1. 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

2. 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

3. 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
Driver
Idle

4. 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

5. 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.

6. Lego Spur Gears Common sizes are 8, 16, 24, and 40 tooth
Correct Spacing
Horizontal
40 and holes between axles
40 and 8- 2 holes between axles
Vertical
40 and studs and 1 plate between studs holding axles
24 and stud between studs holding axles
Gears can be placed in a number of other combinations diagonally, but none other vertically or horizontally

7. 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

8. 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
Driver: 8 tooth
Follower: 40 tooth
The driver has to turn around 5 times to get the follower to turn once

9. 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.

10. 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 =

11. 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

12. 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

13. 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

14. 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?

15. Other Gears Bevel Gears Rack and Pinion Meshing at 90 degree angles
Linear motion

16. Double Bevel Gears
Work as Spur & Bevel Gears
Sizes: 12, 20, 36 tooth

17. 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

18. Worm Gear Inclined plane
1 turn of the work gear moves by 1 tooth of any other gear
Spur Gear cannot turn worm gear

19. Knob Wheel Not a true gear Only works with another knob wheel
Can function like a gear – transfer rotary motion

20. 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

21. 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?

22. 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