Mechanical Engineering: Gears

Wheel and axle F1 x D1 = F2 x D2 Lower force x longer distance = higher force x shorter distance

Wheel as force multiplier Wheel as speed multiplier Can you think of other examples?

Gears – wheels with teeth Gears have teeth that can be meshed together to effectively transfer motion from one gear to another. Gears are used for: Changing the direction of rotation Changing the speed of rotation Changing the force required to move an object Moving the rotational motion to a different axis

Drawing Gears It can be difficult to draw all those teeth so gears are often drawn as two circles and the number of teeth noted.

Changing direction What direction do the driven gears move, given that the driving gears move clockwise?

Changing speed Would the driven gear move faster, slower or the same speed as the driver? Driver Driver

Gear Ratio To find quantitatively how the motion will change in gear system you can use gear ratios With gears, you can compare the radii of the gears (as in wheels) or you can compare the number of teeth. The driven gear makes two rotations each time the driver rotates. So it moves twice as fast. Speed out = Speed in / gear ratio

Gear Ratios What are the gear ratios for these systems? Driven gear moves 1/3 the speed of driver Driven gear moves 1/4 the speed of driver

Gear speed If the driver is moving at 60 rpm (revolutions per minute) what speed is the driven gear moving? Speed out = Speed in / gear ratio

Compound Gear Ratios When faced with multiple gears systems: - find each gear ratio - multiply them together to find the overall ratio

Changing force Gears can be used to change the force needed. Force with rotation involved is called ‘torque’. The change in torque can be found with gear ratios Speed out = Speed in / Gear ratio Torque out = Torque in x Gear ratio There would be 3 times the force on B than on A

Changing axis of rotation Gears can be used to change the axis of rotation by using Bevel gear Worm gear

Complex Gear Machine Use two gear ratios to find the speed of the final gear in this system

Complex Gear Machine Use two gear ratios to find the speed of the final gear in this system