# Why is double Hookes joint used? - Theory of Machines - 1

Q.  Why is double Hooke's joint used?
- Published on 06 Aug 15

a. To obtain uniform velocity ratio
b. To obtain variable velocity ratio
c. Both a. and b.
d. None of the above

ANSWER: To obtain uniform velocity ratio

#### Discussion

• Sravanthi   -Posted on 21 Oct 15
- If a single Hooke's joint is used, velocity of driven shaft is not uniform even if driving shaft rotates at uniform velocity. This variation of speed is depicted on a polar diagram.

- A double Hooke's joint is used to obtain uniform velocity ratio. A double Hooke's joint gives uniform velocity ratio if:

1) Axis of driven and driving shaft are in same plane.
2) Input and output shafts make equal angles with the intermediate shaft.

- The driving and driven shafts in double Hooke's joint rotate at same angular speed, hence velocity ratio is unity.

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