“Perpetual Motion” Machine Makes Novel Window Display (Jul, 1931)

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“Perpetual Motion” Machine Makes Novel Window Display

For novelty in window displays you can’t beat this “perpetual motion machine” as a means of attracting the attention of passers-by. Powered by magnets concealed in the tracks, the steel ball whirls round and round, bewildering those who pause to watch.

SCORES of people will walk right by an artistically decorated store window without giving the display a glance. On the other hand, another store window with a novel display catches the eye of every passer-by.

An unusual novelty, particularly if it is puzzling and mysterious, will attract and hold more attention than a $100,000 painting by a 16th century master.

The reason for the attraction is this: Movement always arrests the eye. Herewith is described a window display novelty which always commands attention. Not only once, but time and again. It consists of a device suggestive of the ever elusive phenomenon: “Perpetual Motion.” Unlike many of the so-called “perpetual motion machines,” it has no gears, belts or levers. It consists simply of a polished steel ball rolling “perpetually” around a circular track.

Suspended above the track is what appears to be a huge permanent magnet, which is for illusory effect only. The device makes a very puzzling illusion. The ball rolls about 30 miles in 24 hours, while an indicator records the mileage. Passers-by will pause time and again to see how many miles the ball has traveled.

Figure 1 gives the general appearance of this device. The tracks are made of %” strips of brass mounted on a circular wooden base 42″ in diameter. A 4-inch steel* ball rolls on the track. The base is mounted on six clear glass bottles which serve, apparently, to insulate the device from the ground. Suspended centrally over the assembly is what appears to be a 30-inch permanent magnet. The ball rolls counter-clockwise around the track about 10 laps a minute. Every turn it trips the level of an indicator which registers the miles covered.

What makes the ball roll? Electro-magnets concealed under the track. How do they get their operating current? Through two bottles rilled with acid solution which makes them conductive. The current is supplied by a six volt storage battery or by a small transformer such as is used for operating electric trains. The metal ball makes electric contacts across the rails in such a manner that the electro-magnet immediately ahead of the ball is always magnetized. As soon as the ball comes over the center of the magnetic field of that magnet, the contact is broken and made again with the next magnet ahead. While the pull of each magnet is very slight, only a very little effort is required to keep the ball moving. If the ball is true, and the tracks smooth and level, practically the only resistance is air friction. Two amperes at six volts will operate the device.

Figs. 3 and 4 illustrate the principal features of the construction. First, a wooden ring 42″ in outer diameter, 4-1/2″ wide, and 3/4″ thick must be made. It is best to build this up of three laminations of 1/4-inch wood. However, various forms of “plaster-board’”

or “wall-board” can be used equally well. The ring is laid off in 40 equal spaces, and 40 rectangular holes 3/4″x2-1/4″ are cut through the ring, as illustrated in Fig. 3.

The electro-magnet assemblies must next be made. Figure 4 shows their construction. The cross-ties, which serve to hold the magnets and the brass rails, are made of wood. Maple is Recommended because it does not split easily. The slots for the rails are cut with a hack-saw blade. The rails should fit tightly in the slots. Note that a 1/4 in. hole is bored vertically through the cross-tie adjacent to the inner rail slot. This is for the purpose of cutting the inner rail with a fretsaw later.

The cores of the electro-magnets can be cut from solid pieces of soft steel, but their magnetic property is improved by making them of laminated construction from 3/32-in. sheet steel. A large number of the pieces can be shaped at once by clamping them in the vise and using a saw, chisel and file. The finished plates are grouped to form the core, and are wrapped with about 100 windings of No. 32 enamel insulated copper wire. One of the ends connects to the inner rail section immediately to the left of the magnet. The other connects to a common return wire to the battery.

After all the magnet assemblies are prepared, they are placed in the holes in the ring base and wired up as shown. The brass strips for the rails are pressed firmly into the slots. Then a fret-saw blade is passed through the vertical holes in the cross-ties, and the inner rail is cut into 40 sections. Each section should be tested for a short circuit. The device is now connected temporarily to the battery, one wire leading to the common return wire, the other to the outer rail. The steel ball is placed on the track and given a little start in a counter-clockwise direction. It keeps on rolling! In fact, it may gain sufficient speed to “jump the track.” A resistance should be installed in the circuit to regulate the speed.

After the tests have proved satisfactory, the rest of the work consists in “dolling up” and camouflaging. A circular, wooden ring 1/4-in. thick is nailed to the bottom to hide the magnets and the wiring. Two brass bolts project slightly from the bottom, to connect with the lead terminals in the corks of the bottles filled with acid solution. Of course, provision will have been made that these bolts connect with the common return wire and with the outer rail respectively, as illustrated in Fig. 2.

The tracks and the magnets are coated heavily with melted paraffin. Then very viscous plaster of paris is poured between the rails. Before setting, this is molded into the form shown in cross-section view in Fig. 2. Afterwards it is well to paint it some dark color. The visible presence of plaster of paris immediately suggests concealment.

Figure 4 shows the construction of the camouflage magnet, and suggests a means of obtaining a true rolling ball. A governor ball from an old steam engine may be picked up at a junk-yard and will serve the purpose very well. The 4-in. dimension is not essential.

The mileage indicator is mostly for psychological effect, but may be dispensed with. Curious passers-by will stop daily to see how many miles the ball has traveled. New signs will greet their eyes. With very little trouble, a mileage indicator from a bicycle can be remodeled to serve the purpose.

This “perpetual motion machine” compels intention. It is an excellent advertising attraction for any store window. Few passers-by are artists; every passer-by is curious.

The device will attract considerable attention to any display or signs set up in your window along with it. While watching the ball their eyes will fall on the signs.

5 comments
  1. Jake Hildebrandt says: May 13, 20097:22 pm

    This is REALLY clever! The sulfuric acid in the bottles is especially brilliant. I think I just may have to recreate this wonderful machine…

  2. Rick Auricchio says: May 13, 20097:55 pm

    Cool! This is like the grand-dad of a stepper motor!

    They don’t really tell how to mix the acid solution, but I suspect modern electronics can provide everything we need without that stuff.

    I’m thinking all that’s needed is a DC power supply with some form of current regulation; should be easy to create that.

  3. Toronto says: May 13, 20099:46 pm

    I thought the purpose of the acid was to make the water conductive, so there were no obvious wires going to the track.

  4. KentD says: May 13, 200910:25 pm

    Yes, the acid is to make the water conductive, and in only 2 of the bottles. I suspect salt would work, or maybe a less dangerous acid. But battery acid would work. The electrodes need to be lead or good stainless steel or they will corrode quickly.
    This is not so much like a stepper motor as it is a linear induction motor, similar to that used in maglev trains, or some amusement park rides. The roller coasters that launch you usually use them.
    The hardest thing to get may be the ball. My local junkyard is all out of steam engine governors. I think it might be best to find the largest steel bar you can find and scale the rest to that size. If you can find a ball the right size, you could use HO scale track. Use surplus solenoids for the magnets.

  5. Rick Auricchio says: May 14, 200912:53 am

    Ah, thanks, Kent. I didn’t realize the visual effect of the bottles as supports without visible connections.

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