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What are Gears?. Gears are wheels or cylinders with teeth that mesh with the teeth of other gears to transmit motion Gears are used in everything from automobiles to small toys. Functions of Gears. Transfer Motion Change Direction Increase/Decrease Speed Increase/Decrease Torque

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what are gears
What are Gears?
  • Gears are wheels or cylinders with teeth that mesh with the teeth of other gears to transmit motion
  • Gears are used in everything from automobiles to small toys
functions of gears
Functions of Gears
  • Transfer Motion
  • Change Direction
  • Increase/Decrease Speed
  • Increase/Decrease Torque
    • Torque is turning or twisting force. Ex: A longer wrench gives you more torque and makes it easier to loosen a bolt or screw.
  • Change Planes of rotation
drivers followers
Drivers &Followers

A driver is the gear which is being turned by a power source (motor or your hand).

A follower is turned by the driver.

motor

motor

Follower

Driver

Follower

Idle

Driver

spur gears
Spur Gears
  • Transfer motion within a plane (a straight line)
  • Most common gear
  • Spur gears are made in many different sizes and from a number of different materials
    • Steel, plastic, etc.
  • Spur gears are generally identified by the number of teeth they have
spur gears5
Spur Gears
  • Gears are attached to axles which run through the center of the gear
  • Gears must be positioned just right, so that they do not push on each other but the teeth will still turn the other gear

Meshing gears turn in

opposite directions.

lego spur gears
Lego Spur Gears
  • Common sizes are 8, 16, 24, and 40 tooth
  • Correct Spacing
    • Horizontal
      • 40 and 24- 3 holes between axles
      • 40 and 8- 2 holes between axles
    • Vertical
      • 40 and 24- 2 studs and 1 plate between studs holding axles
      • 24 and 16- 1 stud between studs holding axles
  • Gears can be placed in a number of other combinations diagonally, but none other vertically or horizontally
gears mesh
Gears Mesh
  • The teeth on gears mesh together so that 1 tooth on 1 gear pushes past 1 tooth on a second gear.
  • 1 turn of the driver will turn the follower around 1 time.

Driver: 40 tooth gear

Follower: 40 tooth gear

gearing down
Smaller gear is the driver

Larger gear is the follower

The driver (smaller gear) has to turn around multiple times to get the follower (larger gear) to turn around once

Gearing down gives you a slower speed (because it takes multiple turns of the driver to turn the follower once)

Gearing down also gives you more torque

Gearing Down

Driver: 8 tooth

Follower: 40 tooth

The driver has to turn around 5 times to get the follower to turn once

gearing up
Gearing Up
  • Larger gear is the driver
  • Smaller gear is the follower
  • The driver (larger gear) has more teeth so the follower (smaller gear) turns around multiple times for each full turn of the driver
  • Gearing up gives you higher speed (because it takes only 1 turn of the driver to make the follower turn multiple times)
  • Gearing up is like 21st gear on a 21 speed bike - you go faster but more torque is necessary

Driver: 40 tooth

Follower: 8 tooth

When the driver turns around 1 time the follower turns around 5 times.

gear ratios
Gear Ratios
  • Each gear tooth on the driver turns one tooth on the follower
  • We want to be able to talk about the speed of gears in mathematical terms
  • Gear Ratios tell us how many times faster or slower the follower is rotating with respect to the driver
  • Gear Ratios are expressed in terms of the number of teeth on the follower over the number of teeth on the driver.
  • Gear Ratio =
gear ratios 2 of the same size gears
Gear Ratios: 2 of the same size gears

Driver: 40 tooth gear

Follower: 40 tooth gear

Which reduces to

which is sometimes expressed as 1:1

No Change in Speed

gear ratios gearing down
Gear Ratios: Gearing Down

Driver: 8 tooth

Follower: 40 tooth

Which reduces to

which can also be expressed as 5:1

The follower is 5 times slower than the driver

gear ratios gearing up
Gear Ratios: Gearing Up

Driver: 40 tooth

Follower: 8 tooth

Which reduces to

which can also be expressed as 1:5

The follower is 5 times faster than the driver

idle gears
Idle Gears
  • When a gear is placed directly between two others, that gear does not affect the gear ratio.
  • The gear ratio is computed using the driver and the last gear in the gear train.
  • The idle gear has no effect on a gear train except to change the direction of rotation

Which gear is the idler?

If a motor is attached to the axle with the green gear on it, which gear is the driver? Which is the follower?

other gears
Other Gears
  • Bevel Gears
    • Meshing at 90 degree angles
  • Rack and Pinion
    • Linear motion
double bevel gears
Double Bevel Gears
  • Work as Spur & Bevel Gears
  • Sizes: 12, 20, 36 tooth
crown gear
Crown Gear
  • Transfer motion in between planes (at angles)
  • Lego crown gear changes axis of rotation by 90 degrees
  • Crown gears can mesh with other crown gears and spur gears as well
  • Used in gumball machines, egg beaters
worm gear
Worm Gear
  • Inclined plane
  • 1 turn of the work gear moves by 1 tooth of any other gear
  • Spur Gear cannot turn worm gear
knob wheel
Knob Wheel
  • Not a true gear
  • Only works with another knob wheel
  • Can function like a gear – transfer rotary motion
compound gearing
Can change the speed of your follower by changing the gear configuration

Use two gears on an axle to get a larger gear ratio in your gear train

When a gear train similar to the one at right is used, the ratios of the meshing gears are multiplied to find the overall gear ratio

Compound Gearing
compound gear ratios
Compound Gear Ratios

The Lego gear train on the last slide had two sets of gears, each had a ratio of 40:8 (or 5:1). What is the ratio of the gear train?

Answer…

Try this one…

8 to 40, then 24 to 40, then 24 to 24

What is the overall gear ratio of this

Gear train?

If the 8 tooth gear is the driver and the

last 24 tooth gear the follower, is the gear

train geared up or down?

gear ratios22
Gear Ratios
  • Answer to the last question is 25:3
  • This means that for every 25 times you turn the driver, the follower will turn three times
  • If your driver is larger, your follower will turn more. If your driver is smaller your follower will turn fewer times
  • Remember the idle gears? They can be ignored when computing gear ratios