Gear Train Types

There are various types of gear trains used in mechanical systems. One of these types is an epicyclic gear train, which is characterized by having at least one of the gear axes in motion relative to the frame. Let's understand the different types of gear trains and why the correct answer is option 'D'.

1. Simple Gear Train:
A simple gear train consists of two or more gears that are meshed together. The axes of all the gears are fixed relative to the frame, and the gears rotate about their fixed axes. This type of gear train is widely used in various machines and mechanisms.

2. Compound Gear Train:
In a compound gear train, there are two or more gears on each shaft. The gears on each shaft are fixed relative to each other but can rotate about their own axes. However, all the gear axes are fixed relative to the frame. This type of gear train is often used when there is a need to change the direction of rotation or to achieve a specific speed ratio.

3. Reverted Gear Train:
A reverted gear train is a combination of a simple gear train and a compound gear train. It consists of two or more gear pairs, with each gear pair having two gears meshed together. The axes of one gear pair are fixed relative to the frame, while the axes of the other gear pair can rotate about their own axes. This type of gear train is used to achieve a specific speed ratio while changing the direction of rotation.

4. Bevel Gear Train:
A bevel gear train uses bevel gears, which have conical-shaped teeth. This type of gear train is used when the direction of rotation needs to be changed by 90 degrees. The gear axes are fixed relative to the frame, and the gears rotate about their fixed axes.

5. Epicyclic Gear Train:
An epicyclic gear train, also known as a planetary gear train, is characterized by having at least one of the gear axes in motion relative to the frame. This means that the gear axes can rotate about their own axes while also rotating about a common axis. It consists of a central gear, called the sun gear, surrounded by one or more planet gears and an outer ring gear, called the annular gear or ring gear. This type of gear train is commonly used in automatic transmissions, gearboxes, and differentials.

Conclusion
Based on the explanations of different types of gear trains, it is clear that an epicyclic gear train is the correct answer to the given question. In an epicyclic gear train, at least one of the gear axes is in motion relative to the frame, which differentiates it from other types of gear trains.

In option a, b and c the axes of gears are stationary. They do not move. But in epicyclic gear trains using an arm, the axes of one or more gears can move relative to the frame.