The main difference point between a simple gear train and a compound gear train is that in the simple gear train, each shaft is equipped with only one gear, whereas in the compound gear train, at least one intermediate shaft is equipped with two or more gears of varying sizes.
Simple gear train:
The simple gear train consists of input gear (driver gear), output gear, and intermediate idlers.
In this gear train, the input and output gears are responsible for the gear ratio while the idlers have no effect on the gear ratio.
The purpose of idlers in a simple gear train is to alter the direction of rotation of the output gear or to adjust the center distance between shafts of input and output gear.
The simple gear train is not suitable to achieve a higher gear ratio as its size increases with an increase in gear ratio. Therefore the simple gear train has limited applications.
Compound gear train:
The name of the compound gear train says itself that it contains at least one intermediate shaft with compound gear.
The compound gear consists of attaching two or more gears of different sizes together and mounting them on the same shaft.
As shown in the below figure the compound gear train consists of input gear, output gear, compound gear, and/or idler.
The compound gear train can easily obtain a higher gear ratio within limited space. Thus the compound gear train is used in plenty of applications.
Difference between simple gear train and compound gear train:
| Sr. No. | Simple gear train | Compound gear train |
|---|---|---|
| 1 | In a simple gear train, a single gear is mounted on each shaft. | The compound gear train has two or more gears mounted on the same shaft. |
| 2 | The gear ratio only depends on input gear and output gear. | The gear ratio depends on input gear, output gear, and intermediate compound gears. |
| 3 | It is difficult to obtain a higher gear ratio in a simple gear train. | It is easy for the compound gear train to obtain a higher gear ratio. |
| 4 | It requires more space. | It is more compact as compared to a simple gear train. |
| 5 | All intermediate gears in the simple gear train are idlers. | The intermediate gear in the compound gear train are idlers and compound gears. |
| 6 | The simple gear train has limited applications | It has huge applications. |
