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1)
Explain how a modern diesel or electric locomotive develops power.
2) Explain the terms Dynamic Braking and Radial Steering Trucks.
If you think about a regular car (not a Hybrid car), or a truck, the petroleum-fueled motor drives the axles mechanically, through a mechanical transmission system.
A Modern Diesel-Electric locomotive has a diesel-fueled motor, but it does NOT drive the wheels mechanically! Each axle of the locomotive is an independant electric motor!
Here is the reason it sounds like the diesel motor is turning the wheels...
When you make a generator work (asking it to exert more electrical power to run lights and motors), the generator becomes harder to turn. When the engineer asks the motors to make a train move faster, the generator in the locomotive becomes harder to turn, so you will hear the diesel engine also working harder (to turn the generator).
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The Engineers Controls are used to supply power, of the correct polarity, to the electric Traction Motors, which causes the locomotive to move forward and backward. Those controls include;
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The modern locomotives have three types of brakes that the engineer can employ.
The Independant Brake only controls the brakes on the locomotive(s), without setting all of the brakes on the rest of the train. The Train Brake uses air pressure on the Train Line to control the brakes on every car on the train.
Both the Independant and the Train Brakes use mechanical braking. Dynamic Braking slows the train by turning the electric train motors into generators! The engineer makes the electric motors work, by sending the power from the motors to a resistor grid (which turns the power into heat), and to fans (which blows the heat out the top of the locomotive). By doing this, the motors are harder to turn, which is effectively slowing the train down, without using the mechanical brakes!
If you are interested, you can view a locomotive air brake block diagram.
| Dynamic Braking can be used when the train is coasting. Because the
Traction Motors are not using electricity to move the train, the engineer
can make the wheel motors generate electricity instead, by connecting
the motors to a Resistor Grid and Fans near the roof of the locomotive. The
power from the motors is turned into heat, and the fans help blow the heat out
the vents on the roof of the locomotive.
When you ask a generator to produce power, the generator becomes harder to turn. When the train is coasting, the motion of the wheels generates power. When you use the power from the wheels to make heat, the wheels become harder to turn, which helps to slow the train down, without using the brake shoes. |
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Radial Steering Trucks are a special adaptation of the Traction Motor Wheelset under a locomotive, which was meant to solve a specific problem that caused wear and tear on the wheels and the rails. In order to understand why the solution was made, you should understand the problem.
Most train car trucks (wheelsets) have two axles, mounted parallel to each other. The wheels have a very close alignment to the rails. Because the top of the rail and the edge of the wheels are not very wide, the clearances need to be close.
When trucks go around a curve, the gap becomes even smaller, and that can cause
extra wear and tear at the pinch points, shown in the image to the right. (The curve
is exaggerated, to highlight the problem areas.) |
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When bigger, heavier, six-axle locomotives came along, the problem was even worse. This wear and tear made the railroads have to do more maintenance work on the curves, as well as the locomotive wheels wearing out sooner. Both of these were very expensive, and this was the problem that the railroads wanted to solve. The solution was Radial Steering Trucks.
These special locomotive trucks could sense when the locomotive
was going around a curve, and it could let the leading and trailing axle change
their angle a bit, to try to match the curve. This would reduce the pinch point
trouble under these heavy locomotives, an would help extend the working lifetime
of the curves and the traction motor wheels. |
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There are currently 120 active merit badges that can be earned by Boy Scouts today, and scouts can find information about all of these on the Internet at the Merit Badge Research Center (MBRC) website, including the Railroading merit badge requirements. The MBRC has worksheets for most of the current merit badges.