What are gears? Wheels with teeth

Why gears? They transfer motion from 1 part to another. Gears can increase speed. Gears can be used to pull heavy loads. But… …not both.

Torque Torque can be described as a force causing rotational acceleration, that is, causing something to spin. Torque=Applied Force * distance to pivot Greater force or longer distance means more torque

Motors Motors deliver torque in a small package They can be used wherever rotational motion is needed. Motors differ in the amount of torque they output and the speed at which they spin.

Gearing - Why? You don’t always have the perfect motor for the job Gearing is used to change the speed and torque output of a motor to suit your design needs Gearing results in a compromise between speed and torque. To gain speed, you must sacrifice torque. To gain torque, you must sacrifice speed.

Gear Ratio Gear ratio is defined as: Expressing the ratio: Drive gear (input): driven gear (output) Number of Teeth Input : Number of Teeth Output Expressing the ratio: 5:2 = 5/2 = 2.5:1

Examples Therefore, drive gear must turn 3 times Meshing 8-tooth gear with 24-tooth gear yields 1:3 gear ratio. 1 turn moves 8 teeth here… …and here Therefore, drive gear must turn 3 times

Ratios Drive gear Driven gear 2 2 2 1 1:1 2:1 Odd number gear meshes change direction

What is this ratio? 1:5 5 t Motor attaches here 25 t Input: Output 5:25 1:5

Gear train: a collection of gears The ratios have a multiplicative effect. 8 t Motor 24 t 8:24 = 1:3 3 x 2 = 6 1:6 24:48 = 1:2 48 t 8:48 = 1:6

Multiplicative Effect 8 4 1 1:2 Drive 1:4 Overall ratio 1:8

Gearings effects on Torque Force acting through a distance. Radius of gear is the lever arm. Small radius = small lever arm Large radius = large lever arm

Gearing vs. torque r 2r .2kg•m .4kg•m

Worm Allow for VERY large reductions Unique feature: gear Allow for VERY large reductions i.e. 20:1 to 300:1 Unique feature: The worm can turn the gear but.. The gear cannot turn the worm