What Makes The Wheels Go Round?

No matter what kind of train you buy, electricity will run it. You may have chosen a choochooing, smoke-puffing steam engine or a growling diesel. It makes no difference, for a tiny electric motor working through a worm-drive makes the wheels go round. The motor pushes an extra piston on your steam loco, puffing out smoke which is really vaporized oil, and making the lifelike sounds of the engine. Electricity lights the headlight, blows the whistle, actuates the switch that sends your train into reverse. It throws your remote-control switches, works the uncoupler, causes the racing baggage car to pick up the mailbag on a stanchion without slowing down. Electricity operates your unloading cars, your talking station, and trackside load- ing devices. Since it does so many things, perhaps we should learn a little more about this versatile and powerful tool.

To perform work, electric current must flow. It cannot just travel up to a lamp bulb or motor and stop there. It must pass through the device, causing it to function as intended, and return to where it started. With direct cur- rent, the electricity is positive on its way to the device to be operated, negative on its return. The positive terminal is comparable to the north pole of a magnet, the negative to the south pole. The flow of electric current may be likened to the flow of blood in your body, which moves from the heart through arteries carrying oxygen and other essentials, reaches its destination and passes through it to deliver the needed materials, then returns to the heart by way of the veins. In the process it has performed some very useful work.

The current may be pushed along the wires with a good deal of pressure or force, which is measured in volts. A certain amount of electricity flows through the wire, and this rate of flow is measured in amperes. Finally, the cur- rent will do a certain amount of work, which is measured in watts. The amount of work depends upon the pressure behind the current, or voltage, and its rate of flow, or amperage. In the case of direct current, multiply volts times amperes and you get watts.  (With  alternating cur rent, another factor is involved, bearing on efficiency, but we need not go into that.)

How does electricity perform the work it does? In various ways, one of the most common being through resistance set up to it. To use a familiar example, if water is flowing over a dam and has nothing to impede its fall, there is no resistance. If you put a water wheel or turbine in the stream of water, the wheel offers some resistance to the flow. But the water pushes the paddles on the wheel out of the way and keeps flowing, thereby turning the water wheel and accomplishing work.

This is essentially what happens when a lamp bulb is lit, as shown in Fig 6. Electric current flows along copper wires, which offer very little resistance. Inside the light bulb it flows into fine filaments offering great resistance. The current flows in spite of this resistance but does some work in the process, by heating and making bright the filament.

What if the wire from the positive terminal should touch the wire from the negative terminal before it reached the bulb or other device to be operated? The current would flow from one wire to the other as if the dam had been broken. The rate of flow, or amperage, would suddenly increase so much that if the current was coming from a battery it would drain it completely in a very short while. If the current was coming from an electric inlet in your home, it would flow so rapidly that it would heat up another resisting device, known as a fuse, in your fuse box.

The fuse would burn up, or melt, so the current could not flow through it. This is a short circuit, and occurs whenever current is allowed to flow from one wire to the other without any resistance between them. If you didn't have a fuse to break off the flow of current at such times, so much heat might be generated that a fire would start.

Another method of breaking off the current in the event of a short circuit is the circuit-breaker, which is included in most train transformers. If your transformer does not have one, you can buy a circuit-breaker and connect it— a recommended safety measure. Most circuit-breakers establish the flow of current again automatically in a short while, but if there is still a short circuit it will immediately open and stop the flow. With electric trains, temporary snorts are often caused by a derailed train that lies across the tracks, or by a metal tool dropped across the tracks. If these are removed, the circuit-breaker establishes the flow of current again automatically, and you can proceed with the running of your trains. If the short circuit is not cor- rected, the circuit-breaker just keeps closing and opening continuously. Nothing on your train set will work under these circumstances, so you pull out the plug until you find the cause of the short circuit and correct it.

The circuit-breaker may also stop the flow of current if you have overloaded your transformer, tried to make it perform work beyond its capacity. Later we shall take up in more detail how to find short circuits and use your transformer properly.

Let's get back to the way in which electric current performs work on your model railroad. Its most important job, of course, is running the train. The train will run, naturally, whether you understand how a motor works or not. Most people, however, like to be familiar with the principles that lie behind work they do regularly. A few people, for instance, are perfectly happy to drive automobiles without having the faintest idea of what makes the engine turn over. Most drivers, on the contrary, like to understand the fundamentals even if they don't want to know enough to become mechanics. Model railroaders are much the same; most of them like to know what makes the wheels go round.

Electric train motors are based on the powers of magnetism. You know that every magnet will attract and hold pieces of metal. You know, too, that every magnet has a north pole and a south pole. If you have two magnets, the north pole of one will pull the south pole of the other toward it. It will repel or push away the north pole of the other magnet. This simple principle is what makes the electric motor go round.

