GEAR RATIOS

Putting Gears to Work Reverse direction of rotation Increase or decrease the speed of rotation Move rotational motion to a different axis Keep rotation of two axes synchronized

Understanding Gear Ratio Circumference of a circle – Diameter multiplied by Pi –1.27” x 3.14 = 4.0” Circle with diameter has a 2” circumference Smaller gear rotates twice for each rotation of larger gear, gear ration is 2:1

Gear Teeth Prevent slippage between gears – synchronizes Counting teeth on each gear determines exact gear ratio –If one has 60 teeth & the other has 20, the ratio is 3:1 Slight imperfection in gear diameter doesn't matter, ratio is controlled by number of teeth

Gear Trains To create large gear ratios, several gears are connected together

Worm Gear Creates very high gear ratio Threaded shaft engages teeth on a gear For each turn of shaft the gear moves one tooth, if gear has 40 teeth, 40:1 gear ratio is achieved

Planetary Gear Train Say you want gear ration of 6:1 with input & output gears moving in same direction Planetary gears are very compact & produce the same effect

Planetary Gear Train Different gear ratios can be achieved depending on which gear is the input & output & which one is held still Automatic trans use this gear set to achieve different ratios for each gear range. Using clutches & brake bands to hold different parts of the gearset stationary & change inputs & outputs

Gear Synchronizing To have two gears that are far apart rotation in the same direction, put a big gear between them Or use two small gears between them A more practical approach is to use a toothed belt or chain