# Why is an idler gear used in gear trains? - Basic Mechanical Engineering

Q.  Why is an idler gear used in gear trains?
- Published on 01 Sep 15

a. To obtain minimum centre distance between driving and driven shaft
b. To have required direction of rotation
c. Both a. and b.
d. None of the above

ANSWER: To have required direction of rotation

#### Discussion

• Nancy koech    -Posted on 09 Mar 21
I love this
• Aadi   -Posted on 10 Dec 16
• Sravanthi   -Posted on 06 Nov 15
Gear train: Combination of gears transmitting power and motion from one shaft to another shaft is known as gear train.

- These gear trains are used to reduce or increase speeds from input shaft to output shaft or to maintain same speed from driving shaft to driven shaft.

- An idler is placed between driving and driven gear in a simple gear train. These idler gears are used to obtain large centre distance between driving and driven shafts and also to obtain desired direction of rotation of the driven shaft.

- This idler gear is inserted between driving and driven gear and used for supporting purpose.

- The direction of rotation of driven gear is opposite to direction of rotation of driving gear, if even number of idler gears are used such as 2, 4, etc.

- The direction of rotation of driven gear is same as driving gear, if odd number of idler gears are used such as 1, 3, 5, etc.

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