Connecticut River Drawbridge Module.

Drawbridge Modules
MPRR Clinic Night Archive

Clinic Photo Gallery

The CT River Drawbridge Module Under Construction.

Above: A view of the under construction Connecticut River Drawbridge module back in September 2000. Photo Credit: Jim Spavins

Drawbridge Pivot Point.

Above: The pivot point on the Connecticut River Drawbridge module. Photo Credit: Jim Spavins

Drawbridged Removed.

Above: The drawbridge removed and ready for transport. Photo Credit: Jim Spavins

Drawbridge Plug.

Above: The plug on the underside of the bridge carrying power to the motor. Photo Credit: Jim Spavins

Clinic By: Jim Spavins
Clinic Night Date: September 24, 2000

Back on Sunday, September 24, 2000, club member Jim Spavins presented some tips for building model drawbridges.  He brought along his then, under construction Connecticut River Drawbridge module.  Below is an article which was written several years after the clinic.

Drawbridges and modules are made to go together.  Animation on modules generally draws a crowd at a train show and drawbridges are one way to capture attention.  However, building a drawbridge for a module offers a unique set of challenges.

The module discussed in this article is the second drawbridge I built for a module and allowed me to implement some lessons learned from the first module.  This module features a prototype bridge between Old Lyme and Old Saybrook, CT.  There were many factors involved in the initial design process that affected the overall design of the bridge.  The three of most concern were the cost, the size of the finished bridge, and how easily it could be moved once completed.

At the time when the module was constructed I was a high school student.  I didn’t have large sums of money to spend or an unlimited amount of time. This quickly ruled out scratchbuilding and using many of the more expensive bridge kits on the market. I settled on using the Walthers’ Double Track Truss Bridge kit as a base for the kitbashing efforts on the project.

Choosing this kit had many advantages in that it was fairly easy to modify, fairly rugged, and most important, available at a reasonable cost. In addition, the kit offered some inherent strength by its own design which is important to make sure the finished module is durable enough to withstand being moved from train show to train show.

Of course, as with any prototype-modeling project, a fair amount of selective compression would be in order. Since the drawbridge was going on a four foot module, I needed to selectively compress the bridge from the prototypes ten sections down to four. If I had the ability to transport a longer module, I may have been able to bump up the overall size and add more sections. However, by painting the bridge the same colors and placing the bridge in the appropriate setting, the finished bridge is easily recognizable by those who know the area.

Since the bridge was going on a module, I needed to be able to move it safely, as well as quickly and easily. Many design choices need to be made because of this design requirement. First, I needed to be able to take all of the sections of the bridge off the module during transportation. By drilling holes in the piers and abutments, and adding a short section of brass rod to the underside of the bridge, I ensured that the bridge would line up in the same spot every time.

Second, I needed a simple mechanical system to raise and lower the bridge. Even though the prototype Connecticut River Draw is a rolling bascule type drawbridge, I opted for simpler static pivot point to offer a way for the center span to raise and lower. Instead of rolling back, the model bridge turns on a single fixed point.  While not the best arrangement in terms of appearance, it still draws a crowd at a show.  One of the reasons for this compromise is that many times in the rush and confusion of setting up or taking down layouts at shows, things get broken. A rolling bascule bridge - with its more complicated gearing needs were to break, the module could be out of service for a show.  It would be nice to design a system that would allow the bridge to roll in a prototype manner, but after having built a few of these drawbridges, it would add a substantial level of difficulty to execute the full rolling bascule mechanism.

Finally, getting power to the tracks is accomplished through the use of plugs built into the base of the bridge and the piers.  This allows solid connections to the mainline feeders and doesn't rely of rail joiners to conduct power.

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