In every electric motor there are two magnets, one fixed and the other mounted so that it can revolve on an axle, the shaft of the motor. One magnet may be a permanently magnetized piece of metal, the other an electromagnet, which is a piece of iron or steel with wire coiled around it. This acts as a magnet only when current flows through the wire. Or both fixed and moving magnets in a motor may be electromagnets.

In the simplified diagram (Fig. 7), the fixed magnet is shown as an electromagnet with north and south poles, marked N and S. Between them lies the armature, with three electromagnetic coils mounted on a rotating shaft, labeled A, B, and C. (On most real motors there are many more.) If current flows through A so as to make it a north pole, it will be attracted to the south pole of the fixed magnet and will move toward it, causing the armature to revolve. If, just as it passes the fixed south pole, current in A is stopped, then started in reverse direction to make it a south pole, it will be repelled and pushed away by S, and attracted by N, making it continue its rotation. Then, at the proper moment, the current is again interrupted and reversed so the fixed north pole repels A and the fixed south pole attracts it, causing it to continue its rotation. Since each armature coil goes through the same process, the motor shaft revolves smoothly. Each armature coil is continuously changing its polarity to get itself pushed and pulled around.

But how can you keep changing the polarity? By the commutator, which is mounted on the armature shaft but insulated from it, and consists of sections of metal insulated from each other, marked a, b, and c. When the armature has three coils, as here, the commutator has three sections, each of which is wired to a coil. Current flows from two wires to carbon brushes, marked Y and Z, which touch the commutator. As the armature turns, current flows through Y to section a of the commutator and thence to coil A. This flow of current is interrupted by the insulated section of the commutator, and then reversed as section a comes in contact with brush Z. The same series of changes occurs in each coil in turn as the motor goes round. The shaft of the motor, attached through the necessary gears to the wheels of your locomotive (Fig. 8), makes them turn. Your engine moves around the track.

As you know, there are two types of electric current, direct and alternating. Direct current flows always in one direction, and is the type that comes from batteries and that is supplied in a few homes. Most common household current is alternating, in which the polarity of the wiresis rapidly changing at all times, as the current changes direction. In most homes, the change is made every 1/120of a second, so that a complete cycle comes every 1/60 of a second. This is 60-cycle alternating current.

With alternating current, a permanent magnet cannot be used in an electric motor. The fixed magnet which encircles the armature, called the field, must be an electromagnet, wound with wire like the armature, because the continuous changes of direction of alternating current must take place in both armature and field if the motor is to run.

There are numerous advantages to alternating current, one of which is that its voltage can easily be reduced by means of a transformer. The 110-volt current of most houses would not be safe for use with model trains, of course, where current flows through exposed tracks. So the voltage, or force behind the flow of current, must be reduced considerably.

Alternating current possesses the faculty of induction. It can set up a flow of current in another wire that is not connected with it. If you wind a coil of wire around one arm of an iron core and another coil of wire around the other arm, as in Fig. 9, an electric current will be set up in the second wire when current passes through the first wire. If the number of turns of wire is the same on both sides, the voltage will be approximately the same in both wires. If the number of turns in the second coil is less, the voltage will be less. You can control the voltage of the sec- ond coil of wire by the number of turns you make in relation to the number of turns in the primary wire. Not only that, but you can make a little device that will pick up the current on the secondary coil at any point you want after twenty turns, or forty, or sixty. Thus you can select different voltages from your secondary coil.

That is how you make your train go faster or slower. Your transformer contains a coil reducing the voltage of your household current to sate proportions, usually ranging from 7 to 15 or 18 volts. The control lever picks up varying voltages from the secondary coil as you move it-seven volts at the lowest point, fifteen to eighteen volts at the point of highest speed. As higher voltage flows from transformer to the motor in your locomotive, it goes faster, moving your train at increasing speeds. As you push your control lever back, lower voltages of current go to the motor and your train slows down.

 

How can you make your train back up? By causing the electric motor itself to turn in the opposite direction. With DC current, as used with most HO trains, this is done simply by a switch on your control panel which sends the current through the wires in the opposite direction. South poles thus become north poles in your motor and are repelled or attracted in reverse order. With alternating current, a special type of switch actuates what is called sequence reverse, usually carried in the tender of your locomotive. This switch (Fig. 10) is worked by the making or breaking of the current being fed to the train motor.

Let's assume the train is moving forward and is then stopped. Breaking the flow of current serves to move the sequence switch to a neutral position, so that when you turn on the current again, it cannot flow to the motor because this switch is open. It can, however, flow to lamp bulbs in your train; only the motor is cut off. Now, shut off the current again, and the sequence switch will move to still another position, in which the wires leading to the armature are reversed in their relation to the field leads.

