Gears, Gears and More Gears
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 seminar class Active In SP Posts: 5,361 Joined: Feb 2011 16-02-2011, 12:41 PM   gears.ppt (Size: 421 KB / Downloads: 203) Gears, Gears and More Gears What is a gear? A gear is a wheel with teeth that mesh together with other gears. Gears change the • speed • torque (rot. force) • direction of rotating axles. Different types of gears Spur gears Idler gears Worm gears Bevel gears Belts & Pulleys Spur Gears Most “common” type of gear, a wheel with teeth Spur gears do three things. 1. Change rot. speed 2. Change torque 3. Change direction Make sure there isn’t too much friction between the gears and the beam. The gears should spin easily Gear Ratios The gear ratio is the ratio of the number of teeth on one gear to the number of teeth on the other gear Gear ratio = 40 to 8 or, simplifying, 5 to 1. That means it takes 5 revolutions of the smaller gear to get 1 revolution of the larger gear The gear ratio tells you the change in speed and torqueof the rotating axles.If it takes 5 turns of the 8 tooth gear for every 1 turn of the 40 tooth gear, that means the 40 tooth gear will rotate 5 times slower than the 8 tooth gear.BUT, it also means the 40 tooth gear’s axle has 5 times the torque (rotational force) as the 8 tooth gear’s axle Idler Gears An idler gear is a gear that is inserted between 2 other gears Build the following. Add another 8 tooth gear to the right of the40 tooth gear. How many turns of the 8 toothgear on the left does it take to make 1 turn of the new 8 toothgear on the right? Answer: 1! It’s as if the 8 tooth gears are meshed together. Idler gears DO NOT change the gear ratio. Idler gears DO… • make both 8 tooth gears rotate in the same direction, add spacing between gears Bevel Gears Bevel gears are spur gears that mesh at a 90 degree angle. The gear ratio rules remain the same, but the axles are perpendicular to one another Worm Gears Worm gears have some special properties 1: The axles are perpen-dicular, like bevel gears. 2: How many rotations of theworm gear does it take for 1rotation of the spur gear? The worm gear acts like a gear with 1 tooth! This givesvery large gear ratios. Worm gears are not back - driveable You can turn the worm gear’s axle, but you can’t turn the spur gear’s axle.This property is used as a locking mechanism Belts & Pulleys Belts & pulleys are related to gears. They change speed and torque, but with a few differences... Pulleys transfer their force by the friction of the belts, rather than direct contact with the teeth of gears. This can cause the belts to slip.Unlike gears, the pulleysrotate in the same direction. Belts can transfer force across long distances Like gears, however, belts and pulleys do have a “gearratio.” It is the ratio of the diameters of the pulleys