The following are the data for two crossed helical gears

The following are the data for two crossed helical gears used for speed reduction:
Gear I: Pitch circle diameter in the plane of rotation 80 mm and helix angle 30°
Gear II: Pitch circle diameter in the plane of rotation 120 mm and helix angle 22.5°
If the input speed is 1440 rpm, the output speed in rpm is

For helical gears

Velocity ratio =	d₁ cosφ
	d₁ cosφ

=	80 cos30°	=	N₂
	120 cos22.5°		N₁

∴ N₂ = 1440 × 0.625 = 900 rpm