Chapter heading

Chapter headingA Compensated Aerial CablewaybyEdward R. Smith

A Compensated Aerial CablewaybyEdward R. Smith

Thepossibilities for practical use as well as novelty for play and experimental purposes make the compensated aerial cableway, shown in the illustrations, not only interesting but also worthy of study. The arrangement assembled in its simplest form with two towers, in thepage plate, shows how the weight of the car is compensated, so that a fairly level course on the track cable is provided. The various positions of the load and cables, showing the application of the compensating principle, are indicated inFigs. 1 to 5, and a multiple system is shown inFig. 6. The details of the constructional parts are also shown. The car may be driven by wind power, as shown inFig. 7, or by a motor, as inFig. 8, in addition to the simple application of hand power suggested in the page plate. Devices for automatically reversing the course of the cars both for the sail rigging and with the use of electrical power, are shown in Figs. 7 and 8. By their use it is unnecessary to have an operator at each end of the cableway. The constructional features were worked out first by experiments on models in a shop, and then applied to a large rigging spanning over 100 ft. between the A-frames. The sketch in the page plate was made from photographs of this construction. Application of the compensating principle to carrying and transportation problems affords opportunity for interesting engineering, in spanning streams, cañons, or gulleys.

In most types of cableways a considerable sag is allowed in the cable supporting the car in addition to that caused by its own weight. Even in systems of practically constant cable tension, in which the wire is stretched by enormous weights, the loaded car causes a sag in the track cable, and ascends and descends an incline when approaching and leaving a tower. The aim in the compensated cableway is to overcome this sag as much as possible, and to offer a minimum of resistance to the car in its course.

The simple form of compensated cableway shown in thepage plateis made by setting up two A-frames, with wire braces supporting them, and mounting the track and traction cables upon them. A light, flexible compensating cable extends from one tower to the other and is fitted to grooved pulley wheels at the tops of the towers, as shown in the detail at the right. The ends of the cable are fixed to wire hooks, from which the track cable is suspended. The latter is anchored at the ends of the wire braces supporting the A-frames. In order to understand the operation of the system it is desirable that the course of a load be traced in its various stages, as indicated in the diagrams, Figs. 1 to 5. For diagrammatic purposes the load is shown passing from the west slope to the east. As the load passes under the first A-frame, as in Fig. 2, the track cable is drawn down at that point; the corresponding end of the compensating cable is also drawn down, raising the opposite end of the track cable, and taking out most of the sag in the center portion of the track cable. As the load passes to the center position, as shown in Fig. 3, the track cable resumes a more nearly horizontal position. When the second A-frame is reached the load draws the corresponding end of the compensating cable down with the track cable, Fig. 4, and the latter assumes its normal position as the load reaches the end of the course. It is evident from the diagrams that the course of the load is more nearly level than it would be if the sagging of the track cable were not counteracted.

For use with a multiple-frame system, the cables are arranged in units between supports, as shown in Fig. 6. The compensating action is similar, the tendency being to level the entire course of the load. The weight of the car and load only is compensated, and since the weight of the cable will cause a sag, the course cannot be level, but may approach this condition.

Fig. 1Fig. 2Fig. 3Fig. 4Fig. 5Fig. 6This Interesting Model Cableway was Built by a Boy for Play and Experimental Purposes: The Principle by Which the Weight of the Car is Compensated in Single and Multiple Systems is Indicated in the Diagrams Above. Cars Propelled by Sail Rigging or by a Small Battery Motor may Also be Used

Fig. 1Fig. 2Fig. 3Fig. 4Fig. 5Fig. 6

This Interesting Model Cableway was Built by a Boy for Play and Experimental Purposes: The Principle by Which the Weight of the Car is Compensated in Single and Multiple Systems is Indicated in the Diagrams Above. Cars Propelled by Sail Rigging or by a Small Battery Motor may Also be Used

A model of the compensated cableway, as shown in thepage plate, or on a smaller scale, may be made by a boy of fair mechanical skill. For experimental purposes the detail may, of course, be refined to a high grade of workmanship, if desired. The size and dimensions of the parts need not be proportioned precisely as shown, but may depend more or less upon the materials available. The track cable should be made of galvanized-iron wire, the compensating cable of fishline, and the towers of 1-in. stuff, the width of the pieces making up the A-frames being increased in proportion to the height. Grooved pulley wheels, set in housings fixed to the top of the A-frames, carry the compensating cable. These may be made of wood, built up in three sections, to provide a flange on each side of the cable groove. The A-frames should be joined strongly at the top, and braced to anchors, sunk into the ground as shown. The hooks from which the track cable is suspended are made of heavy wire, bent so as not to interfere with the H-frame hanger supporting the car, and looped around the cable.

