Understanding Gear Trains and Co-axial Axes

A gear train is an assembly of two or more gears used to transmit power and motion from one shaft to another. The arrangement of gears determines the type of gear train and its characteristics, such as speed ratio and the relative position of input and output shafts.

The question asks about a specific type of gear train where the axis of the first gear (input shaft) is aligned with, or co-axial with, the axis of the last gear (output shaft).

Defining the Reverted Gear Train

A gear train where the axis of the final output gear coincides with the axis of the initial input gear is called a reverted gear train.

This type of gear train is commonly used in applications like clockwork, industrial speed reducers, and lathe gearboxes where the input and output shafts need to be aligned for compactness or specific design requirements.

Reverted gear trains are typically constructed using a series of gears mounted on different shafts, arranged such that the axis effectively "reverts" back to the original line.

Comparing with Other Gear Train Types

• Simple Gear Train: In a simple gear train, each shaft carries only one gear. While gears can be arranged in a series, the axis of the final gear is typically offset from the axis of the first gear.
• Compound Gear Train: A compound gear train has at least one shaft carrying two or more gears. This allows for larger speed reductions or increases in a smaller space. A reverted gear train is a specific type of compound gear train designed to achieve co-axial input and output shafts. Not all compound gear trains are reverted.
• Epicyclic Gear Train: Also known as a planetary gear train, this type involves gears orbiting around a central sun gear. While providing high speed ratios and compactness, the fundamental characteristic is the relative motion of axes, not necessarily the co-axial alignment of the initial input and final output shafts in the manner of a reverted train, although certain epicyclic arrangements can result in co-axial shafts.

Conclusion

Based on the definitions, a gear train where the axes of the first and last wheels are co-axial is specifically identified as a reverted gear train.