2 What are they? GEARS Benefits Wheels with mating teeth cut in the rim or surface so that one can turn the other without slippage.The lever is basic to gearing. A pair of gears is essentially a set of spinning levers each with two equal arms acting in turn.BenefitsChange the plane of rotation.Increase or decrease the speed of applied motion.Increase or decrease the applied force.Provide a drive without slippage.
3 Gears Driver Gears: are directly driven by a motor Drive GearDriven GearDriver Gears: are directly driven by a motorDriven Gears: mesh with the driver gear
4 Gear RatiosMechanical Advantage: The PRODUCT of the number of teeth on the DRIVEN wheel (gear) DIVIDED BY the number of teeth on the DRIVER gearA "ratio" is a comparison. In the case of gears, it is the comparison of TURNS OF INPUT to TURNS OF OUTPUT.Example: A gear ratio of 5:1 ( an 8 toothed gear turning a 40 toothed gear), the input shaft must make five revolutions to produce one revolution of the output shaft.Output speed is five times slower, but the output torque is five times greater!
5 Gear Ratios Lets take a look…..Figure out the following gear ratio’s Hint: Output/Input1.Drive3.Drive4.2.DriveDrive
6 Gear Ratios How did you do? 3. 1. 4. 2. Drive Drive Drive Drive 20 to /20=.9:113 to /13=2:14.DriveDrive2.9 to 20 20/9=2.22:125 to 13 13/25=.52:1
7 Speed vs. Torque How do we achieve one or the other? Shapes Drive Gear: Large gear with more teeth attached to a smaller gear with less teeth will =more speedDrive Gear: Small gear with less teeth attached to larger gear with more teeth will = more torqueShapesWhich are stronger?Drive GearDrive Gear
8 Speed vs. Torque Real World Example Ford F150 has a 4.10 gear ratioDrive shaft will turn about 4x & the rear wheel will turn 1xGreat for towing not on mpg’sWhy do you think a 5-speed manual Ford Mustang is geared as followed?Gear 1, 3.35:1 RatioGear 2, 1.93:1 RatioGear 3, 1.29:1 RatioGear 4, 1.00:1 RatioGear 5, 0.68:1 Ratio (Overdrive)
9 Types of Gears Spur Gear Most common gear, straight teeth, mounted parallelHelical GearSimilar to the spur gearTeeth are cut at an angle for smother transitionBevel GearUsed when the direction of a shaft's rotation needs to be changedUsually mounted at 90 degrees apart
10 Types of Gears Worm Gear Used for large gear reductions (20:1, 100:1) Worm can turn the gear, gear can not turn wormRack & Pinion GearUsed to convert rotation into linear motion.
11 Gear Review What is a gear? What is the MA of a drive gear with 10 teeth and a driven gear of 35 teeth? Would that set up produce more torque or speed?What is the difference between the drive gear and driven gear?What are some benefits of gears?
12 Gear Review1. Wheels with mating teeth which turn each other without slipping.2. 3.5:1- torque3. Drive is attached to motor; driven gear is turned by drive4. Increase speed, torque, change in output direction, provide a drive with no slipping
13 Gear Review How Gears Work Worksheet www.howstuffworks.com Complete the provided worksheet30 pts.Each student must submit his or her own worksheet