Various types of hangers may be devised to house the two pulley wheels which ride on the track cable. A simple H-frame hanger is shown in the detail sketch in thepage plate. The grooved pulley wheels are set on bolts, and a heavy wire is bent and set through the center block as a support for the car. For experimental purposes, or even for play, when it is not desired to make a more elaborate car, a wooden block or other object of sufficient weight may be used as a load. An interesting feature of the work, especially for a boy, is to devise a realistic coach model, as suggested in the sketch. A wooden block forms the base, and the roof and platforms are made of sheet metal. The windows and doors are painted on the metal. The inventive boy may, of course, build a car with a hollow metal or wooden body, and weight it properly to provide the necessary load.

The motive power is provided by means of a cord, or traction cable, carried around two large grooved pulleys, mounted in supports fixed to the landing stages at each end of the cableway. They are made of wood, a suitable groove being cut around the edge with a saw, and smoothed with a small round file, or sandpaper wrapped over a round rod. The traction pulley is turned by means of a crank, set on the bolt which is used as an axle. The traction cable must be drawn sufficiently taut to provide the necessary pressure on the grooved pulleys, or it will slip. Rosin applied to the pulleys and the cable will tend to prevent this.

Fig. 7The Car is Propelled by the Wind Action on a Sail Controlled Like the Main Sheet of a Sailboat in Tacking. The Trigger Device Releases the Sail, Reversing the Course of the Car

Fig. 7

The Car is Propelled by the Wind Action on a Sail Controlled Like the Main Sheet of a Sailboat in Tacking. The Trigger Device Releases the Sail, Reversing the Course of the Car

If the frames and other fittings have been properly set up, the cableway will support a sail car, shown inFig. 7, or a two-cell electric car, driven by a small motor, as shown inFig. 8. The sailing-car arrangement is often feasible,since a stiff breeze is common in gorges, cañons, narrow valleys, or even in ravines where such a cableway might be set up. The hanger is an H-frame having the grooved pulleys bolted in it, and further reinforced by small blocks at the ends. A braced frame, supporting a deck on which a mast is set, is suspended from the hanger by four curved wires, as shown in the side view, Fig. 7. A sail with boom and gaff is supported by the mast. It is arranged to be shifted around the mast, which is accomplished automatically at the end of a run, or “tack,” by means of the trigger device shown in the top view. The sail is controlled in relation to the wind much as is the main sheet of a sailboat. The car can be operated in this manner only at right angles to the direction of the wind, or nearly so. For play purposes, a boy stationed at each end of the cableway can shift the sail, but the trigger device shown makes this unnecessary. A rubber band is attached to the boom, as indicated in the top view, and a cord and wire are arranged to engage a trigger. A stop for the trigger is fixed to the A-frame so that it is sprung when the car reaches the end of the run. The rubber band reverses the sail, the car having been set on the cable originally so that the forward end is in proper relation to the wind.

Fig. 8The Electric Car Is Self-Contained and may be Reversed Automatically, if the Motor Is of the Reversible Type, by Contact of the Lever with the Stop Fixed to the A-Frame

Fig. 8

The Electric Car Is Self-Contained and may be Reversed Automatically, if the Motor Is of the Reversible Type, by Contact of the Lever with the Stop Fixed to the A-Frame

The electric car is especially interesting in that it provides self-contained motive power by means of a battery of dry cells, and a motor belted to the hanger, as shown inFig. 8. The hanger is of the H-frame type with heavy blocks between the sidepieces to provide for the small grooved driving pulley set on the axle of one of the larger pulleys. A wooden deck, supported by four heavy wires set into the center block of the hanger, carries the motor, and the dry cells are fixed under it. The motor is of the small reversible battery type, and should be provided with a reversing lever. This will make it possible to reverse the car when it reaches the end of its course. The motor and cells should be disposed so as to balance, tests being made for this purpose before setting them in place finally. A cord or small leather belt connects the drive pulley of the motor with the proper pulley on the hanger. These pulleys should be in line, and that on the hanger should be five times the diameter of the one on the motor shaft. The power is shut off at the end of the course by a shut-off switch which strikes a stop crank attached to the A-frame. When the reversing lever and stop are used, the stop crank is unnecessary. A nonreversing motor can be made to drive the car in a reverse direction by removing the belt from the motor pulley and replacing it to make a figure-eight twist.

¶When babbitt metal is heated some of the tin and antimony in it is burned out, making it unsuited for use in machinery bearings, and similar purposes, after several heatings. The oxidation of the metal is indicated by the formation of a scum on the surface.

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