Gear velocity ratio for Simple and Compound Gear train. Reduction or Multiplier gear?

In this webcast, we define the gear or velocity ratio for a simple gear train and a compound gear train. Whether a gear train is a reduction gear or a multiplier gear based on power direction is explained. #geartrain #compound_gear_train #simple_gear_train #gear_ratio

[@muyiwajayeola1389]

Pls this!
A driving gear having 25teeth engages with a second gear with 20teeth. A third gear with 30 teeth on the same shaft as the second one engages with a fourth gear having 60teeth. Find:
a) The total velocity ratio of the system.
b) The mechanical advantage of the system if its efficiency is 85%.

[@MohammadShafinulHaque]

For the first part (a) follow the instructions described 3:00 min onwards.

[@johnmifsud6814]

why are the velocity ratios multiplied ?

[@MohammadShafinulHaque]

One way to look at it as the multiplication of the velocity ratios cancels the idler gear from calculation. In this case, B is the idler gear, and ratio multiplication cancels idler gear number of teeth from consideration. And the overall ratio depends on driver and follower gear. No matter how many idler gear you may have doesn't affect the overall ratio, and multiplication makes it right.