As another safety item, a pilot light that lets club members on the inside of the layout know if the magnetic lock is powered up.

A second advantage to the magnetic lock is that, as the bridge section is lowered the electromagnet pulls the lift-up section down tight, which along with the 45 degree angle flatbar pieces, affixed to the edge of the lift up section and tower, ensures that the tracks are aligned correctly.

The bridge module was first used at the iHobby Expo at the Los Angeles Convention Center in Los Angeles during October 2005. As expected, the module worked fine with no wheels derailing or trolley poles dewiring. All in all the lift up bridge was a great success. No more crawling under the layout, for us age and weight challenged guys.

Look at photo pages for photos of the lift module.

George Jones