Evolution of an Erector Model: The Walking Beam Engine

Hi folks, Doc here. Welcome to the first installment of a new feature of the Model Gallery: "The Evolution of an Erector Model". Of all the wonderful model designs that have appeared in Erector manuals over the years, I'll bet that each of us has a favorite, or at least a favorite type. I'm sure that Gilbert did, as there are a number of models which show up again and again in different incarnations. My own favorites were always the big, "industrial" type designs: they look great and typically feature plenty of great action. A prime example is the Renaissance Period Giant Power Plant. Another design of this type is the subject of this installment: the Walking Beam Engine (WBE).

A WBE is named for the elongated double-ended arm assembly, or beam, which pivots at its center and typically connects a motor-driven flywheel at one end of the machine to a piston at the other end. An eccentric cog connects the flywheel to the beam. As the flywheel rotates, the cog causes the end of the beam to rock up and down like a teeter-totter, or "walk", thus giving the machine its name. The other end of this "walking beam" drives the piston(s). All Erector WBEs share these attributes in one form or another.

At least one version of WBE was featured in Erector manuals during every model year from the mid-20s up until the end of Gilbert Erector production in 1962. The first WBE to appear was a large but rather haphazard design, looking not unlike an old fashioned spinning wheel.

As seen in Figures 1 and 2, it consists of a tall, rectangular framework made from "angle" girders (2 B or C girders screwed together using CH angles). The "walking beam" itself sits atop the framework, while the large spoked flywheel hangs off one side of the frame near the end. The piston assembly sits atop a small platform located on the ground under the framework. A P58 motor, also sitting on the ground, drives the flywheel via a string and pulleys. A "governor" assembly atop the piston platform is also driven by a string and pulleys. Overall, this is not a bad looking model, but the design is very inefficient from a space standpoint. The flywheel is hung way out on an upper corner of the large framework, which must be screwed to a wooden base of some kind, along with the motor piston/governor assembly, which are loosely arranged to fill up the enormous empty space beneath the framework.

A second version of WBE, seen in Figure 3, also appeared in Erector manuals in the 1920's. At first glance, Figures 1 and 3 appear to be front and back views of the same model. Upon closer inspection, however, several differences can be seen. The framework and walking beam in the second model are built with square girders rather than angle girders. Even the large flywheel is "double strength" in this version, being composed of a pair of spoked rings mated together using small double angles. Most noticeably, the motor has been relocated and now drives the flywheel using gears and ladder chain rather than pulleys and string. In keeping with these modifications, a freestanding tower has been added to the exposed side of the flywheel to support its extra weight, as well as the weight of the chain. Finally, the governor and its platform have been modified from the original design.

A third and final WBE design appeared during the same period, and it made up for the shortcomings of the first two in a big way. Figure 4 shows an original manual illustration of what I consider to be finest WBE design of them all. It is big, beautiful, and elegant, and not surprisingly could only be built with the famous #10 set, unless you happended to own a sufficient number of extra parts.

As shown in the illustration, this enhanced version has a very balanced, symmetrical design, with little wasted space. It sits on (and within) its own large, sturdy base constructed primarily from large base plates. The walking beam is supported by an elegantly designed tower which is located near the center of the raised base unit. The standard boiler/piston assembly sits at one end of the base, while a pair of heavy but smaller flywheels occupy the other end, their lower portions recessed into openings in the top of the base unit. The flywheels are made from CS wheel segments and I 21-hole strips. This double-flywheel design enables the tower to be placed, in effect, between the flywheels at the center of the platform, adding to the lower profile and balanced appearnace of this version of the WBE. A P56-G motor sits in a well beneath the beam tower and drives one of the flywheels using a pulley and string.

By the 1930s, a smaller version of WBE appeared in Erector manuals (Figure 5). This was the first WBE that could be built with the smaller (lower-numbered) motorized sets.

This design was really a scaled-down version of the large, double-flywheel design shown in Figure 4. Still powered by a P56-G motor, its flywheels were now no more than 3" MH disk wheels. By the 1940's, this design had evolved into a slightly modified design shown in Figure 6. Now powered by the famous A49 Electric Engine and sporting a raised base and control building, the new design still retained many of the characteristics of its predecessor.

During this same period, Erector manuals began to feature a new "large" WBE model (Figure 7). Like its large, 1930's counterpart, it had an attractive, elegant, and symmetrical design. However, it put a new spin on things by featuring a twin-walking beam/single flywheel configuration rather than the single-beam/double flywheel configuration of the earlier version. It also went back to the beginning of Erector WBEs by borrowing the large flywheel design of the original 1920's "spinning wheel" design (Figure 1). This version is a close second on my list of best WBEs. It is a fun model to build and runs smoothly and has great action, making it an impressive display piece when completed. A pictorial of this version along with several others are currently available in the Model Gallery.

A final version of WBE appeared in Erector manuals in the final years of Erector production. It was the smallest and simplest design of them all, and rightly so, as it was powered by the anemic 3-volt DC-3 motor. Once again, MH disk wheels functioned as flywheels, but gone was the traditional T boiler as the piston; instead, an MC 2½" base plate served that function. Oddly, this model could only be built with two sets, the "Motorized", or "Automatic Radar Scope" set ( a smaller set), or the largest of them all, the "Master Builder" set (!?).