When you cause the current to flow again, the motor will turn in the reverse direction and your train will back up. Another off-on switch of current and you are in neutral again; another and your train will move forward. In other words, the switch passes through a sequence of positions-forward, neutral, reverse, neutral, forward, and so on.

Model railroaders have grown adept at handling the sequence reverse, lifting the control lever on the transformer the proper number of times to make and break current and send the train in the direction they want. In recent years, however, many transformers have been made to give complete directional control without the necessity of manipulating the control lever in this way. As you push the lever back to its lowest voltage point, current is not completely cut off; enough still flows through to keep the sequence switch from operation, even if not enough to make the train motor turn over. The train stops, but lights remain lighted and the sequence switch does not move. When you move the control lever to feed more current to the motor, the train moves forward in the same direction. In order to actuate the sequence switch, you must lift the control lever so as to break all flow of current completely. Directions that come with your transformer will tell you how to handle the control lever so as to give you complete directional control over your train.

 

Transformers vary in size and capacity, in the types of control levers, in the presence or absence of voltmeters, ammeters, on-off switches, warning lights for short circuits, circuit-breakers, etc. But on all of them (Fig. 11) you will find at least three terminal posts on the back for hooking up 'wires—three threaded metal posts with nuts on them. One of these posts supplies current that varies involtage from seven to fifteen or, in the newer transformers, from seven to eighteen; this is for operation of your train. A second post supplies a fixed fifteen or eighteen volts, primarily for the operation of accessories. A third post is the base post, to which the returning wires from both train and accessories are attached to complete the electrical circuit. As Fig. 11 shows, dual transformers, for the control of two trains at the same time, have two sets of binding posts.

It is simple to attach wires to these posts by cutting away the insulation about half an inch from the end, winding the bared wire around the posts, and tightening the nuts down on the wire. But how does the current get from this point to the motor in your locomotive?

It travels down the wire attached to your variable-volttage post (marked 7-15 or 7-18) to a track terminal that clips to the track (Fig. 12). This snaps on to make a good, tight connection. The bared end of wire from the variable-voltage post slips under a spring clip on the track terminal.

Another wire (use a different color so you can tell them apart easily) goes from the base post to the other spring clip on the track terminal. Directions that come with your train will tell you which clip is which. From this point the electric current flows through the tracks themselves, one rail carrying current to the motor in the locomotive, another rail carrying it back to the base post.

 

If you look at your track carefully, you will see that the rails are insulated from the metal ties by pieces of fiber, which cannot conduct electricity (Fig. 13). If this fiber were not there, current would pass through the ties from one rail to another, cause a short circuit, and never reach your motor. But the tracks are insulated, just as the wheels of your locomotive tender are insulated from the metal parts of the tender and locomotive as well as from each other. (On HO tracks, the ties themselves are nonconductors, so no insulation is needed.)

Most of the wheels on your train are made of plastic, non-conducting material, and will not pick up any electric current from the tracks. On the tender of your steam loco, however, or one truck of your diesel, you will find metal wheels and sometimes a metal shoe which make contact with the rails, allowing the current to flow from one rail to the wheels on that side. From the wheels, a wire runs to the switch and from it to the motor which runs your train. The wire leading away from the motor and switch carries the current to the metal wheels on the other rail, along which it travels back to the track terminal, up the wire to the base post of the transformer, as shown in Fig. 14.

Current running through the track also actuates a few of the accessories you may eventually want to have, such as semaphores, crossing gates, and signals of different kinds. But most accessories use current directly from the fixed voltage (15 or 18) post on the transformer, as seen in Fig. 15, which shows a cattle-loading stockyard. You can easily wire such accessories if you follow the directions and clear diagrams that accompany each piece of equipment you buy. With a good number of accessories and a layout more interesting than a simple oval, you will want to hide the many wires and simplify the wiring somewhat. Details on the best way to do this will be found in a later chapter.

 

Meanwhile, you will attach your first accessories on the floor or table where you have your trains and will enjoy them immensely. A great deal of ingenuity has gone into the making of these accessories that will throw switches, load or unload a variety of things, blow whistles, operate signals, stop your train automatically at a station, announce its destination, and start it up again. In some accessories an electromagnet is used; current passes through a coil of wire, turning it into a magnet which attracts a piece of metal and makes some mechanism work. In others, there is a solenoid, which is a kind of hollow, tubular elec- tromagnet with a metal plunger inside, as shown in the simplified diagram in Fig. 16. When no current flows through the solenoid, gravity or a small spring holds the plunger outside, but when current flows and creates a magnetic attraction, the plunger is pulled inside, making another device move somewhere. Electric vibrators make cattle mill around in a pen. A small motor may run a crane with an electromagnet. A tiny motor runs an actual phonograph hidden in the talking station so that a record calls out the stations on the line and says, "All aboard!"

