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Doc's Classic Period #4 Traveling Jib Crane

Hi folks, Doc here, with another model from the Classic Period of Erector - the #4 Traveling Jib Crane. The illustration for this model in the #7 Manual caught my eye; it was a simple, straightforward design, and I liked the look of it. I also found it to be a design that was easily adaptable, so I came up with a variation of my own (more on that below). But, the best part of the model is the motor assembly: it features both a gear release and a brake! I'll describe these in some detail later. Construction is very basic, as you can see. The framework is composed entirely of B and C girders, 11, 21, and 41-hole strips, and N long double angles. The long crane boom is fixed at a specific angle, and the motor simply raises the "load".

Let's focus on the motor assembly: This model uses the "No. 13 - 4's" configuration, a slow-speed, heavy load hoisting unit powered by a P-58 battery operated motor. A combination of P13, P49 and CJ 36-tooth gears drive the shaft on which the lifting cable is wound.

Refer to the photo above: The gear release is a horizontal lever on the side of the motor assembly made from 2 11-hole strips bolted together; this lever is free to pivot at its center (Point #1). When the back end of the lever is moved to the right, the front end of the lever moves to the left; when it does, it pulls the main drive shaft to the left along with it. This serves to disengage the forward CJ gear from the P13 gear on the rear shaft (Point #2). This effectively puts the motor assembly into "neutral." Moving the lever back to the left re-engages the drive gears (see Inset below).

The brake "lever" is 6" axle attached to the side of the motor assembly beneath the gear release. It pivots at the front on a P37 collar. A short length of string is tied to the collar; it passes up and over a P7 pulley on the end of the drive shaft, then back down to the axle where it is tied off. When the motor is under power and the drive shaft is disengaged using the gear release lever, any load on the lifting hook will fall under its own weight. Pushing down on the back end of the brake lever tightens the string around the P7 pulley, causing the motor drive shaft to stop turning, stopping the falling load at the desired height. Very clever!

  

My variation on this model involves removing the P17 spoked wheels and mounting the entire assembly on a railroad flat car. To increase the maneuverability of the crane, I put a swivel assembly made from BT turret plates between the crane and the flat car. Although the crane boom is still fixed, the whole assembly can now rotate 360º.