There are so many different devices that they can be made to do just about everything you want in connection with your railroad. And they are all run by electricity.

But none of these accessories, or the train itself, will operate properly if you don't have good electrical connections. At the outset, of course, you don't need to worry about this at all. The manufacturers, with their simple terminal posts and clips, have made the elementary wiring just about foolproof.

Speaking of accessories, you must remember that they use current, and this brings up the size or capacity of the transformer you buy. In some cases, transformers come as part of the train sets, and these are usually capable of putting out fifty or one hundred watts of work, enough to run a train and a few accessories. If, later, you extend your layout a great deal, adding more trains and many accessories, you will have to get another transformer to handle the load. Then you can use one transformer for running your trains, the other for accessories, if you wish.

If a transformer does not come with your train set and you buy it separately, you will have to decide the size of transformer needed. Naturally, the larger it is the more expensive it will be, but it is a good idea to plan ahead if you can. If you know that within a relatively short time you will be adding more track, more trains, a good number of accessories, it is best to buy a transformer that will take care of your needs for some time to come. They range in size from fifty to three hundred watts. Some have two controls for operation of two trains at different speeds at the same time, or four trains at once, two each at the same speed.

In calculating your needs, remember that there are two types of drain on the electric output of your transformer continuous and intermittent. In other words, when you are operating your train, some devices draw current all the time, others only occasionally. For example, lamps usually burn steadily after you plug in your transformer.

Since your train will presumably run most of the time, it is safest to figure it, too, as in continuous operation.

On the other hand, most accessories operate and draw current only at certain times and for short periods switches, whistles, uncouplers, semaphores, talking stations, loading and unloading devices. Some of these oper- ate while your train is moving, such as switches, uncouplers, crossing gates, semaphores, highway flashers. Others are more likely to function when the train is stopped and not drawing current, such as loaders and unloaders and the talking station. You may, however, operate a cattle loader and its car on a siding while the train continues to speed around the main line. This is especially true when more than one operator is working your pike.

The best procedure is to total the amount of current likely to be used at any one time, adding together the watt- age of your train, lamps, and various other accessories that could conceivably draw current at the same moment. You can learn the watts demanded by various devices from the store or manufacturer, but approximate figures can be given here. Small steam locomotives like switchers generally draw about twenty watts, larger steam locos about thirty watts, diesel switchers about twenty watts, large diesels from forty to sixty watts, operating accessories from ten to forty watts, and each lamp about three watts. After getting your total of watts likely to be used at one time—now and in the near future—buy a transformer that will amply cover those needs, and with plenty to spare.

Never figure on using more than three quarters of the rated wattage of the transformer. Transformers are rated at their top capacity for short periods and will heat up, perhaps burn out, if they are used at that capacity for any length of time. If you need 125 to 130 watts, for instance, be sure to get at least a 175-watt transformer. There's nothing wrong with having a transformer whose capacity is greater than demands upon it, but there is a danger of ruining a transformer that is overloaded or even used steadily anywhere near the peak of its rated capacity.

Your transformer will have a speed indicator on it, a dial over which the control lever passes, but this may not always be accurate because the drainage of accessories may reduce the voltage going to the train. You will probably enjoy checking the speed of your train, in any event, as many model railroaders run their trains far too fast. In Sgauge, remember that you are working with trains that are 1/64of the size of the originals. Thus a mile, for your train, will have to be 1/64 of a real mile, or about 82 1/2 feet. If your train travels 82 1/2 feet in one minute, it is moving at a scale speed of a mile a minute, or sixty miles an hour. Some hobbyists have watches or clocks running at scale time, or scale miles laid out on their track. But you need not go that far to check the speed of your train.

Figure your train's speed in track lengths rather than feet. In S gauge, each track section is ten inches long, so there will be about 99 sections in a scale mile. If you have an oval of track with twenty sections, the train should go around it five times in a minute to be making a speed of sixty miles per hour. If your layout contains 25 sections of track, four times around in one minute is sixty miles per hour.

Another way to figure speed is to know that your train travels 1.6 track sections per minute for each mile of speed per hour. Thus, if it covers 16 track sections in one minute, it is going ten miles an hour. Thirty-two track sections per minute means that it travels 20 miles an hour, forty-eight sections means thirty miles an hour, sixty-four sections a minute is forty miles an hour, eighty track sections equals fifty miles an hour, and so on.

Hook up your train, set it moving, and check its speed against your watch. Make it slow down for curves, as real trains do, pick up on the straightaways. When you get switches, remember that trains enter switches at reduced speed, slow down for some bad crossings, and pick up speed slowly after leaving a station. You will begin to enjoy model railroading even more when you know the speeds at which you are running your train.

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